/*
* 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.output;
import java.io.IOException;
import java.io.OutputStream;
import java.io.Writer;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CoderResult;
import java.nio.charset.CodingErrorAction;
/**
* {@link OutputStream} implementation that transforms a byte stream to a
* character stream using a specified charset encoding and writes the resulting
* stream to a {@link Writer}. The stream is transformed using a
* {@link CharsetDecoder} object, guaranteeing that all charset
* encodings supported by the JRE are handled correctly.
* <p>
* The output of the {@link CharsetDecoder} is buffered using a fixed size buffer.
* This implies that the data is written to the underlying {@link Writer} in chunks
* that are no larger than the size of this buffer. By default, the buffer is
* flushed only when it overflows or when {@link #flush()} or {@link #close()}
* is called. In general there is therefore no need to wrap the underlying {@link Writer}
* in a {@link java.io.BufferedWriter}. {@link WriterOutputStream} can also
* be instructed to flush the buffer after each write operation. In this case, all
* available data is written immediately to the underlying {@link Writer}, implying that
* the current position of the {@link Writer} is correlated to the current position
* of the {@link WriterOutputStream}.
* <p>
* {@link WriterOutputStream} implements the inverse transformation of {@link java.io.OutputStreamWriter};
* in the following example, writing to <tt>out2</tt> would have the same result as writing to
* <tt>out</tt> directly (provided that the byte sequence is legal with respect to the
* charset encoding):
* <pre>
* OutputStream out = ...
* Charset cs = ...
* OutputStreamWriter writer = new OutputStreamWriter(out, cs);
* WriterOutputStream out2 = new WriterOutputStream(writer, cs);</pre>
* {@link WriterOutputStream} implements the same transformation as {@link java.io.InputStreamReader},
* except that the control flow is reversed: both classes transform a byte stream
* into a character stream, but {@link java.io.InputStreamReader} pulls data from the underlying stream,
* while {@link WriterOutputStream} pushes it to 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 OutputStream} object, but where the stream is known to represent
* character data that must be decoded for further use.
* <p>
* Instances of {@link WriterOutputStream} are not thread safe.
*
* @see org.apache.commons.io.input.ReaderInputStream
*
* @since 2.0
*/
public class WriterOutputStream extends OutputStream {
private static final int DEFAULT_BUFFER_SIZE = 1024;
private final Writer writer;
private final CharsetDecoder decoder;
private final boolean writeImmediately;
/**
* ByteBuffer used as input for the decoder. This buffer can be small
* as it is used only to transfer the received data to the
* decoder.
*/
private final ByteBuffer decoderIn = ByteBuffer.allocate(128);
/**
* CharBuffer used as output for the decoder. It should be
* somewhat larger as we write from this buffer to the
* underlying Writer.
*/
private final CharBuffer decoderOut;
/**
* Constructs a new {@link WriterOutputStream} with a default output buffer size of
* 1024 characters. The output buffer will only be flushed when it overflows or when
* {@link #flush()} or {@link #close()} is called.
*
* @param writer the target {@link Writer}
* @param decoder the charset decoder
* @since 2.1
*/
public WriterOutputStream(Writer writer, CharsetDecoder decoder) {
this(writer, decoder, DEFAULT_BUFFER_SIZE, false);
}
/**
* Constructs a new {@link WriterOutputStream}.
*
* @param writer the target {@link Writer}
* @param decoder the charset decoder
* @param bufferSize the size of the output buffer in number of characters
* @param writeImmediately If <tt>true</tt> the output buffer will be flushed after each
* write operation, i.e. all available data will be written to the
* underlying {@link Writer} immediately. If <tt>false</tt>, the
* output buffer will only be flushed when it overflows or when
* {@link #flush()} or {@link #close()} is called.
* @since 2.1
*/
public WriterOutputStream(Writer writer, CharsetDecoder decoder, int bufferSize, boolean writeImmediately) {
this.writer = writer;
this.decoder = decoder;
this.writeImmediately = writeImmediately;
decoderOut = CharBuffer.allocate(bufferSize);
}
/**
* Constructs a new {@link WriterOutputStream}.
*
* @param writer the target {@link Writer}
* @param charset the charset encoding
* @param bufferSize the size of the output buffer in number of characters
* @param writeImmediately If <tt>true</tt> the output buffer will be flushed after each
* write operation, i.e. all available data will be written to the
* underlying {@link Writer} immediately. If <tt>false</tt>, the
* output buffer will only be flushed when it overflows or when
* {@link #flush()} or {@link #close()} is called.
*/
public WriterOutputStream(Writer writer, Charset charset, int bufferSize, boolean writeImmediately) {
this(writer,
charset.newDecoder()
.onMalformedInput(CodingErrorAction.REPLACE)
.onUnmappableCharacter(CodingErrorAction.REPLACE)
.replaceWith("?"),
bufferSize,
writeImmediately);
}
/**
* Constructs a new {@link WriterOutputStream} with a default output buffer size of
* 1024 characters. The output buffer will only be flushed when it overflows or when
* {@link #flush()} or {@link #close()} is called.
*
* @param writer the target {@link Writer}
* @param charset the charset encoding
*/
public WriterOutputStream(Writer writer, Charset charset) {
this(writer, charset, DEFAULT_BUFFER_SIZE, false);
}
/**
* Constructs a new {@link WriterOutputStream}.
*
* @param writer the target {@link Writer}
* @param charsetName the name of the charset encoding
* @param bufferSize the size of the output buffer in number of characters
* @param writeImmediately If <tt>true</tt> the output buffer will be flushed after each
* write operation, i.e. all available data will be written to the
* underlying {@link Writer} immediately. If <tt>false</tt>, the
* output buffer will only be flushed when it overflows or when
* {@link #flush()} or {@link #close()} is called.
*/
public WriterOutputStream(Writer writer, String charsetName, int bufferSize, boolean writeImmediately) {
this(writer, Charset.forName(charsetName), bufferSize, writeImmediately);
}
/**
* Constructs a new {@link WriterOutputStream} with a default output buffer size of
* 1024 characters. The output buffer will only be flushed when it overflows or when
* {@link #flush()} or {@link #close()} is called.
*
* @param writer the target {@link Writer}
* @param charsetName the name of the charset encoding
*/
public WriterOutputStream(Writer writer, String charsetName) {
this(writer, charsetName, DEFAULT_BUFFER_SIZE, false);
}
/**
* Constructs a new {@link WriterOutputStream} that uses the default character encoding
* and with a default output buffer size of 1024 characters. The output buffer will only
* be flushed when it overflows or when {@link #flush()} or {@link #close()} is called.
*
* @param writer the target {@link Writer}
*/
public WriterOutputStream(Writer writer) {
this(writer, Charset.defaultCharset(), DEFAULT_BUFFER_SIZE, false);
}
/**
* Write bytes from the specified byte array to the stream.
*
* @param b the byte array containing the bytes to write
* @param off the start offset in the byte array
* @param len the number of bytes to write
* @throws IOException if an I/O error occurs
*/
@Override
public void write(byte[] b, int off, int len) throws IOException {
while (len > 0) {
int c = Math.min(len, decoderIn.remaining());
decoderIn.put(b, off, c);
processInput(false);
len -= c;
off += c;
}
if (writeImmediately) {
flushOutput();
}
}
/**
* Write bytes from the specified byte array to the stream.
*
* @param b the byte array containing the bytes to write
* @throws IOException if an I/O error occurs
*/
@Override
public void write(byte[] b) throws IOException {
write(b, 0, b.length);
}
/**
* Write a single byte to the stream.
*
* @param b the byte to write
* @throws IOException if an I/O error occurs
*/
@Override
public void write(int b) throws IOException {
write(new byte[] { (byte)b }, 0, 1);
}
/**
* Flush the stream. Any remaining content accumulated in the output buffer
* will be written to the underlying {@link Writer}. After that
* {@link Writer#flush()} will be called.
* @throws IOException if an I/O error occurs
*/
@Override
public void flush() throws IOException {
flushOutput();
writer.flush();
}
/**
* Close the stream. Any remaining content accumulated in the output buffer
* will be written to the underlying {@link Writer}. After that
* {@link Writer#close()} will be called.
* @throws IOException if an I/O error occurs
*/
@Override
public void close() throws IOException {
processInput(true);
flushOutput();
writer.close();
}
/**
* Decode the contents of the input ByteBuffer into a CharBuffer.
*
* @param endOfInput indicates end of input
* @throws IOException if an I/O error occurs
*/
private void processInput(boolean endOfInput) throws IOException {
// Prepare decoderIn for reading
decoderIn.flip();
CoderResult coderResult;
while (true) {
coderResult = decoder.decode(decoderIn, decoderOut, endOfInput);
if (coderResult.isOverflow()) {
flushOutput();
} else if (coderResult.isUnderflow()) {
break;
} else {
// The decoder is configured to replace malformed input and unmappable characters,
// so we should not get here.
throw new IOException("Unexpected coder result");
}
}
// Discard the bytes that have been read
decoderIn.compact();
}
/**
* Flush the output.
*
* @throws IOException if an I/O error occurs
*/
private void flushOutput() throws IOException {
if (decoderOut.position() > 0) {
writer.write(decoderOut.array(), 0, decoderOut.position());
decoderOut.rewind();
}
}
}