IO-158 New ReaderInputStream and WriterOutputStream implementations - thanks to Andreas Veithen for the patch

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/io/trunk@723912 13f79535-47bb-0310-9956-ffa450edef68

Author: Niall Pemberton

src/java/org/apache/commons/io/input/ReaderInputStream.java

@@ -0,0 +1,237 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.commons.io.input;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.Reader;
+import java.nio.ByteBuffer;
+import java.nio.CharBuffer;
+import java.nio.charset.Charset;
+import java.nio.charset.CharsetEncoder;
+import java.nio.charset.CoderResult;
+
+/**
+ * {@link InputStream} implementation that reads a character stream from a {@link Reader}
+ * and transforms it to a byte stream using a specified charset encoding. The stream
+ * is transformed using a {@link CharsetEncoder} object, guaranteeing that all charset
+ * encodings supported by the JRE are handled correctly. In particular for charsets such as
+ * UTF-16, the implementation ensures that one and only one byte order marker
+ * is produced.
+ * <p>
+ * Since in general it is not possible to predict the number of characters to be read from the
+ * {@link Reader} to satisfy a read request on the {@link ReaderInputStream}, all reads from
+ * the {@link Reader} are buffered. There is therefore no well defined correlation
+ * between the current position of the {@link Reader} and that of the {@link ReaderInputStream}.
+ * This also implies that in general there is no need to wrap the underlying {@link Reader}
+ * in a {@link java.io.BufferedReader}.
+ * <p>
+ * {@link ReaderInputStream} implements the inverse transformation of {@link java.io.InputStreamReader};
+ * in the following example, reading from <tt>in2</tt> would return the same byte
+ * sequence as reading from <tt>in</tt> (provided that the initial byte sequence is legal
+ * with respect to the charset encoding):
+ * <pre>
+ * InputStream in = ...
+ * Charset cs = ...
+ * InputStreamReader reader = new InputStreamReader(in, cs);
+ * ReaderInputStream in2 = new ReaderInputStream(reader, cs);</pre>
+ * {@link ReaderInputStream} implements the same transformation as {@link java.io.OutputStreamWriter},
+ * except that the control flow is reversed: both classes transform a character stream
+ * into a byte stream, but {@link java.io.OutputStreamWriter} pushes data to the underlying stream,
+ * while {@link ReaderInputStream} pulls it from the underlying stream.
+ * <p>
+ * Note that while there are use cases where there is no alternative to using
+ * this class, very often the need to use this class is an indication of a flaw
+ * in the design of the code. This class is typically used in situations where an existing
+ * API only accepts an {@link InputStream}, but where the most natural way to produce the data
+ * is as a character stream, i.e. by providing a {@link Reader} instance. An example of a situation
+ * where this problem may appear is when implementing the {@link javax.activation.DataSource}
+ * interface from the Java Activation Framework.
+ * <p>
+ * Given the fact that the {@link Reader} class doesn't provide any way to predict whether the next
+ * read operation will block or not, it is not possible to provide a meaningful
+ * implementation of the {@link InputStream#available()} method. A call to this method
+ * will always return 0. Also, this class doesn't support {@link InputStream#mark(int)}.
+ * <p>
+ * Instances of {@link ReaderInputStream} are not thread safe.
+ * 
+ * @see org.apache.commons.io.output.WriterOutputStream
+ * 
+ * @author <a href="mailto:veithen@apache.org">Andreas Veithen</a>
+ * @since Commons IO 2.0
+ */
+public class ReaderInputStream extends InputStream {
+    private static final int DEFAULT_BUFFER_SIZE = 1024;
+
+    private final Reader reader;
+    private final CharsetEncoder encoder;
+
+    /**
+     * CharBuffer used as input for the decoder. It should be reasonably
+     * large as we read data from the underlying Reader into this buffer.
+     */
+    private final CharBuffer encoderIn;
+
+    /**
+     * ByteBuffer used as output for the decoder. This buffer can be small
+     * as it is only used to transfer data from the decoder to the
+     * buffer provided by the caller.
+     */
+    private final ByteBuffer encoderOut = ByteBuffer.allocate(128);
+
+    private CoderResult lastCoderResult;
+    private boolean endOfInput;
+
+    /**
+     * Construct a new {@link ReaderInputStream}.
+     * 
+     * @param reader the target {@link Reader}
+     * @param charset the charset encoding
+     * @param bufferSize the size of the input buffer in number of characters
+     */
+    public ReaderInputStream(Reader reader, Charset charset, int bufferSize) {
+        this.reader = reader;
+        encoder = charset.newEncoder();
+        encoderIn = CharBuffer.allocate(bufferSize);
+        encoderIn.flip();
+    }
+
+    /**
+     * Construct a new {@link ReaderInputStream} with a default input buffer size of
+     * 1024 characters.
+     * 
+     * @param reader the target {@link Reader}
+     * @param charset the charset encoding
+     */
+    public ReaderInputStream(Reader reader, Charset charset) {
+        this(reader, charset, DEFAULT_BUFFER_SIZE);
+    }
+
+    /**
+     * Construct a new {@link ReaderInputStream}.
+     * 
+     * @param reader the target {@link Reader}
+     * @param charsetName the name of the charset encoding
+     * @param bufferSize the size of the input buffer in number of characters
+     */
+    public ReaderInputStream(Reader reader, String charsetName, int bufferSize) {
+        this(reader, Charset.forName(charsetName), bufferSize);
+    }
+
+    /**
+     * Construct a new {@link ReaderInputStream} with a default input buffer size of
+     * 1024 characters.
+     * 
+     * @param reader the target {@link Reader}
+     * @param charsetName the name of the charset encoding
+     */
+    public ReaderInputStream(Reader reader, String charsetName) {
+        this(reader, charsetName, DEFAULT_BUFFER_SIZE);
+    }
+
+    /**
+     * Construct a new {@link ReaderInputStream} that uses the default character encoding
+     * with a default input buffer size of 1024 characters.
+     * 
+     * @param reader the target {@link Reader}
+     */
+    public ReaderInputStream(Reader reader) {
+        this(reader, Charset.defaultCharset());
+    }
+
+    /**
+     * Read the specified number of bytes into an array.
+     * 
+     * @param b the byte array to read into
+     * @param off the offset to start reading bytes into
+     * @param len the number of bytes to read
+     * @return the number of bytes read or <code>-1</code>
+     *         if the end of the stream has been reached
+     * @throws IOException if an I/O error occurs
+     */
+    @Override
+    public int read(byte[] b, int off, int len) throws IOException {
+        int read = 0;
+        while (len > 0) {
+            if (encoderOut.position() > 0) {
+                encoderOut.flip();
+                int c = Math.min(encoderOut.remaining(), len);
+                encoderOut.get(b, off, c);
+                off += c;
+                len -= c;
+                read += c;
+                encoderOut.compact();
+            } else {
+                if (!endOfInput && (lastCoderResult == null || lastCoderResult.isUnderflow())) {
+                    encoderIn.compact();
+                    int position = encoderIn.position();
+                    // We don't use Reader#read(CharBuffer) here because it is more efficient
+                    // to write directly to the underlying char array (the default implementation
+                    // copies data to a temporary char array).
+                    int c = reader.read(encoderIn.array(), position, encoderIn.remaining());
+                    if (c == -1) {
+                        endOfInput = true;
+                    } else {
+                        encoderIn.position(position+c);
+                    }
+                    encoderIn.flip();
+                }
+                lastCoderResult = encoder.encode(encoderIn, encoderOut, endOfInput);
+                if (endOfInput && encoderOut.position() == 0) {
+                    break;
+                }
+            }
+        }
+        return read == 0 && endOfInput ? -1 : read;
+    }
+
+    /**
+     * Read the specified number of bytes into an array.
+     * 
+     * @param b the byte array to read into
+     * @return the number of bytes read or <code>-1</code>
+     *         if the end of the stream has been reached
+     * @throws IOException if an I/O error occurs
+     */
+    @Override
+    public int read(byte[] b) throws IOException {
+        return read(b, 0, b.length);
+    }
+
+    /**
+     * Read a single byte.
+     *
+     * @return either the byte read or <code>-1</code> if the end of the stream
+     *         has been reached
+     * @throws IOException if an I/O error occurs
+     */
+    @Override
+    public int read() throws IOException {
+        byte[] b = new byte[1];
+        return read(b) == -1 ? -1 : b[0] & 0xFF;
+    }
+
+    /**
+     * Close the stream. This method will cause the underlying {@link Reader}
+     * to be closed.
+     * @throws IOException if an I/O error occurs
+     */
+    @Override
+    public void close() throws IOException {
+        reader.close();
+    }
+}