com.github.lespaul361.commons.commonroutines.utilities.Streams.WriterOutputStream Maven / Gradle / Ivy
/*
* 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 com.github.lespaul361.commons.commonroutines.utilities.Streams;
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.
*
* 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}.
*
* {@link WriterOutputStream} implements the inverse transformation of
* {@link java.io.OutputStreamWriter}; in the following example, writing to
* out2 would have the same result as writing to
* out directly (provided that the byte sequence is legal with respect
* to the charset encoding):
*
* OutputStream out = ...
* Charset cs = ...
* OutputStreamWriter writer = new OutputStreamWriter(out, cs);
* WriterOutputStream out2 = new WriterOutputStream(writer, cs);
* {@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.
*
* 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.
*
* Instances of {@link WriterOutputStream} are not thread safe.
*
* @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(final Writer writer, final 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 true 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 false,
* the output buffer will only be flushed when it overflows or when
* {@link #flush()} or {@link #close()} is called.
* @since 2.1
*/
public WriterOutputStream(final Writer writer, final CharsetDecoder decoder, final int bufferSize, final 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 true 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 false,
* the output buffer will only be flushed when it overflows or when
* {@link #flush()} or {@link #close()} is called.
*/
public WriterOutputStream(final Writer writer, final Charset charset, final int bufferSize, final 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(final Writer writer, final 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 true 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 false,
* the output buffer will only be flushed when it overflows or when
* {@link #flush()} or {@link #close()} is called.
*/
public WriterOutputStream(final Writer writer, final String charsetName, final int bufferSize, final 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(final Writer writer, final 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}
* @deprecated 2.5 use {@link #WriterOutputStream(Writer, Charset)} instead
*/
@Deprecated
public WriterOutputStream(final 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(final byte[] b, int off, int len) throws IOException {
while (len > 0) {
final 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(final 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(final 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(final 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();
}
}
}