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## org.apache.commons.net
Class SocketClient

    java.lang.Object
      org.apache.commons.net.SocketClient

Direct Known Subclasses:
  CharGenTCPClient, DaytimeTCPClient, DiscardTCPClient, FingerClient, NNTP, POP3, RExecClient, SMTP, org.apache.commons.net.telnet.Telnet, TimeTCPClient

public abstract class SocketClient
extends Object

The SocketClient provides the basic operations that are required of client objects accessing sockets. It is meant to be subclassed to avoid having to rewrite the same code over and over again to open a socket, close a socket, set timeouts, etc. Of special note is the `setSocketFactory` method, which allows you to control the type of Socket the SocketClient creates for initiating network connections. This is especially useful for adding SSL or proxy support as well as better support for applets. For example, you could create a `SocketFactory` that requests browser security capabilities before creating a socket. All classes derived from SocketClient should use the `_socketFactory_` member variable to create Socket and ServerSocket instances rather than instanting them by directly invoking a constructor. By honoring this contract you guarantee that a user will always be able to provide his own Socket implementations by substituting his own SocketFactory.

Author:
  Daniel F. Savarese
See Also:
  `SocketFactory`

Field Summary
`protected int` | `_defaultPort_` The default port the client should connect to.
`protected InputStream` | `_input_` The socket's InputStream.
`protected boolean` | `_isConnected_` A status variable indicating if the client's socket is currently open.
`protected OutputStream` | `_output_` The socket's OutputStream.
`protected Socket` | `_socket_` The socket used for the connection.
`protected SocketFactory` | `_socketFactory_` The socket's SocketFactory.
`protected int` | `_timeout_` The timeout to use after opening a socket.
`static String` | `NETASCII_EOL` The end of line character sequence used by most IETF protocols.

Constructor Summary
`SocketClient()` Default constructor for SocketClient.

Method Summary
`protected void` | `_connectAction_()` Because there are so many connect() methods, the _connectAction_() method is provided as a means of performing some action immediately after establishing a connection, rather than reimplementing all of the connect() methods.
`void` | `connect(InetAddress host)` Opens a Socket connected to a remote host at the current default port and originating from the current host at a system assigned port.
`void` | `connect(InetAddress host, int port)` Opens a Socket connected to a remote host at the specified port and originating from the current host at a system assigned port.
`void` | `connect(InetAddress host, int port, InetAddress localAddr, int localPort)` Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port.
`void` | `connect(String hostname)` Opens a Socket connected to a remote host at the current default port and originating from the current host at a system assigned port.
`void` | `connect(String hostname, int port)` Opens a Socket connected to a remote host at the specified port and originating from the current host at a system assigned port.
`void` | `connect(String hostname, int port, InetAddress localAddr, int localPort)` Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port.
`void` | `disconnect()` Disconnects the socket connection.
`int` | `getDefaultPort()` Returns the current value of the default port (stored in `_defaultPort_` ).
`int` | `getDefaultTimeout()` Returns the default timeout in milliseconds that is used when opening a socket.
`InetAddress` | `getLocalAddress()` Returns the local address to which the client's socket is bound.
`int` | `getLocalPort()` Returns the port number of the open socket on the local host used for the connection.
`InetAddress` | `getRemoteAddress()`
`int` | `getRemotePort()` Returns the port number of the remote host to which the client is connected.
`int` | `getSoLinger()` Returns the current SO_LINGER timeout of the currently opened socket.
`int` | `getSoTimeout()` Returns the timeout in milliseconds of the currently opened socket.
`boolean` | `getTcpNoDelay()` Returns true if Nagle's algorithm is enabled on the currently opened socket.
`boolean` | `isConnected()` Returns true if the client is currently connected to a server.
`void` | `setDefaultPort(int port)` Sets the default port the SocketClient should connect to when a port is not specified.
`void` | `setDefaultTimeout(int timeout)` Set the default timeout in milliseconds to use when opening a socket.
`void` | `setSocketFactory(SocketFactory factory)` Sets the SocketFactory used by the SocketClient to open socket connections.
`void` | `setSoLinger(boolean on, int val)` Sets the SO_LINGER timeout on the currently opened socket.
`void` | `setSoTimeout(int timeout)` Set the timeout in milliseconds of a currently open connection.
`void` | `setTcpNoDelay(boolean on)` Enables or disables the Nagle's algorithm (TCP_NODELAY) on the currently opened socket.
`boolean` | `verifyRemote(Socket socket)` Verifies that the remote end of the given socket is connected to the the same host that the SocketClient is currently connected to.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### NETASCII_EOL

    public static final String NETASCII_EOL

  The end of line character sequence used by most IETF protocols. That is a carriage return followed by a newline: "\r\n"

  See Also:
    Constant Field Values

### _timeout_

    protected int _timeout_

  The timeout to use after opening a socket.

### _socket_

    protected Socket _socket_

  The socket used for the connection.

### _isConnected_

    protected boolean _isConnected_

  A status variable indicating if the client's socket is currently open.

### _defaultPort_

    protected int _defaultPort_

  The default port the client should connect to.

### _input_

    protected InputStream _input_

  The socket's InputStream.

### _output_

    protected OutputStream _output_

  The socket's OutputStream.

### _socketFactory_

    protected SocketFactory _socketFactory_

  The socket's SocketFactory.

Constructor Detail

### SocketClient

    public SocketClient()

  Default constructor for SocketClient. Initializes _socket_ to null, _timeout_ to 0, _defaultPort to 0, _isConnected_ to false, and _socketFactory_ to a shared instance of `DefaultSocketFactory`.

Method Detail

### _connectAction_

    protected void _connectAction_()
                            throws IOException

  Because there are so many connect() methods, the _connectAction_() method is provided as a means of performing some action immediately after establishing a connection, rather than reimplementing all of the connect() methods. The last action performed by every connect() method after opening a socket is to call this method.

  This method sets the timeout on the just opened socket to the default timeout set by `setDefaultTimeout()` , sets _input_ and _output_ to the socket's InputStream and OutputStream respectively, and sets _isConnected_ to true.

  Subclasses overriding this method should start by calling `super._connectAction_()` first to ensure the initialization of the aforementioned protected variables.

  Throws:
    `IOException`

### connect

    public void connect(InetAddress host,
                        int port)
                 throws SocketException,
                        IOException

  Opens a Socket connected to a remote host at the specified port and originating from the current host at a system assigned port. Before returning, `_connectAction_()` is called to perform connection initialization actions.

  Parameters:
    `host` - The remote host.
    `port` - The port to connect to on the remote host.
  Throws:
    `SocketException` - If the socket timeout could not be set.
    `IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.

### connect

    public void connect(String hostname,
                        int port)
                 throws SocketException,
                        IOException

  Opens a Socket connected to a remote host at the specified port and originating from the current host at a system assigned port. Before returning, `_connectAction_()` is called to perform connection initialization actions.

  Parameters:
    `hostname` - The name of the remote host.
    `port` - The port to connect to on the remote host.
  Throws:
    `SocketException` - If the socket timeout could not be set.
    `IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.
    `UnknownHostException` - If the hostname cannot be resolved.

### connect

    public void connect(InetAddress host,
                        int port,
                        InetAddress localAddr,
                        int localPort)
                 throws SocketException,
                        IOException

  Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port. Before returning, `_connectAction_()` is called to perform connection initialization actions.

  Parameters:
    `host` - The remote host.
    `port` - The port to connect to on the remote host.
    `localAddr` - The local address to use.
    `localPort` - The local port to use.
  Throws:
    `SocketException` - If the socket timeout could not be set.
    `IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.

### connect

    public void connect(String hostname,
                        int port,
                        InetAddress localAddr,
                        int localPort)
                 throws SocketException,
                        IOException

  Opens a Socket connected to a remote host at the specified port and originating from the specified local address and port. Before returning, `_connectAction_()` is called to perform connection initialization actions.

  Parameters:
    `hostname` - The name of the remote host.
    `port` - The port to connect to on the remote host.
    `localAddr` - The local address to use.
    `localPort` - The local port to use.
  Throws:
    `SocketException` - If the socket timeout could not be set.
    `IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.
    `UnknownHostException` - If the hostname cannot be resolved.

### connect

    public void connect(InetAddress host)
                 throws SocketException,
                        IOException

  Opens a Socket connected to a remote host at the current default port and originating from the current host at a system assigned port. Before returning, `_connectAction_()` is called to perform connection initialization actions.

  Parameters:
    `host` - The remote host.
  Throws:
    `SocketException` - If the socket timeout could not be set.
    `IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.

### connect

    public void connect(String hostname)
                 throws SocketException,
                        IOException

  Opens a Socket connected to a remote host at the current default port and originating from the current host at a system assigned port. Before returning, `_connectAction_()` is called to perform connection initialization actions.

  Parameters:
    `hostname` - The name of the remote host.
  Throws:
    `SocketException` - If the socket timeout could not be set.
    `IOException` - If the socket could not be opened. In most cases you will only want to catch IOException since SocketException is derived from it.
    `UnknownHostException` - If the hostname cannot be resolved.

### disconnect

    public void disconnect()
                    throws IOException

  Disconnects the socket connection. You should call this method after you've finished using the class instance and also before you call `connect()` again. _isConnected_ is set to false, _socket_ is set to null, _input_ is set to null, and _output_ is set to null.

  Throws:
    `IOException` - If there is an error closing the socket.

### isConnected

    public boolean isConnected()

  Returns true if the client is currently connected to a server.

  Returns:
    True if the client is currently connected to a server, false otherwise.

### setDefaultPort

    public void setDefaultPort(int port)

  Sets the default port the SocketClient should connect to when a port is not specified. The `_defaultPort_` variable stores this value. If never set, the default port is equal to zero.

  Parameters:
    `port` - The default port to set.

### getDefaultPort

    public int getDefaultPort()

  Returns the current value of the default port (stored in `_defaultPort_` ).

  Returns:
    The current value of the default port.

### setDefaultTimeout

    public void setDefaultTimeout(int timeout)

  Set the default timeout in milliseconds to use when opening a socket. This value is only used previous to a call to `connect()` and should not be confused with `setSoTimeout()` which operates on an the currently opened socket. _timeout_ contains the new timeout value.

  Parameters:
    `timeout` - The timeout in milliseconds to use for the socket connection.

### getDefaultTimeout

    public int getDefaultTimeout()

  Returns the default timeout in milliseconds that is used when opening a socket.

  Returns:
    The default timeout in milliseconds that is used when opening a socket.

### setSoTimeout

    public void setSoTimeout(int timeout)
                      throws SocketException

  Set the timeout in milliseconds of a currently open connection. Only call this method after a connection has been opened by `connect()`.

  Parameters:
    `timeout` - The timeout in milliseconds to use for the currently open socket connection.
  Throws:
    `SocketException` - If the operation fails.

### getSoTimeout

    public int getSoTimeout()
                     throws SocketException

  Returns the timeout in milliseconds of the currently opened socket.

  Returns:
    The timeout in milliseconds of the currently opened socket.
  Throws:
    `SocketException` - If the operation fails.

### setTcpNoDelay

    public void setTcpNoDelay(boolean on)
                       throws SocketException

  Enables or disables the Nagle's algorithm (TCP_NODELAY) on the currently opened socket.

  Parameters:
    `on` - True if Nagle's algorithm is to be enabled, false if not.
  Throws:
    `SocketException` - If the operation fails.

### getTcpNoDelay

    public boolean getTcpNoDelay()
                          throws SocketException

  Returns true if Nagle's algorithm is enabled on the currently opened socket.

  Returns:
    True if Nagle's algorithm is enabled on the currently opened socket, false otherwise.
  Throws:
    `SocketException` - If the operation fails.

### setSoLinger

    public void setSoLinger(boolean on,
                            int val)
                     throws SocketException

  Sets the SO_LINGER timeout on the currently opened socket.

  Parameters:
    `on` - True if linger is to be enabled, false if not.
    `val` - The linger timeout (in hundredths of a second?)
  Throws:
    `SocketException` - If the operation fails.

### getSoLinger

    public int getSoLinger()
                    throws SocketException

  Returns the current SO_LINGER timeout of the currently opened socket.

  Returns:
    The current SO_LINGER timeout. If SO_LINGER is disabled returns -1.
  Throws:
    `SocketException` - If the operation fails.

### getLocalPort

    public int getLocalPort()

  Returns the port number of the open socket on the local host used for the connection.

  Returns:
    The port number of the open socket on the local host used for the connection.

### getLocalAddress

    public InetAddress getLocalAddress()

  Returns the local address to which the client's socket is bound.

  Returns:
    The local address to which the client's socket is bound.

### getRemotePort

    public int getRemotePort()

  Returns the port number of the remote host to which the client is connected.

  Returns:
    The port number of the remote host to which the client is connected.

### getRemoteAddress

    public InetAddress getRemoteAddress()

  Returns:
    The remote address to which the client is connected.

### verifyRemote

    public boolean verifyRemote(Socket socket)

  Verifies that the remote end of the given socket is connected to the the same host that the SocketClient is currently connected to. This is useful for doing a quick security check when a client needs to accept a connection from a server, such as an FTP data connection or a BSD R command standard error stream.

  Returns:
    True if the remote hosts are the same, false if not.

### setSocketFactory

    public void setSocketFactory(SocketFactory factory)

  Sets the SocketFactory used by the SocketClient to open socket connections. If the factory value is null, then a default factory is used (only do this to reset the factory after having previously altered it).

  Parameters:
    `factory` - The new SocketFactory the SocketClient should use.

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