org.apache.commons.net.ftp

## Class FTPClient

- java.lang.Object
- - org.apache.commons.net.SocketClient
  - - org.apache.commons.net.ftp.FTP
    - - org.apache.commons.net.ftp.FTPClient

- All Implemented Interfaces:
    Configurable
  Direct Known Subclasses:
    FTPHTTPClient, FTPSClient

      public class FTPClient
      extends FTP
      implements Configurable

  FTPClient encapsulates all the functionality necessary to store and retrieve files from an FTP server. This class takes care of all low level details of interacting with an FTP server and provides a convenient higher level interface. As with all classes derived from `SocketClient`, you must first connect to the server with `connect` before doing anything, and finally `disconnect` after you're completely finished interacting with the server. Then you need to check the FTP reply code to see if the connection was successful. For example:

          FTPClient ftp = new FTPClient();
          FTPClientConfig config = new FTPClientConfig();
          config.setXXX(YYY); // change required options
          ftp.configure(config );
          boolean error = false;
          try {
            int reply;
            ftp.connect("ftp.foobar.com");
            System.out.println("Connected to " + server + ".");
            System.out.print(ftp.getReplyString());

            // After connection attempt, you should check the reply code to verify
            // success.
            reply = ftp.getReplyCode();

            if(!FTPReply.isPositiveCompletion(reply)) {
              ftp.disconnect();
              System.err.println("FTP server refused connection.");
              System.exit(1);
            }
            ... // transfer files
            ftp.logout();
          } catch(IOException e) {
            error = true;
            e.printStackTrace();
          } finally {
            if(ftp.isConnected()) {
              try {
                ftp.disconnect();
              } catch(IOException ioe) {
                // do nothing
              }
            }
            System.exit(error ? 1 : 0);
          }

  Immediately after connecting is the only real time you need to check the reply code (because connect is of type void). The convention for all the FTP command methods in FTPClient is such that they either return a boolean value or some other value. The boolean methods return true on a successful completion reply from the FTP server and false on a reply resulting in an error condition or failure. The methods returning a value other than boolean return a value containing the higher level data produced by the FTP command, or null if a reply resulted in an error condition or failure. If you want to access the exact FTP reply code causing a success or failure, you must call `getReplyCode` after a success or failure.

  The default settings for FTPClient are for it to use `FTP.ASCII_FILE_TYPE` , `FTP.NON_PRINT_TEXT_FORMAT` , `FTP.STREAM_TRANSFER_MODE` , and `FTP.FILE_STRUCTURE` . The only file types directly supported are `FTP.ASCII_FILE_TYPE` and `FTP.BINARY_FILE_TYPE` . Because there are at least 4 different EBCDIC encodings, we have opted not to provide direct support for EBCDIC. To transfer EBCDIC and other unsupported file types you must create your own filter InputStreams and OutputStreams and wrap them around the streams returned or required by the FTPClient methods. FTPClient uses the `NetASCII` filter streams to provide transparent handling of ASCII files. We will consider incorporating EBCDIC support if there is enough demand.

  `FTP.NON_PRINT_TEXT_FORMAT` , `FTP.STREAM_TRANSFER_MODE` , and `FTP.FILE_STRUCTURE` are the only supported formats, transfer modes, and file structures.

  Because the handling of sockets on different platforms can differ significantly, the FTPClient automatically issues a new PORT (or EPRT) command prior to every transfer requiring that the server connect to the client's data port. This ensures identical problem-free behavior on Windows, Unix, and Macintosh platforms. Additionally, it relieves programmers from having to issue the PORT (or EPRT) command themselves and dealing with platform dependent issues.

  Additionally, for security purposes, all data connections to the client are verified to ensure that they originated from the intended party (host and port). If a data connection is initiated by an unexpected party, the command will close the socket and throw an IOException. You may disable this behavior with `setRemoteVerificationEnabled()`.

  You should keep in mind that the FTP server may choose to prematurely close a connection if the client has been idle for longer than a given time period (usually 900 seconds). The FTPClient class will detect a premature FTP server connection closing when it receives a `FTPReply.SERVICE_NOT_AVAILABLE` response to a command. When that occurs, the FTP class method encountering that reply will throw an `FTPConnectionClosedException` . `FTPConnectionClosedException` is a subclass of `IOException` and therefore need not be caught separately, but if you are going to catch it separately, its catch block must appear before the more general `IOException` catch block. When you encounter an `FTPConnectionClosedException` , you must disconnect the connection with `disconnect()` to properly clean up the system resources used by FTPClient. Before disconnecting, you may check the last reply code and text with `getReplyCode` , `getReplyString` , and `getReplyStrings`. You may avoid server disconnections while the client is idle by periodically sending NOOP commands to the server.

  Rather than list it separately for each method, we mention here that every method communicating with the server and throwing an IOException can also throw a `MalformedServerReplyException` , which is a subclass of IOException. A MalformedServerReplyException will be thrown when the reply received from the server deviates enough from the protocol specification that it cannot be interpreted in a useful manner despite attempts to be as lenient as possible.

  Listing API Examples Both paged and unpaged examples of directory listings are available, as follows:

  Unpaged (whole list) access, using a parser accessible by auto-detect:

          FTPClient f = new FTPClient();
          f.connect(server);
          f.login(username, password);
          FTPFile[] files = f.listFiles(directory);

  Paged access, using a parser not accessible by auto-detect. The class defined in the first parameter of initateListParsing should be derived from org.apache.commons.net.FTPFileEntryParser:

          FTPClient f = new FTPClient();
          f.connect(server);
          f.login(username, password);
          FTPListParseEngine engine =
             f.initiateListParsing("com.whatever.YourOwnParser", directory);

          while (engine.hasNext()) {
             FTPFile[] files = engine.getNext(25);  // "page size" you want
             //do whatever you want with these files, display them, etc.
             //expensive FTPFile objects not created until needed.
          }

  Paged access, using a parser accessible by auto-detect:

          FTPClient f = new FTPClient();
          f.connect(server);
          f.login(username, password);
          FTPListParseEngine engine = f.initiateListParsing(directory);

          while (engine.hasNext()) {
             FTPFile[] files = engine.getNext(25);  // "page size" you want
             //do whatever you want with these files, display them, etc.
             //expensive FTPFile objects not created until needed.
          }

  For examples of using FTPClient on servers whose directory listings

  - use languages other than English
  - use date formats other than the American English "standard" `MM d yyyy`
  - are in different timezones and you need accurate timestamps for dependency checking as in Ant
  see `FTPClientConfig`.

  Control channel keep-alive feature:
  During file transfers, the data connection is busy, but the control connection is idle. FTP servers know that the control connection is in use, so won't close it through lack of activity, but it's a lot harder for network routers to know that the control and data connections are associated with each other. Some routers may treat the control connection as idle, and disconnect it if the transfer over the data connection takes longer than the allowable idle time for the router.
  One solution to this is to send a safe command (i.e. NOOP) over the control connection to reset the router's idle timer. This is enabled as follows:

           ftpClient.setControlKeepAliveTimeout(300); // set timeout to 5 minutes

  This will cause the file upload/download methods to send a NOOP approximately every 5 minutes.

  The implementation currently uses a `CopyStreamListener` which is passed to the `Util.copyStream(InputStream, OutputStream, int, long, CopyStreamListener, boolean)` method, so the timing is partially dependent on how long each block transfer takes.

  Note: this does not apply to the methods where the user is responsible for writing or reading the data stream, i.e. `retrieveFileStream(String)` , `storeFileStream(String)` and the other xxxFileStream methods

  See Also:
    `FTP_SYSTEM_TYPE`, `SYSTEM_TYPE_PROPERTIES`, `FTP`, `FTPConnectionClosedException`, `FTPFileEntryParser`, `FTPFileEntryParserFactory`, `DefaultFTPFileEntryParserFactory`, `FTPClientConfig`, `MalformedServerReplyException`

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `static int` | `ACTIVE_LOCAL_DATA_CONNECTION_MODE` A constant indicating the FTP session is expecting all transfers to occur between the client (local) and server and that the server should connect to the client's data port to initiate a data transfer.
    `static int` | `ACTIVE_REMOTE_DATA_CONNECTION_MODE` A constant indicating the FTP session is expecting all transfers to occur between two remote servers and that the server the client is connected to should connect to the other server's data port to initiate a data transfer.
    `static String` | `FTP_SYSTEM_TYPE` The system property ("org.apache.commons.net.ftp.systemType") which can be used to override the system type. If defined, the value will be used to create any automatically created parsers.
    `static String` | `FTP_SYSTEM_TYPE_DEFAULT` The system property ("org.apache.commons.net.ftp.systemType.default") which can be used as the default system type. If defined, the value will be used if the SYST command fails.
    `static int` | `PASSIVE_LOCAL_DATA_CONNECTION_MODE` A constant indicating the FTP session is expecting all transfers to occur between the client (local) and server and that the server is in passive mode, requiring the client to connect to the server's data port to initiate a transfer.
    `static int` | `PASSIVE_REMOTE_DATA_CONNECTION_MODE` A constant indicating the FTP session is expecting all transfers to occur between two remote servers and that the server the client is connected to is in passive mode, requiring the other server to connect to the first server's data port to initiate a data transfer.
    `static String` | `SYSTEM_TYPE_PROPERTIES` The name of an optional systemType properties file ("/systemType.properties"), which is loaded using `Class.getResourceAsStream(String)`. The entries are the systemType (as determined by `getSystemType()`) and the values are the replacement type or parserClass, which is passed to `FTPFileEntryParserFactory.createFileEntryParser(String)`. For example:

    - ### Fields inherited from class org.apache.commons.net.ftp.FTP

      `_commandSupport_, _controlEncoding, _controlInput_, _controlOutput_, _newReplyString, _replyCode, _replyLines, _replyString, ASCII_FILE_TYPE, BINARY_FILE_TYPE, BLOCK_TRANSFER_MODE, CARRIAGE_CONTROL_TEXT_FORMAT, COMPRESSED_TRANSFER_MODE, DEFAULT_CONTROL_ENCODING, DEFAULT_DATA_PORT, DEFAULT_PORT, EBCDIC_FILE_TYPE, FILE_STRUCTURE, LOCAL_FILE_TYPE, NON_PRINT_TEXT_FORMAT, PAGE_STRUCTURE, RECORD_STRUCTURE, REPLY_CODE_LEN, STREAM_TRANSFER_MODE, strictMultilineParsing, TELNET_TEXT_FORMAT`

    - ### Fields inherited from class org.apache.commons.net.SocketClient

      `_defaultPort_, _input_, _output_, _serverSocketFactory_, _socket_, _socketFactory_, _timeout_, connectTimeout, NETASCII_EOL`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `FTPClient()` Default FTPClient constructor.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected void` | `_connectAction_()` Initiates control connections and gets initial reply.
    `protected Socket` | `_openDataConnection_(FTPCmd command, String arg)` Establishes a data connection with the FTP server, returning a Socket for the connection if successful.
    `protected Socket` | `_openDataConnection_(int command, String arg)` Deprecated. (3.3) Use `_openDataConnection_(FTPCmd, String)` instead
    `protected Socket` | `_openDataConnection_(String command, String arg)` Establishes a data connection with the FTP server, returning a Socket for the connection if successful.
    `protected void` | `_parseExtendedPassiveModeReply(String reply)`
    `protected void` | `_parsePassiveModeReply(String reply)`
    `protected boolean` | `_retrieveFile(String command, String remote, OutputStream local)`
    `protected InputStream` | `_retrieveFileStream(String command, String remote)`
    `protected boolean` | `_storeFile(String command, String remote, InputStream local)`
    `protected OutputStream` | `_storeFileStream(String command, String remote)`
    `boolean` | `abort()` Abort a transfer in progress.
    `boolean` | `allocate(int bytes)` Reserve a number of bytes on the server for the next file transfer.
    `boolean` | `allocate(int bytes, int recordSize)` Reserve space on the server for the next file transfer.
    `boolean` | `appendFile(String remote, InputStream local)` Appends to a file on the server with the given name, taking input from the given InputStream.
    `OutputStream` | `appendFileStream(String remote)` Returns an OutputStream through which data can be written to append to a file on the server with the given name.
    `boolean` | `changeToParentDirectory()` Change to the parent directory of the current working directory.
    `boolean` | `changeWorkingDirectory(String pathname)` Change the current working directory of the FTP session.
    `boolean` | `completePendingCommand()` There are a few FTPClient methods that do not complete the entire sequence of FTP commands to complete a transaction.
    `void` | `configure(FTPClientConfig config)` Implementation of the `Configurable` interface.
    `boolean` | `deleteFile(String pathname)` Deletes a file on the FTP server.
    `void` | `disconnect()` Closes the connection to the FTP server and restores connection parameters to the default values.
    `boolean` | `doCommand(String command, String params)` Issue a command and wait for the reply.
    `String[]` | `doCommandAsStrings(String command, String params)` Issue a command and wait for the reply, returning it as an array of strings.
    `void` | `enterLocalActiveMode()` Set the current data connection mode to `ACTIVE_LOCAL_DATA_CONNECTION_MODE`.
    `void` | `enterLocalPassiveMode()` Set the current data connection mode to `PASSIVE_LOCAL_DATA_CONNECTION_MODE` .
    `boolean` | `enterRemoteActiveMode(InetAddress host, int port)` Set the current data connection mode to `ACTIVE_REMOTE_DATA_CONNECTION` .
    `boolean` | `enterRemotePassiveMode()` Set the current data connection mode to `PASSIVE_REMOTE_DATA_CONNECTION_MODE` .
    `boolean` | `features()` Query the server for supported features.
    `String` | `featureValue(String feature)` Query the server for a supported feature, and returns the its value (if any).
    `String[]` | `featureValues(String feature)` Query the server for a supported feature, and returns its values (if any).
    `boolean` | `getAutodetectUTF8()` Tells if automatic server encoding detection is enabled or disabled.
    `int` | `getBufferSize()` Retrieve the current internal buffer size for buffered data streams.
    `int` | `getControlKeepAliveReplyTimeout()` Get how long to wait for control keep-alive message replies.
    `long` | `getControlKeepAliveTimeout()` Get the time to wait between sending control connection keepalive messages.
    `CopyStreamListener` | `getCopyStreamListener()` Obtain the currently active listener.
    `int` | `getDataConnectionMode()` Returns the current data connection mode (one of the `_DATA_CONNECTION_MODE` constants.
    `protected String` | `getListArguments(String pathname)`
    `boolean` | `getListHiddenFiles()`
    `String` | `getModificationTime(String pathname)` Issue the FTP MDTM command (not supported by all servers to retrieve the last modification time of a file.
    `String` | `getPassiveHost()` Returns the hostname or IP address (in the form of a string) returned by the server when entering passive mode.
    `InetAddress` | `getPassiveLocalIPAddress()` Set the local IP address in passive mode.
    `int` | `getPassivePort()` If in passive mode, returns the data port of the passive host.
    `int` | `getReceiveDataSocketBufferSize()` Retrieve the value to be used for the data socket SO_RCVBUF option.
    `long` | `getRestartOffset()` Fetches the restart offset.
    `int` | `getSendDataSocketBufferSize()` Retrieve the value to be used for the data socket SO_SNDBUF option.
    `String` | `getStatus()` Issue the FTP STAT command to the server.
    `String` | `getStatus(String pathname)` Issue the FTP STAT command to the server for a given pathname.
    `String` | `getSystemName()` Deprecated. use `getSystemType()` instead
    `String` | `getSystemType()` Fetches the system type from the server and returns the string.
    `boolean` | `hasFeature(String feature)` Query the server for a supported feature.
    `boolean` | `hasFeature(String feature, String value)` Query the server for a supported feature with particular value, for example "AUTH SSL" or "AUTH TLS".
    `FTPListParseEngine` | `initiateListParsing()` Using the default autodetect mechanism, initialize an FTPListParseEngine object containing a raw file information for the current working directory on the server This information is obtained through the LIST command.
    `FTPListParseEngine` | `initiateListParsing(String pathname)` Using the default autodetect mechanism, initialize an FTPListParseEngine object containing a raw file information for the supplied directory.
    `FTPListParseEngine` | `initiateListParsing(String parserKey, String pathname)` Using the supplied parser key, initialize an FTPListParseEngine object containing a raw file information for the supplied directory.
    `boolean` | `isRemoteVerificationEnabled()` Return whether or not verification of the remote host participating in data connections is enabled.
    `boolean` | `isUseEPSVwithIPv4()` Whether should attempt to use EPSV with IPv4.
    `FTPFile[]` | `listDirectories()` Using the default system autodetect mechanism, obtain a list of directories contained in the current working directory.
    `FTPFile[]` | `listDirectories(String parent)` Using the default system autodetect mechanism, obtain a list of directories contained in the specified directory.
    `FTPFile[]` | `listFiles()` Using the default system autodetect mechanism, obtain a list of file information for the current working directory.
    `FTPFile[]` | `listFiles(String pathname)` Using the default system autodetect mechanism, obtain a list of file information for the current working directory or for just a single file.
    `FTPFile[]` | `listFiles(String pathname, FTPFileFilter filter)` Version of `listFiles(String)` which allows a filter to be provided.
    `String` | `listHelp()` Fetches the system help information from the server and returns the full string.
    `String` | `listHelp(String command)` Fetches the help information for a given command from the server and returns the full string.
    `String[]` | `listNames()` Obtain a list of filenames in the current working directory This information is obtained through the NLST command.
    `String[]` | `listNames(String pathname)` Obtain a list of filenames in a directory (or just the name of a given file, which is not particularly useful).
    `boolean` | `login(String username, String password)` Login to the FTP server using the provided username and password.
    `boolean` | `login(String username, String password, String account)` Login to the FTP server using the provided username, password, and account.
    `boolean` | `logout()` Logout of the FTP server by sending the QUIT command.
    `boolean` | `makeDirectory(String pathname)` Creates a new subdirectory on the FTP server in the current directory (if a relative pathname is given) or where specified (if an absolute pathname is given).
    `FTPFile[]` | `mlistDir()` Generate a directory listing for the current directory using the MLSD command.
    `FTPFile[]` | `mlistDir(String pathname)` Generate a directory listing using the MLSD command.
    `FTPFile[]` | `mlistDir(String pathname, FTPFileFilter filter)` Generate a directory listing using the MLSD command.
    `FTPFile` | `mlistFile(String pathname)` Get file details using the MLST command
    `String` | `printWorkingDirectory()` Returns the pathname of the current working directory.
    `boolean` | `remoteAppend(String filename)` Initiate a server to server file transfer.
    `boolean` | `remoteRetrieve(String filename)` Initiate a server to server file transfer.
    `boolean` | `remoteStore(String filename)` Initiate a server to server file transfer.
    `boolean` | `remoteStoreUnique()` Initiate a server to server file transfer.
    `boolean` | `remoteStoreUnique(String filename)` Initiate a server to server file transfer.
    `boolean` | `removeDirectory(String pathname)` Removes a directory on the FTP server (if empty).
    `boolean` | `rename(String from, String to)` Renames a remote file.
    `protected boolean` | `restart(long offset)` Restart a `STREAM_TRANSFER_MODE` file transfer starting from the given offset.
    `boolean` | `retrieveFile(String remote, OutputStream local)` Retrieves a named file from the server and writes it to the given OutputStream.
    `InputStream` | `retrieveFileStream(String remote)` Returns an InputStream from which a named file from the server can be read.
    `boolean` | `sendNoOp()` Sends a NOOP command to the FTP server.
    `boolean` | `sendSiteCommand(String arguments)` Send a site specific command.
    `void` | `setActiveExternalIPAddress(String ipAddress)` Set the external IP address in active mode.
    `void` | `setActivePortRange(int minPort, int maxPort)` Set the client side port range in active mode.
    `void` | `setAutodetectUTF8(boolean autodetect)` Enables or disables automatic server encoding detection (only UTF-8 supported).
    `void` | `setBufferSize(int bufSize)` Set the internal buffer size for buffered data streams.
    `void` | `setControlKeepAliveReplyTimeout(int timeout)` Set how long to wait for control keep-alive message replies.
    `void` | `setControlKeepAliveTimeout(long controlIdle)` Set the time to wait between sending control connection keepalive messages when processing file upload or download.
    `void` | `setCopyStreamListener(CopyStreamListener listener)` Set the listener to be used when performing store/retrieve operations.
    `void` | `setDataTimeout(int timeout)` Sets the timeout in milliseconds to use when reading from the data connection.
    `boolean` | `setFileStructure(int structure)` Sets the file structure.
    `boolean` | `setFileTransferMode(int mode)` Sets the transfer mode.
    `boolean` | `setFileType(int fileType)` Sets the file type to be transferred.
    `boolean` | `setFileType(int fileType, int formatOrByteSize)` Sets the file type to be transferred and the format.
    `void` | `setListHiddenFiles(boolean listHiddenFiles)` You can set this to true if you would like to get hidden files when `listFiles(java.lang.String)` too.
    `boolean` | `setModificationTime(String pathname, String timeval)` Issue the FTP MFMT command (not supported by all servers) which sets the last modified time of a file.
    `void` | `setParserFactory(FTPFileEntryParserFactory parserFactory)` set the factory used for parser creation to the supplied factory object.
    `void` | `setPassiveLocalIPAddress(InetAddress inetAddress)` Set the local IP address to use in passive mode.
    `void` | `setPassiveLocalIPAddress(String ipAddress)` Set the local IP address to use in passive mode.
    `void` | `setPassiveNatWorkaround(boolean enabled)` Enable or disable passive mode NAT workaround.
    `void` | `setReceieveDataSocketBufferSize(int bufSize)` Sets the value to be used for the data socket SO_RCVBUF option.
    `void` | `setRemoteVerificationEnabled(boolean enable)` Enable or disable verification that the remote host taking part of a data connection is the same as the host to which the control connection is attached.
    `void` | `setReportActiveExternalIPAddress(String ipAddress)` Set the external IP address to report in EPRT/PORT commands in active mode.
    `void` | `setRestartOffset(long offset)` Sets the restart offset for file transfers.
    `void` | `setSendDataSocketBufferSize(int bufSize)` Sets the value to be used for the data socket SO_SNDBUF option.
    `void` | `setUseEPSVwithIPv4(boolean selected)` Set whether to use EPSV with IPv4.
    `boolean` | `storeFile(String remote, InputStream local)` Stores a file on the server using the given name and taking input from the given InputStream.
    `OutputStream` | `storeFileStream(String remote)` Returns an OutputStream through which data can be written to store a file on the server using the given name.
    `boolean` | `storeUniqueFile(InputStream local)` Stores a file on the server using a unique name assigned by the server and taking input from the given InputStream.
    `boolean` | `storeUniqueFile(String remote, InputStream local)` Stores a file on the server using a unique name derived from the given name and taking input from the given InputStream.
    `OutputStream` | `storeUniqueFileStream()` Returns an OutputStream through which data can be written to store a file on the server using a unique name assigned by the server.
    `OutputStream` | `storeUniqueFileStream(String remote)` Returns an OutputStream through which data can be written to store a file on the server using a unique name derived from the given name.
    `boolean` | `structureMount(String pathname)` Issue the FTP SMNT command.

    - ### Methods inherited from class org.apache.commons.net.ftp.FTP

      `__getReplyNoReport, __noop, abor, acct, allo, allo, appe, cdup, cwd, dele, eprt, epsv, feat, getCommandSupport, getControlEncoding, getReply, getReplyCode, getReplyString, getReplyStrings, help, help, isStrictMultilineParsing, list, list, mdtm, mfmt, mkd, mlsd, mlsd, mlst, mlst, mode, nlst, nlst, noop, pass, pasv, port, pwd, quit, rein, rest, retr, rmd, rnfr, rnto, sendCommand, sendCommand, sendCommand, sendCommand, sendCommand, sendCommand, setControlEncoding, setStrictMultilineParsing, site, smnt, stat, stat, stor, stou, stou, stru, syst, type, type, user`

    - ### Methods inherited from class org.apache.commons.net.SocketClient

      `addProtocolCommandListener, connect, connect, connect, connect, connect, connect, createCommandSupport, fireCommandSent, fireReplyReceived, getCharset, getCharsetName, getConnectTimeout, getDefaultPort, getDefaultTimeout, getKeepAlive, getLocalAddress, getLocalPort, getProxy, getReceiveBufferSize, getRemoteAddress, getRemotePort, getSendBufferSize, getServerSocketFactory, getSoLinger, getSoTimeout, getTcpNoDelay, isAvailable, isConnected, removeProtocolCommandListener, setCharset, setConnectTimeout, setDefaultPort, setDefaultTimeout, setKeepAlive, setProxy, setReceiveBufferSize, setSendBufferSize, setServerSocketFactory, setSocketFactory, setSoLinger, setSoTimeout, setTcpNoDelay, verifyRemote`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### FTP_SYSTEM_TYPE

          public static final String FTP_SYSTEM_TYPE

      The system property ("org.apache.commons.net.ftp.systemType") which can be used to override the system type.
      If defined, the value will be used to create any automatically created parsers.
      Since:
        3.0
      See Also:
        Constant Field Values

    - #### FTP_SYSTEM_TYPE_DEFAULT

          public static final String FTP_SYSTEM_TYPE_DEFAULT

      The system property ("org.apache.commons.net.ftp.systemType.default") which can be used as the default system type.
      If defined, the value will be used if the SYST command fails.
      Since:
        3.1
      See Also:
        Constant Field Values

    - #### SYSTEM_TYPE_PROPERTIES

          public static final String SYSTEM_TYPE_PROPERTIES

      The name of an optional systemType properties file ("/systemType.properties"), which is loaded using `Class.getResourceAsStream(String)`.
      The entries are the systemType (as determined by `getSystemType()`) and the values are the replacement type or parserClass, which is passed to `FTPFileEntryParserFactory.createFileEntryParser(String)`.
      For example:

           Plan 9=Unix
           OS410=org.apache.commons.net.ftp.parser.OS400FTPEntryParser

      Since:
        3.0
      See Also:
        Constant Field Values

    - #### ACTIVE_LOCAL_DATA_CONNECTION_MODE

          public static final int ACTIVE_LOCAL_DATA_CONNECTION_MODE

      A constant indicating the FTP session is expecting all transfers to occur between the client (local) and server and that the server should connect to the client's data port to initiate a data transfer. This is the default data connection mode when and FTPClient instance is created.
      See Also:
        Constant Field Values

    - #### ACTIVE_REMOTE_DATA_CONNECTION_MODE

          public static final int ACTIVE_REMOTE_DATA_CONNECTION_MODE

      A constant indicating the FTP session is expecting all transfers to occur between two remote servers and that the server the client is connected to should connect to the other server's data port to initiate a data transfer.
      See Also:
        Constant Field Values

    - #### PASSIVE_LOCAL_DATA_CONNECTION_MODE

          public static final int PASSIVE_LOCAL_DATA_CONNECTION_MODE

      A constant indicating the FTP session is expecting all transfers to occur between the client (local) and server and that the server is in passive mode, requiring the client to connect to the server's data port to initiate a transfer.
      See Also:
        Constant Field Values

    - #### PASSIVE_REMOTE_DATA_CONNECTION_MODE

          public static final int PASSIVE_REMOTE_DATA_CONNECTION_MODE

      A constant indicating the FTP session is expecting all transfers to occur between two remote servers and that the server the client is connected to is in passive mode, requiring the other server to connect to the first server's data port to initiate a data transfer.
      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### FTPClient

          public FTPClient()

      Default FTPClient constructor. Creates a new FTPClient instance with the data connection mode set to `ACTIVE_LOCAL_DATA_CONNECTION_MODE` , the file type set to `FTP.ASCII_FILE_TYPE` , the file format set to `FTP.NON_PRINT_TEXT_FORMAT` , the file structure set to `FTP.FILE_STRUCTURE` , and the transfer mode set to `FTP.STREAM_TRANSFER_MODE` .

      The list parsing auto-detect feature can be configured to use lenient future dates (short dates may be up to one day in the future) as follows:

           FTPClient ftp = new FTPClient();
           FTPClientConfig config = new FTPClientConfig();
           config.setLenientFutureDates(true);
           ftp.configure(config );

  - ### Method Detail

    - #### _parsePassiveModeReply

          protected void _parsePassiveModeReply(String reply)
                                         throws MalformedServerReplyException

      Throws:
        `MalformedServerReplyException`
      Since:
        3.1

    - #### _parseExtendedPassiveModeReply

          protected void _parseExtendedPassiveModeReply(String reply)
                                                 throws MalformedServerReplyException

      Throws:
        `MalformedServerReplyException`

    - #### _storeFile

          protected boolean _storeFile(String command,
                           String remote,
                           InputStream local)
                                throws IOException

      Throws:
        `IOException`
      Since:
        3.1

    - #### _storeFileStream

          protected OutputStream _storeFileStream(String command,
                                      String remote)
                                           throws IOException

      Throws:
        `IOException`
      Since:
        3.1

    - #### _openDataConnection_

          @Deprecated
          protected Socket _openDataConnection_(int command,
                                               String arg)
                                         throws IOException

      Deprecated. (3.3) Use `_openDataConnection_(FTPCmd, String)` instead
      Establishes a data connection with the FTP server, returning a Socket for the connection if successful. If a restart offset has been set with `setRestartOffset(long)`, a REST command is issued to the server with the offset as an argument before establishing the data connection. Active mode connections also cause a local PORT command to be issued.

      Parameters:
        `command` - The int representation of the FTP command to send.
        `arg` - The arguments to the FTP command. If this parameter is set to null, then the command is sent with no argument.
      Returns:
        A Socket corresponding to the established data connection. Null is returned if an FTP protocol error is reported at any point during the establishment and initialization of the connection.
      Throws:
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### _openDataConnection_

          protected Socket _openDataConnection_(FTPCmd command,
                                    String arg)
                                         throws IOException

      Establishes a data connection with the FTP server, returning a Socket for the connection if successful. If a restart offset has been set with `setRestartOffset(long)`, a REST command is issued to the server with the offset as an argument before establishing the data connection. Active mode connections also cause a local PORT command to be issued.

      Parameters:
        `command` - The int representation of the FTP command to send.
        `arg` - The arguments to the FTP command. If this parameter is set to null, then the command is sent with no argument.
      Returns:
        A Socket corresponding to the established data connection. Null is returned if an FTP protocol error is reported at any point during the establishment and initialization of the connection.
      Throws:
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
      Since:
        3.3

    - #### _openDataConnection_

          protected Socket _openDataConnection_(String command,
                                    String arg)
                                         throws IOException

      Establishes a data connection with the FTP server, returning a Socket for the connection if successful. If a restart offset has been set with `setRestartOffset(long)`, a REST command is issued to the server with the offset as an argument before establishing the data connection. Active mode connections also cause a local PORT command to be issued.

      Parameters:
        `command` - The text representation of the FTP command to send.
        `arg` - The arguments to the FTP command. If this parameter is set to null, then the command is sent with no argument.
      Returns:
        A Socket corresponding to the established data connection. Null is returned if an FTP protocol error is reported at any point during the establishment and initialization of the connection.
      Throws:
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
      Since:
        3.1

    - #### _connectAction_

          protected void _connectAction_()
                                  throws IOException

      Description copied from class: `FTP`
      Initiates control connections and gets initial reply. Initializes `FTP._controlInput_` and `FTP._controlOutput_`.
      Overrides:
        `_connectAction_` in class `FTP`
      Throws:
        `IOException`

    - #### setDataTimeout

          public void setDataTimeout(int timeout)

      Sets the timeout in milliseconds to use when reading from the data connection. This timeout will be set immediately after opening the data connection, provided that the value is ≥ 0.

      Note: the timeout will also be applied when calling accept() whilst establishing an active local data connection.

      Parameters:
        `timeout` - The default timeout in milliseconds that is used when opening a data connection socket. The value 0 means an infinite timeout.

    - #### setParserFactory

          public void setParserFactory(FTPFileEntryParserFactory parserFactory)

      set the factory used for parser creation to the supplied factory object.
      Parameters:
        `parserFactory` - factory object used to create FTPFileEntryParsers
      See Also:
        `FTPFileEntryParserFactory`, `DefaultFTPFileEntryParserFactory`

    - #### disconnect

          public void disconnect()
                          throws IOException

      Closes the connection to the FTP server and restores connection parameters to the default values.

      Overrides:
        `disconnect` in class `FTP`
      Throws:
        `IOException` - If an error occurs while disconnecting.

    - #### setRemoteVerificationEnabled

          public void setRemoteVerificationEnabled(boolean enable)

      Enable or disable verification that the remote host taking part of a data connection is the same as the host to which the control connection is attached. The default is for verification to be enabled. You may set this value at any time, whether the FTPClient is currently connected or not.

      Parameters:
        `enable` - True to enable verification, false to disable verification.

    - #### isRemoteVerificationEnabled

          public boolean isRemoteVerificationEnabled()

      Return whether or not verification of the remote host participating in data connections is enabled. The default behavior is for verification to be enabled.

      Returns:
        True if verification is enabled, false if not.

    - #### login

          public boolean login(String username,
                      String password)
                        throws IOException

      Login to the FTP server using the provided username and password.

      Parameters:
        `username` - The username to login under.
        `password` - The password to use.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### login

          public boolean login(String username,
                      String password,
                      String account)
                        throws IOException

      Login to the FTP server using the provided username, password, and account. If no account is required by the server, only the username and password, the account information is not used.

      Parameters:
        `username` - The username to login under.
        `password` - The password to use.
        `account` - The account to use.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### logout

          public boolean logout()
                         throws IOException

      Logout of the FTP server by sending the QUIT command.

      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### changeWorkingDirectory

          public boolean changeWorkingDirectory(String pathname)
                                         throws IOException

      Change the current working directory of the FTP session.

      Parameters:
        `pathname` - The new current working directory.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### changeToParentDirectory

          public boolean changeToParentDirectory()
                                          throws IOException

      Change to the parent directory of the current working directory.

      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### structureMount

          public boolean structureMount(String pathname)
                                 throws IOException

      Issue the FTP SMNT command.

      Parameters:
        `pathname` - The pathname to mount.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### enterLocalActiveMode

          public void enterLocalActiveMode()

      Set the current data connection mode to `ACTIVE_LOCAL_DATA_CONNECTION_MODE`. No communication with the FTP server is conducted, but this causes all future data transfers to require the FTP server to connect to the client's data port. Additionally, to accommodate differences between socket implementations on different platforms, this method causes the client to issue a PORT command before every data transfer.

    - #### enterLocalPassiveMode

          public void enterLocalPassiveMode()

      Set the current data connection mode to `PASSIVE_LOCAL_DATA_CONNECTION_MODE` . Use this method only for data transfers between the client and server. This method causes a PASV (or EPSV) command to be issued to the server before the opening of every data connection, telling the server to open a data port to which the client will connect to conduct data transfers. The FTPClient will stay in `PASSIVE_LOCAL_DATA_CONNECTION_MODE` until the mode is changed by calling some other method such as `enterLocalActiveMode()`

      N.B. currently calling any connect method will reset the mode to ACTIVE_LOCAL_DATA_CONNECTION_MODE.

    - #### enterRemoteActiveMode

          public boolean enterRemoteActiveMode(InetAddress host,
                                      int port)
                                        throws IOException

      Set the current data connection mode to `ACTIVE_REMOTE_DATA_CONNECTION` . Use this method only for server to server data transfers. This method issues a PORT command to the server, indicating the other server and port to which it should connect for data transfers. You must call this method before EVERY server to server transfer attempt. The FTPClient will NOT automatically continue to issue PORT commands. You also must remember to call `enterLocalActiveMode()` if you wish to return to the normal data connection mode.

      Parameters:
        `host` - The passive mode server accepting connections for data transfers.
        `port` - The passive mode server's data port.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### enterRemotePassiveMode

          public boolean enterRemotePassiveMode()
                                         throws IOException

      Set the current data connection mode to `PASSIVE_REMOTE_DATA_CONNECTION_MODE` . Use this method only for server to server data transfers. This method issues a PASV command to the server, telling it to open a data port to which the active server will connect to conduct data transfers. You must call this method before EVERY server to server transfer attempt. The FTPClient will NOT automatically continue to issue PASV commands. You also must remember to call `enterLocalActiveMode()` if you wish to return to the normal data connection mode.

      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### getPassiveHost

          public String getPassiveHost()

      Returns the hostname or IP address (in the form of a string) returned by the server when entering passive mode. If not in passive mode, returns null. This method only returns a valid value AFTER a data connection has been opened after a call to `enterLocalPassiveMode()`. This is because FTPClient sends a PASV command to the server only just before opening a data connection, and not when you call `enterLocalPassiveMode()`.

      Returns:
        The passive host name if in passive mode, otherwise null.

    - #### getPassivePort

          public int getPassivePort()

      If in passive mode, returns the data port of the passive host. This method only returns a valid value AFTER a data connection has been opened after a call to `enterLocalPassiveMode()`. This is because FTPClient sends a PASV command to the server only just before opening a data connection, and not when you call `enterLocalPassiveMode()`.

      Returns:
        The data port of the passive server. If not in passive mode, undefined.

    - #### getDataConnectionMode

          public int getDataConnectionMode()

      Returns the current data connection mode (one of the `_DATA_CONNECTION_MODE` constants.

      Returns:
        The current data connection mode (one of the `_DATA_CONNECTION_MODE` constants.

    - #### setActivePortRange

          public void setActivePortRange(int minPort,
                                int maxPort)

      Set the client side port range in active mode.

      Parameters:
        `minPort` - The lowest available port (inclusive).
        `maxPort` - The highest available port (inclusive).
      Since:
        2.2

    - #### setActiveExternalIPAddress

          public void setActiveExternalIPAddress(String ipAddress)
                                          throws UnknownHostException

      Set the external IP address in active mode. Useful when there are multiple network cards.

      Parameters:
        `ipAddress` - The external IP address of this machine.
      Throws:
        `UnknownHostException` - if the ipAddress cannot be resolved
      Since:
        2.2

    - #### setPassiveLocalIPAddress

          public void setPassiveLocalIPAddress(String ipAddress)
                                        throws UnknownHostException

      Set the local IP address to use in passive mode. Useful when there are multiple network cards.

      Parameters:
        `ipAddress` - The local IP address of this machine.
      Throws:
        `UnknownHostException` - if the ipAddress cannot be resolved

    - #### setPassiveLocalIPAddress

          public void setPassiveLocalIPAddress(InetAddress inetAddress)

      Set the local IP address to use in passive mode. Useful when there are multiple network cards.

      Parameters:
        `inetAddress` - The local IP address of this machine.

    - #### getPassiveLocalIPAddress

          public InetAddress getPassiveLocalIPAddress()

      Set the local IP address in passive mode. Useful when there are multiple network cards.

      Returns:
        The local IP address in passive mode.

    - #### setReportActiveExternalIPAddress

          public void setReportActiveExternalIPAddress(String ipAddress)
                                                throws UnknownHostException

      Set the external IP address to report in EPRT/PORT commands in active mode. Useful when there are multiple network cards.

      Parameters:
        `ipAddress` - The external IP address of this machine.
      Throws:
        `UnknownHostException` - if the ipAddress cannot be resolved
      Since:
        3.1
      See Also:
        `getReportHostAddress()`

    - #### setFileType

          public boolean setFileType(int fileType)
                              throws IOException

      Sets the file type to be transferred. This should be one of `FTP.ASCII_FILE_TYPE` , `FTP.BINARY_FILE_TYPE`, etc. The file type only needs to be set when you want to change the type. After changing it, the new type stays in effect until you change it again. The default file type is `FTP.ASCII_FILE_TYPE` if this method is never called.
      The server default is supposed to be ASCII (see RFC 959), however many ftp servers default to BINARY. To ensure correct operation with all servers, always specify the appropriate file type after connecting to the server.

      N.B. currently calling any connect method will reset the type to FTP.ASCII_FILE_TYPE.

      Parameters:
        `fileType` - The `_FILE_TYPE` constant indcating the type of file.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### setFileType

          public boolean setFileType(int fileType,
                            int formatOrByteSize)
                              throws IOException

      Sets the file type to be transferred and the format. The type should be one of `FTP.ASCII_FILE_TYPE` , `FTP.BINARY_FILE_TYPE` , etc. The file type only needs to be set when you want to change the type. After changing it, the new type stays in effect until you change it again. The default file type is `FTP.ASCII_FILE_TYPE` if this method is never called.
      The server default is supposed to be ASCII (see RFC 959), however many ftp servers default to BINARY. To ensure correct operation with all servers, always specify the appropriate file type after connecting to the server.
      The format should be one of the FTP class `TEXT_FORMAT` constants, or if the type is `FTP.LOCAL_FILE_TYPE` , the format should be the byte size for that type. The default format is `FTP.NON_PRINT_TEXT_FORMAT` if this method is never called.

      N.B. currently calling any connect method will reset the type to FTP.ASCII_FILE_TYPE and the formatOrByteSize to FTP.NON_PRINT_TEXT_FORMAT.

      Parameters:
        `fileType` - The `_FILE_TYPE` constant indcating the type of file.
        `formatOrByteSize` - The format of the file (one of the `_FORMAT` constants. In the case of `LOCAL_FILE_TYPE`, the byte size.

      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### setFileStructure

          public boolean setFileStructure(int structure)
                                   throws IOException

      Sets the file structure. The default structure is `FTP.FILE_STRUCTURE` if this method is never called or if a connect method is called.

      Parameters:
        `structure` - The structure of the file (one of the FTP class `_STRUCTURE` constants).
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### setFileTransferMode

          public boolean setFileTransferMode(int mode)
                                      throws IOException

      Sets the transfer mode. The default transfer mode `FTP.STREAM_TRANSFER_MODE` if this method is never called or if a connect method is called.

      Parameters:
        `mode` - The new transfer mode to use (one of the FTP class `_TRANSFER_MODE` constants).
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### remoteRetrieve

          public boolean remoteRetrieve(String filename)
                                 throws IOException

      Initiate a server to server file transfer. This method tells the server to which the client is connected to retrieve a given file from the other server.

      Parameters:
        `filename` - The name of the file to retrieve.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### remoteStore

          public boolean remoteStore(String filename)
                              throws IOException

      Initiate a server to server file transfer. This method tells the server to which the client is connected to store a file on the other server using the given filename. The other server must have had a `remoteRetrieve` issued to it by another FTPClient.

      Parameters:
        `filename` - The name to call the file that is to be stored.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### remoteStoreUnique

          public boolean remoteStoreUnique(String filename)
                                    throws IOException

      Initiate a server to server file transfer. This method tells the server to which the client is connected to store a file on the other server using a unique filename based on the given filename. The other server must have had a `remoteRetrieve` issued to it by another FTPClient.

      Parameters:
        `filename` - The name on which to base the filename of the file that is to be stored.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### remoteStoreUnique

          public boolean remoteStoreUnique()
                                    throws IOException

      Initiate a server to server file transfer. This method tells the server to which the client is connected to store a file on the other server using a unique filename. The other server must have had a `remoteRetrieve` issued to it by another FTPClient. Many FTP servers require that a base filename be given from which the unique filename can be derived. For those servers use the other version of `remoteStoreUnique`

      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### remoteAppend

          public boolean remoteAppend(String filename)
                               throws IOException

      Initiate a server to server file transfer. This method tells the server to which the client is connected to append to a given file on the other server. The other server must have had a `remoteRetrieve` issued to it by another FTPClient.

      Parameters:
        `filename` - The name of the file to be appended to, or if the file does not exist, the name to call the file being stored.

      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### completePendingCommand

          public boolean completePendingCommand()
                                         throws IOException

      There are a few FTPClient methods that do not complete the entire sequence of FTP commands to complete a transaction. These commands require some action by the programmer after the reception of a positive intermediate command. After the programmer's code completes its actions, it must call this method to receive the completion reply from the server and verify the success of the entire transaction.

      For example,

           InputStream input;
           OutputStream output;
           input  = new FileInputStream("foobaz.txt");
           output = ftp.storeFileStream("foobar.txt")
           if(!FTPReply.isPositiveIntermediate(ftp.getReplyCode())) {
               input.close();
               output.close();
               ftp.logout();
               ftp.disconnect();
               System.err.println("File transfer failed.");
               System.exit(1);
           }
           Util.copyStream(input, output);
           input.close();
           output.close();
           // Must call completePendingCommand() to finish command.
           if(!ftp.completePendingCommand()) {
               ftp.logout();
               ftp.disconnect();
               System.err.println("File transfer failed.");
               System.exit(1);
           }

      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### retrieveFile

          public boolean retrieveFile(String remote,
                             OutputStream local)
                               throws IOException

      Retrieves a named file from the server and writes it to the given OutputStream. This method does NOT close the given OutputStream. If the current file type is ASCII, line separators in the file are converted to the local representation.

      Note: if you have used `setRestartOffset(long)`, the file data will start from the selected offset.

      Parameters:
        `remote` - The name of the remote file.
        `local` - The local OutputStream to which to write the file.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `CopyStreamException` - If an I/O error occurs while actually transferring the file. The CopyStreamException allows you to determine the number of bytes transferred and the IOException causing the error. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### _retrieveFile

          protected boolean _retrieveFile(String command,
                              String remote,
                              OutputStream local)
                                   throws IOException

      Throws:
        `IOException`
      Since:
        3.1

    - #### retrieveFileStream

          public InputStream retrieveFileStream(String remote)
                                         throws IOException

      Returns an InputStream from which a named file from the server can be read. If the current file type is ASCII, the returned InputStream will convert line separators in the file to the local representation. You must close the InputStream when you finish reading from it. The InputStream itself will take care of closing the parent data connection socket upon being closed. To finalize the file transfer you must call `completePendingCommand` and check its return value to verify success.

      Note: if you have used `setRestartOffset(long)`, the file data will start from the selected offset.

      Parameters:
        `remote` - The name of the remote file.
      Returns:
        An InputStream from which the remote file can be read. If the data connection cannot be opened (e.g., the file does not exist), null is returned (in which case you may check the reply code to determine the exact reason for failure).
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### _retrieveFileStream

          protected InputStream _retrieveFileStream(String command,
                                        String remote)
                                             throws IOException

      Throws:
        `IOException`
      Since:
        3.1

    - #### storeFile

          public boolean storeFile(String remote,
                          InputStream local)
                            throws IOException

      Stores a file on the server using the given name and taking input from the given InputStream. This method does NOT close the given InputStream. If the current file type is ASCII, line separators in the file are transparently converted to the NETASCII format (i.e., you should not attempt to create a special InputStream to do this).

      Parameters:
        `remote` - The name to give the remote file.
        `local` - The local InputStream from which to read the file.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `CopyStreamException` - If an I/O error occurs while actually transferring the file. The CopyStreamException allows you to determine the number of bytes transferred and the IOException causing the error. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### storeFileStream

          public OutputStream storeFileStream(String remote)
                                       throws IOException

      Returns an OutputStream through which data can be written to store a file on the server using the given name. If the current file type is ASCII, the returned OutputStream will convert line separators in the file to the NETASCII format (i.e., you should not attempt to create a special OutputStream to do this). You must close the OutputStream when you finish writing to it. The OutputStream itself will take care of closing the parent data connection socket upon being closed. To finalize the file transfer you must call `completePendingCommand` and check its return value to verify success.

      Parameters:
        `remote` - The name to give the remote file.
      Returns:
        An OutputStream through which the remote file can be written. If the data connection cannot be opened (e.g., the file does not exist), null is returned (in which case you may check the reply code to determine the exact reason for failure).
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### appendFile

          public boolean appendFile(String remote,
                           InputStream local)
                             throws IOException

      Appends to a file on the server with the given name, taking input from the given InputStream. This method does NOT close the given InputStream. If the current file type is ASCII, line separators in the file are transparently converted to the NETASCII format (i.e., you should not attempt to create a special InputStream to do this).

      Parameters:
        `remote` - The name of the remote file.
        `local` - The local InputStream from which to read the data to be appended to the remote file.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `CopyStreamException` - If an I/O error occurs while actually transferring the file. The CopyStreamException allows you to determine the number of bytes transferred and the IOException causing the error. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### appendFileStream

          public OutputStream appendFileStream(String remote)
                                        throws IOException

      Returns an OutputStream through which data can be written to append to a file on the server with the given name. If the current file type is ASCII, the returned OutputStream will convert line separators in the file to the NETASCII format (i.e., you should not attempt to create a special OutputStream to do this). You must close the OutputStream when you finish writing to it. The OutputStream itself will take care of closing the parent data connection socket upon being closed. To finalize the file transfer you must call `completePendingCommand` and check its return value to verify success.

      Parameters:
        `remote` - The name of the remote file.
      Returns:
        An OutputStream through which the remote file can be appended. If the data connection cannot be opened (e.g., the file does not exist), null is returned (in which case you may check the reply code to determine the exact reason for failure).
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### storeUniqueFile

          public boolean storeUniqueFile(String remote,
                                InputStream local)
                                  throws IOException

      Stores a file on the server using a unique name derived from the given name and taking input from the given InputStream. This method does NOT close the given InputStream. If the current file type is ASCII, line separators in the file are transparently converted to the NETASCII format (i.e., you should not attempt to create a special InputStream to do this).

      Parameters:
        `remote` - The name on which to base the unique name given to the remote file.
        `local` - The local InputStream from which to read the file.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `CopyStreamException` - If an I/O error occurs while actually transferring the file. The CopyStreamException allows you to determine the number of bytes transferred and the IOException causing the error. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### storeUniqueFileStream

          public OutputStream storeUniqueFileStream(String remote)
                                             throws IOException

      Returns an OutputStream through which data can be written to store a file on the server using a unique name derived from the given name. If the current file type is ASCII, the returned OutputStream will convert line separators in the file to the NETASCII format (i.e., you should not attempt to create a special OutputStream to do this). You must close the OutputStream when you finish writing to it. The OutputStream itself will take care of closing the parent data connection socket upon being closed. To finalize the file transfer you must call `completePendingCommand` and check its return value to verify success.

      Parameters:
        `remote` - The name on which to base the unique name given to the remote file.
      Returns:
        An OutputStream through which the remote file can be written. If the data connection cannot be opened (e.g., the file does not exist), null is returned (in which case you may check the reply code to determine the exact reason for failure).
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### storeUniqueFile

          public boolean storeUniqueFile(InputStream local)
                                  throws IOException

      Stores a file on the server using a unique name assigned by the server and taking input from the given InputStream. This method does NOT close the given InputStream. If the current file type is ASCII, line separators in the file are transparently converted to the NETASCII format (i.e., you should not attempt to create a special InputStream to do this).

      Parameters:
        `local` - The local InputStream from which to read the file.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `CopyStreamException` - If an I/O error occurs while actually transferring the file. The CopyStreamException allows you to determine the number of bytes transferred and the IOException causing the error. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### storeUniqueFileStream

          public OutputStream storeUniqueFileStream()
                                             throws IOException

      Returns an OutputStream through which data can be written to store a file on the server using a unique name assigned by the server. If the current file type is ASCII, the returned OutputStream will convert line separators in the file to the NETASCII format (i.e., you should not attempt to create a special OutputStream to do this). You must close the OutputStream when you finish writing to it. The OutputStream itself will take care of closing the parent data connection socket upon being closed. To finalize the file transfer you must call `completePendingCommand` and check its return value to verify success.

      Returns:
        An OutputStream through which the remote file can be written. If the data connection cannot be opened (e.g., the file does not exist), null is returned (in which case you may check the reply code to determine the exact reason for failure).
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### allocate

          public boolean allocate(int bytes)
                           throws IOException

      Reserve a number of bytes on the server for the next file transfer.

      Parameters:
        `bytes` - The number of bytes which the server should allocate.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### features

          public boolean features()
                           throws IOException

      Query the server for supported features. The server may reply with a list of server-supported exensions. For example, a typical client-server interaction might be (from RFC 2389):

                  C> feat
                  S> 211-Extensions supported:
                  S>  MLST size*;create;modify*;perm;media-type
                  S>  SIZE
                  S>  COMPRESSION
                  S>  MDTM
                  S> 211 END

      Returns:
        True if successfully completed, false if not.
      Throws:
        `IOException`
      Since:
        2.2
      See Also:
        http://www.faqs.org/rfcs/rfc2389.html

    - #### featureValues

          public String[] featureValues(String feature)
                                 throws IOException

      Query the server for a supported feature, and returns its values (if any). Caches the parsed response to avoid resending the command repeatedly.
      Returns:
        if the feature is present, returns the feature values (empty array if none) Returns `null` if the feature is not found or the command failed. Check `FTP.getReplyCode()` or `FTP.getReplyString()` if so.
      Throws:
        `IOException`
      Since:
        3.0

    - #### featureValue

          public String featureValue(String feature)
                              throws IOException

      Query the server for a supported feature, and returns the its value (if any). Caches the parsed response to avoid resending the command repeatedly.
      Returns:
        if the feature is present, returns the feature value or the empty string if the feature exists but has no value. Returns `null` if the feature is not found or the command failed. Check `FTP.getReplyCode()` or `FTP.getReplyString()` if so.
      Throws:
        `IOException`
      Since:
        3.0

    - #### hasFeature

          public boolean hasFeature(String feature)
                             throws IOException

      Query the server for a supported feature. Caches the parsed response to avoid resending the command repeatedly.
      Parameters:
        `feature` - the name of the feature; it is converted to upper case.
      Returns:
        `true` if the feature is present, `false` if the feature is not present or the `FTP.feat()` command failed. Check `FTP.getReplyCode()` or `FTP.getReplyString()` if it is necessary to distinguish these cases.
      Throws:
        `IOException`
      Since:
        3.0

    - #### hasFeature

          public boolean hasFeature(String feature,
                           String value)
                             throws IOException

      Query the server for a supported feature with particular value, for example "AUTH SSL" or "AUTH TLS". Caches the parsed response to avoid resending the command repeatedly.
      Parameters:
        `feature` - the name of the feature; it is converted to upper case.
        `value` - the value to find.
      Returns:
        `true` if the feature is present, `false` if the feature is not present or the `FTP.feat()` command failed. Check `FTP.getReplyCode()` or `FTP.getReplyString()` if it is necessary to distinguish these cases.
      Throws:
        `IOException`
      Since:
        3.0

    - #### allocate

          public boolean allocate(int bytes,
                         int recordSize)
                           throws IOException

      Reserve space on the server for the next file transfer.

      Parameters:
        `bytes` - The number of bytes which the server should allocate.
        `recordSize` - The size of a file record.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### doCommand

          public boolean doCommand(String command,
                          String params)
                            throws IOException

      Issue a command and wait for the reply.

      Should only be used with commands that return replies on the command channel - do not use for LIST, NLST, MLSD etc.

      Parameters:
        `command` - The command to invoke
        `params` - The parameters string, may be `null`
      Returns:
        True if successfully completed, false if not, in which case call `FTP.getReplyCode()` or `FTP.getReplyString()` to get the reason.
      Throws:
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
      Since:
        3.0

    - #### doCommandAsStrings

          public String[] doCommandAsStrings(String command,
                                    String params)
                                      throws IOException

      Issue a command and wait for the reply, returning it as an array of strings.

      Should only be used with commands that return replies on the command channel - do not use for LIST, NLST, MLSD etc.

      Parameters:
        `command` - The command to invoke
        `params` - The parameters string, may be `null`
      Returns:
        The array of replies, or `null` if the command failed, in which case call `FTP.getReplyCode()` or `FTP.getReplyString()` to get the reason.
      Throws:
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
      Since:
        3.0

    - #### mlistFile

          public FTPFile mlistFile(String pathname)
                            throws IOException

      Get file details using the MLST command
      Parameters:
        `pathname` - the file or directory to list, may be `` null
      Returns:
        the file details, may be `null`
      Throws:
        `IOException`
      Since:
        3.0

    - #### mlistDir

          public FTPFile[] mlistDir()
                             throws IOException

      Generate a directory listing for the current directory using the MLSD command.
      Returns:
        the array of file entries
      Throws:
        `IOException`
      Since:
        3.0

    - #### mlistDir

          public FTPFile[] mlistDir(String pathname)
                             throws IOException

      Generate a directory listing using the MLSD command.
      Parameters:
        `pathname` - the directory name, may be `null`
      Returns:
        the array of file entries
      Throws:
        `IOException`
      Since:
        3.0

    - #### mlistDir

          public FTPFile[] mlistDir(String pathname,
                           FTPFileFilter filter)
                             throws IOException

      Generate a directory listing using the MLSD command.
      Parameters:
        `pathname` - the directory name, may be `null`
        `filter` - the filter to apply to the responses
      Returns:
        the array of file entries
      Throws:
        `IOException`
      Since:
        3.0

    - #### restart

          protected boolean restart(long offset)
                             throws IOException

      Restart a `STREAM_TRANSFER_MODE` file transfer starting from the given offset. This will only work on FTP servers supporting the REST comand for the stream transfer mode. However, most FTP servers support this. Any subsequent file transfer will start reading or writing the remote file from the indicated offset.

      Parameters:
        `offset` - The offset into the remote file at which to start the next file transfer.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
      Since:
        3.1 (changed from private to protected)

    - #### setRestartOffset

          public void setRestartOffset(long offset)

      Sets the restart offset for file transfers.

      The restart command is not sent to the server immediately. It is sent when a data connection is created as part of a subsequent command. The restart marker is reset to zero after use.

      Note: This method should only be invoked immediately prior to the transfer to which it applies.

      Parameters:
        `offset` - The offset into the remote file at which to start the next file transfer. This must be a value greater than or equal to zero.

    - #### getRestartOffset

          public long getRestartOffset()

      Fetches the restart offset.

      Returns:
        offset The offset into the remote file at which to start the next file transfer.

    - #### rename

          public boolean rename(String from,
                       String to)
                         throws IOException

      Renames a remote file.

      Parameters:
        `from` - The name of the remote file to rename.
        `to` - The new name of the remote file.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### abort

          public boolean abort()
                        throws IOException

      Abort a transfer in progress.

      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### deleteFile

          public boolean deleteFile(String pathname)
                             throws IOException

      Deletes a file on the FTP server.

      Parameters:
        `pathname` - The pathname of the file to be deleted.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### removeDirectory

          public boolean removeDirectory(String pathname)
                                  throws IOException

      Removes a directory on the FTP server (if empty).

      Parameters:
        `pathname` - The pathname of the directory to remove.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### makeDirectory

          public boolean makeDirectory(String pathname)
                                throws IOException

      Creates a new subdirectory on the FTP server in the current directory (if a relative pathname is given) or where specified (if an absolute pathname is given).

      Parameters:
        `pathname` - The pathname of the directory to create.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### printWorkingDirectory

          public String printWorkingDirectory()
                                       throws IOException

      Returns the pathname of the current working directory.

      Returns:
        The pathname of the current working directory. If it cannot be obtained, returns null.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### sendSiteCommand

          public boolean sendSiteCommand(String arguments)
                                  throws IOException

      Send a site specific command.
      Parameters:
        `arguments` - The site specific command and arguments.
      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### getSystemType

          public String getSystemType()
                               throws IOException

      Fetches the system type from the server and returns the string. This value is cached for the duration of the connection after the first call to this method. In other words, only the first time that you invoke this method will it issue a SYST command to the FTP server. FTPClient will remember the value and return the cached value until a call to disconnect.

      If the SYST command fails, and the system property `FTP_SYSTEM_TYPE_DEFAULT` is defined, then this is used instead.

      Returns:
        The system type obtained from the server. Never null.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server (and the default system type property is not defined)
      Since:
        2.2

    - #### listHelp

          public String listHelp()
                          throws IOException

      Fetches the system help information from the server and returns the full string.

      Returns:
        The system help string obtained from the server. null if the information could not be obtained.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### listHelp

          public String listHelp(String command)
                          throws IOException

      Fetches the help information for a given command from the server and returns the full string.
      Parameters:
        `command` - The command on which to ask for help.
      Returns:
        The command help string obtained from the server. null if the information could not be obtained.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### sendNoOp

          public boolean sendNoOp()
                           throws IOException

      Sends a NOOP command to the FTP server. This is useful for preventing server timeouts.

      Returns:
        True if successfully completed, false if not.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### listNames

          public String[] listNames(String pathname)
                             throws IOException

      Obtain a list of filenames in a directory (or just the name of a given file, which is not particularly useful). This information is obtained through the NLST command. If the given pathname is a directory and contains no files, a zero length array is returned only if the FTP server returned a positive completion code, otherwise null is returned (the FTP server returned a 550 error No files found.). If the directory is not empty, an array of filenames in the directory is returned. If the pathname corresponds to a file, only that file will be listed. The server may or may not expand glob expressions.

      Parameters:
        `pathname` - The file or directory to list. Warning: the server may treat a leading '-' as an option introducer. If so, try using an absolute path, or prefix the path with ./ (unix style servers). Some servers may support "--" as meaning end of options, in which case "-- -xyz" should work.
      Returns:
        The list of filenames contained in the given path. null if the list could not be obtained. If there are no filenames in the directory, a zero-length array is returned.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### listNames

          public String[] listNames()
                             throws IOException

      Obtain a list of filenames in the current working directory This information is obtained through the NLST command. If the current directory contains no files, a zero length array is returned only if the FTP server returned a positive completion code, otherwise, null is returned (the FTP server returned a 550 error No files found.). If the directory is not empty, an array of filenames in the directory is returned.

      Returns:
        The list of filenames contained in the current working directory. null if the list could not be obtained. If there are no filenames in the directory, a zero-length array is returned.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### listFiles

          public FTPFile[] listFiles(String pathname)
                              throws IOException

      Using the default system autodetect mechanism, obtain a list of file information for the current working directory or for just a single file.

      This information is obtained through the LIST command. The contents of the returned array is determined by the`FTPFileEntryParser` used.

      Parameters:
        `pathname` - The file or directory to list. Since the server may or may not expand glob expressions, using them here is not recommended and may well cause this method to fail. Also, some servers treat a leading '-' as being an option. To avoid this interpretation, use an absolute pathname or prefix the pathname with ./ (unix style servers). Some servers may support "--" as meaning end of options, in which case "-- -xyz" should work.
      Returns:
        The list of file information contained in the given path in the format determined by the autodetection mechanism
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
        `ParserInitializationException` - Thrown if the parserKey parameter cannot be resolved by the selected parser factory. In the DefaultFTPEntryParserFactory, this will happen when parserKey is neither the fully qualified class name of a class implementing the interface org.apache.commons.net.ftp.FTPFileEntryParser nor a string containing one of the recognized keys mapping to such a parser or if class loader security issues prevent its being loaded.
      See Also:
        `DefaultFTPFileEntryParserFactory`, `FTPFileEntryParserFactory`, `FTPFileEntryParser`

    - #### listFiles

          public FTPFile[] listFiles()
                              throws IOException

      Using the default system autodetect mechanism, obtain a list of file information for the current working directory.

      This information is obtained through the LIST command. The contents of the returned array is determined by the`FTPFileEntryParser` used.

      Returns:
        The list of file information contained in the current directory in the format determined by the autodetection mechanism.

        NOTE: This array may contain null members if any of the individual file listings failed to parse. The caller should check each entry for null before referencing it.

      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
        `ParserInitializationException` - Thrown if the parserKey parameter cannot be resolved by the selected parser factory. In the DefaultFTPEntryParserFactory, this will happen when parserKey is neither the fully qualified class name of a class implementing the interface org.apache.commons.net.ftp.FTPFileEntryParser nor a string containing one of the recognized keys mapping to such a parser or if class loader security issues prevent its being loaded.
      See Also:
        `DefaultFTPFileEntryParserFactory`, `FTPFileEntryParserFactory`, `FTPFileEntryParser`

    - #### listFiles

          public FTPFile[] listFiles(String pathname,
                            FTPFileFilter filter)
                              throws IOException

      Version of `listFiles(String)` which allows a filter to be provided. For example: `listFiles("site", FTPFileFilters.DIRECTORY);`
      Parameters:
        `pathname` - the initial path, may be null
        `filter` - the filter, non-null
      Returns:
        the list of FTPFile entries.
      Throws:
        `IOException`
      Since:
        2.2

    - #### listDirectories

          public FTPFile[] listDirectories()
                                    throws IOException

      Using the default system autodetect mechanism, obtain a list of directories contained in the current working directory.

      This information is obtained through the LIST command. The contents of the returned array is determined by the`FTPFileEntryParser` used.

      Returns:
        The list of directories contained in the current directory in the format determined by the autodetection mechanism.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
        `ParserInitializationException` - Thrown if the parserKey parameter cannot be resolved by the selected parser factory. In the DefaultFTPEntryParserFactory, this will happen when parserKey is neither the fully qualified class name of a class implementing the interface org.apache.commons.net.ftp.FTPFileEntryParser nor a string containing one of the recognized keys mapping to such a parser or if class loader security issues prevent its being loaded.
      Since:
        3.0
      See Also:
        `DefaultFTPFileEntryParserFactory`, `FTPFileEntryParserFactory`, `FTPFileEntryParser`

    - #### listDirectories

          public FTPFile[] listDirectories(String parent)
                                    throws IOException

      Using the default system autodetect mechanism, obtain a list of directories contained in the specified directory.

      This information is obtained through the LIST command. The contents of the returned array is determined by the`FTPFileEntryParser` used.

      Returns:
        The list of directories contained in the specified directory in the format determined by the autodetection mechanism.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
        `ParserInitializationException` - Thrown if the parserKey parameter cannot be resolved by the selected parser factory. In the DefaultFTPEntryParserFactory, this will happen when parserKey is neither the fully qualified class name of a class implementing the interface org.apache.commons.net.ftp.FTPFileEntryParser nor a string containing one of the recognized keys mapping to such a parser or if class loader security issues prevent its being loaded.
      Since:
        3.0
      See Also:
        `DefaultFTPFileEntryParserFactory`, `FTPFileEntryParserFactory`, `FTPFileEntryParser`

    - #### initiateListParsing

          public FTPListParseEngine initiateListParsing()
                                                 throws IOException

      Using the default autodetect mechanism, initialize an FTPListParseEngine object containing a raw file information for the current working directory on the server This information is obtained through the LIST command. This object is then capable of being iterated to return a sequence of FTPFile objects with information filled in by the `FTPFileEntryParser` used.

      This method differs from using the listFiles() methods in that expensive FTPFile objects are not created until needed which may be an advantage on large lists.

      Returns:
        A FTPListParseEngine object that holds the raw information and is capable of providing parsed FTPFile objects, one for each file containing information contained in the given path in the format determined by the `parser` parameter. Null will be returned if a data connection cannot be opened. If the current working directory contains no files, an empty array will be the return.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
        `ParserInitializationException` - Thrown if the autodetect mechanism cannot resolve the type of system we are connected with.
      See Also:
        `FTPListParseEngine`

    - #### initiateListParsing

          public FTPListParseEngine initiateListParsing(String pathname)
                                                 throws IOException

      Using the default autodetect mechanism, initialize an FTPListParseEngine object containing a raw file information for the supplied directory. This information is obtained through the LIST command. This object is then capable of being iterated to return a sequence of FTPFile objects with information filled in by the `FTPFileEntryParser` used.

      The server may or may not expand glob expressions. You should avoid using glob expressions because the return format for glob listings differs from server to server and will likely cause this method to fail.

      This method differs from using the listFiles() methods in that expensive FTPFile objects are not created until needed which may be an advantage on large lists.

              FTPClient f=FTPClient();
              f.connect(server);
              f.login(username, password);
              FTPListParseEngine engine = f.initiateListParsing(directory);

              while (engine.hasNext()) {
                 FTPFile[] files = engine.getNext(25);  // "page size" you want
                 //do whatever you want with these files, display them, etc.
                 //expensive FTPFile objects not created until needed.
              }

      Returns:
        A FTPListParseEngine object that holds the raw information and is capable of providing parsed FTPFile objects, one for each file containing information contained in the given path in the format determined by the `parser` parameter. Null will be returned if a data connection cannot be opened. If the current working directory contains no files, an empty array will be the return.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
        `ParserInitializationException` - Thrown if the autodetect mechanism cannot resolve the type of system we are connected with.
      See Also:
        `FTPListParseEngine`

    - #### initiateListParsing

          public FTPListParseEngine initiateListParsing(String parserKey,
                                               String pathname)
                                                 throws IOException

      Using the supplied parser key, initialize an FTPListParseEngine object containing a raw file information for the supplied directory. This information is obtained through the LIST command. This object is then capable of being iterated to return a sequence of FTPFile objects with information filled in by the `FTPFileEntryParser` used.

      The server may or may not expand glob expressions. You should avoid using glob expressions because the return format for glob listings differs from server to server and will likely cause this method to fail.

      This method differs from using the listFiles() methods in that expensive FTPFile objects are not created until needed which may be an advantage on large lists.

      Parameters:
        `parserKey` - A string representing a designated code or fully-qualified class name of an `FTPFileEntryParser` that should be used to parse each server file listing. May be `null`, in which case the code checks first the system property `FTP_SYSTEM_TYPE`, and if that is not defined the SYST command is used to provide the value. To allow for arbitrary system types, the return from the SYST command is used to look up an alias for the type in the `SYSTEM_TYPE_PROPERTIES` properties file if it is available.
      Returns:
        A FTPListParseEngine object that holds the raw information and is capable of providing parsed FTPFile objects, one for each file containing information contained in the given path in the format determined by the `parser` parameter. Null will be returned if a data connection cannot be opened. If the current working directory contains no files, an empty array will be the return.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.
        `ParserInitializationException` - Thrown if the parserKey parameter cannot be resolved by the selected parser factory. In the DefaultFTPEntryParserFactory, this will happen when parserKey is neither the fully qualified class name of a class implementing the interface org.apache.commons.net.ftp.FTPFileEntryParser nor a string containing one of the recognized keys mapping to such a parser or if class loader security issues prevent its being loaded.
      See Also:
        `FTPListParseEngine`

    - #### getListArguments

          protected String getListArguments(String pathname)

      Since:
        2.0

    - #### getStatus

          public String getStatus()
                           throws IOException

      Issue the FTP STAT command to the server.

      Returns:
        The status information returned by the server.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### getStatus

          public String getStatus(String pathname)
                           throws IOException

      Issue the FTP STAT command to the server for a given pathname. This should produce a listing of the file or directory.

      Returns:
        The status information returned by the server.
      Throws:
        `FTPConnectionClosedException` - If the FTP server prematurely closes the connection as a result of the client being idle or some other reason causing the server to send FTP reply code 421. This exception may be caught either as an IOException or independently as itself.
        `IOException` - If an I/O error occurs while either sending a command to the server or receiving a reply from the server.

    - #### getModificationTime

          public String getModificationTime(String pathname)
                                     throws IOException

      Issue the FTP MDTM command (not supported by all servers to retrieve the last modification time of a file. The modification string should be in the ISO 3077 form "YYYYMMDDhhmmss(.xxx)?". The timestamp represented should also be in GMT, but not all FTP servers honour this.
      Parameters:
        `pathname` - The file path to query.
      Returns:
        A string representing the last file modification time in `YYYYMMDDhhmmss` format.
      Throws:
        `IOException` - if an I/O error occurs.
      Since:
        2.0

    - #### setModificationTime

          public boolean setModificationTime(String pathname,
                                    String timeval)
                                      throws IOException

      Issue the FTP MFMT command (not supported by all servers) which sets the last modified time of a file. The timestamp should be in the form `YYYYMMDDhhmmss`. It should also be in GMT, but not all servers honour this. An FTP server would indicate its support of this feature by including "MFMT" in its response to the FEAT command, which may be retrieved by FTPClient.features()
      Parameters:
        `pathname` - The file path for which last modified time is to be changed.
        `timeval` - The timestamp to set to, in `YYYYMMDDhhmmss` format.
      Returns:
        true if successfully set, false if not
      Throws:
        `IOException` - if an I/O error occurs.
      Since:
        2.2
      See Also:
        http://tools.ietf.org/html/draft-somers-ftp-mfxx-04

    - #### setBufferSize

          public void setBufferSize(int bufSize)

      Set the internal buffer size for buffered data streams.
      Parameters:
        `bufSize` - The size of the buffer. Use a non-positive value to use the default.

    - #### getBufferSize

          public int getBufferSize()

      Retrieve the current internal buffer size for buffered data streams.
      Returns:
        The current buffer size.

    - #### setSendDataSocketBufferSize

          public void setSendDataSocketBufferSize(int bufSize)

      Sets the value to be used for the data socket SO_SNDBUF option. If the value is positive, the option will be set when the data socket has been created.
      Parameters:
        `bufSize` - The size of the buffer, zero or negative means the value is ignored.
      Since:
        3.3

    - #### getSendDataSocketBufferSize

          public int getSendDataSocketBufferSize()

      Retrieve the value to be used for the data socket SO_SNDBUF option.
      Returns:
        The current buffer size.
      Since:
        3.3

    - #### setReceieveDataSocketBufferSize

          public void setReceieveDataSocketBufferSize(int bufSize)

      Sets the value to be used for the data socket SO_RCVBUF option. If the value is positive, the option will be set when the data socket has been created.
      Parameters:
        `bufSize` - The size of the buffer, zero or negative means the value is ignored.
      Since:
        3.3

    - #### getReceiveDataSocketBufferSize

          public int getReceiveDataSocketBufferSize()

      Retrieve the value to be used for the data socket SO_RCVBUF option.
      Returns:
        The current buffer size.
      Since:
        3.3

    - #### configure

          public void configure(FTPClientConfig config)

      Implementation of the `Configurable` interface. In the case of this class, configuring merely makes the config object available for the factory methods that construct parsers.
      Specified by:
        `configure` in interface `Configurable`
      Parameters:
        `config` - `FTPClientConfig` object used to provide non-standard configurations to the parser.
      Since:
        1.4

    - #### setListHiddenFiles

          public void setListHiddenFiles(boolean listHiddenFiles)

      You can set this to true if you would like to get hidden files when `listFiles(java.lang.String)` too. A `LIST -a` will be issued to the ftp server. It depends on your ftp server if you need to call this method, also dont expect to get rid of hidden files if you call this method with "false".
      Parameters:
        `listHiddenFiles` - true if hidden files should be listed
      Since:
        2.0

    - #### getListHiddenFiles

          public boolean getListHiddenFiles()

      Returns:
        the current state
      Since:
        2.0
      See Also:
        `setListHiddenFiles(boolean)`

    - #### isUseEPSVwithIPv4

          public boolean isUseEPSVwithIPv4()

      Whether should attempt to use EPSV with IPv4. Default (if not set) is `false`
      Returns:
        true if should attempt EPSV
      Since:
        2.2

    - #### setUseEPSVwithIPv4

          public void setUseEPSVwithIPv4(boolean selected)

      Set whether to use EPSV with IPv4. Might be worth enabling in some circumstances. For example, when using IPv4 with NAT it may work with some rare configurations. E.g. if FTP server has a static PASV address (external network) and the client is coming from another internal network. In that case the data connection after PASV command would fail, while EPSV would make the client succeed by taking just the port.
      Parameters:
        `selected` - value to set.
      Since:
        2.2

    - #### setCopyStreamListener

          public void setCopyStreamListener(CopyStreamListener listener)

      Set the listener to be used when performing store/retrieve operations. The default value (if not set) is `null`.
      Parameters:
        `listener` - to be used, may be `null` to disable
      Since:
        3.0

    - #### getCopyStreamListener

          public CopyStreamListener getCopyStreamListener()

      Obtain the currently active listener.
      Returns:
        the listener, may be `null`
      Since:
        3.0

    - #### setControlKeepAliveTimeout

          public void setControlKeepAliveTimeout(long controlIdle)

      Set the time to wait between sending control connection keepalive messages when processing file upload or download.
      Parameters:
        `controlIdle` - the wait (in secs) between keepalive messages. Zero (or less) disables.
      Since:
        3.0
      See Also:
        `setControlKeepAliveReplyTimeout(int)`

    - #### getControlKeepAliveTimeout

          public long getControlKeepAliveTimeout()

      Get the time to wait between sending control connection keepalive messages.
      Returns:
        the number of seconds between keepalive messages.
      Since:
        3.0

    - #### setControlKeepAliveReplyTimeout

          public void setControlKeepAliveReplyTimeout(int timeout)

      Set how long to wait for control keep-alive message replies.
      Parameters:
        `timeout` - number of milliseconds to wait (defaults to 1000)
      Since:
        3.0
      See Also:
        `setControlKeepAliveTimeout(long)`

    - #### getControlKeepAliveReplyTimeout

          public int getControlKeepAliveReplyTimeout()

      Get how long to wait for control keep-alive message replies.
      Since:
        3.0

    - #### setPassiveNatWorkaround

          public void setPassiveNatWorkaround(boolean enabled)

      Enable or disable passive mode NAT workaround. If enabled, a site-local PASV mode reply address will be replaced with the remote host address to which the PASV mode request was sent (unless that is also a site local address). This gets around the problem that some NAT boxes may change the reply. The default is true, i.e. site-local replies are replaced.
      Parameters:
        `enabled` - true to enable replacing internal IP's in passive mode.

    - #### setAutodetectUTF8

          public void setAutodetectUTF8(boolean autodetect)

      Enables or disables automatic server encoding detection (only UTF-8 supported).

      Does not affect existing connections; must be invoked before a connection is established.

      Parameters:
        `autodetect` - If true, automatic server encoding detection will be enabled.

    - #### getAutodetectUTF8

          public boolean getAutodetectUTF8()

      Tells if automatic server encoding detection is enabled or disabled.
      Returns:
        true, if automatic server encoding detection is enabled.

    - #### getSystemName

          @Deprecated
          public String getSystemName()
                               throws IOException

      Deprecated. use `getSystemType()` instead
      Throws:
        `IOException`

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