    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.io.output;
    018
    019import java.io.IOException;
    020import java.io.OutputStream;
    021import java.io.Writer;
    022import java.nio.ByteBuffer;
    023import java.nio.CharBuffer;
    024import java.nio.charset.Charset;
    025import java.nio.charset.CharsetDecoder;
    026import java.nio.charset.CoderResult;
    027import java.nio.charset.CodingErrorAction;
    028
    029/**
    030 * {@link OutputStream} implementation that transforms a byte stream to a
    031 * character stream using a specified charset encoding and writes the resulting
    032 * stream to a {@link Writer}. The stream is transformed using a
    033 * {@link CharsetDecoder} object, guaranteeing that all charset
    034 * encodings supported by the JRE are handled correctly.
    035 * <p>
    036 * The output of the {@link CharsetDecoder} is buffered using a fixed size buffer.
    037 * This implies that the data is written to the underlying {@link Writer} in chunks
    038 * that are no larger than the size of this buffer. By default, the buffer is
    039 * flushed only when it overflows or when {@link #flush()} or {@link #close()}
    040 * is called. In general there is therefore no need to wrap the underlying {@link Writer}
    041 * in a {@link java.io.BufferedWriter}. {@link WriterOutputStream} can also
    042 * be instructed to flush the buffer after each write operation. In this case, all
    043 * available data is written immediately to the underlying {@link Writer}, implying that
    044 * the current position of the {@link Writer} is correlated to the current position
    045 * of the {@link WriterOutputStream}.
    046 * <p>
    047 * {@link WriterOutputStream} implements the inverse transformation of {@link java.io.OutputStreamWriter};
    048 * in the following example, writing to {@code out2} would have the same result as writing to
    049 * {@code out} directly (provided that the byte sequence is legal with respect to the
    050 * charset encoding):
    051 * <pre>
    052 * OutputStream out = ...
    053 * Charset cs = ...
    054 * OutputStreamWriter writer = new OutputStreamWriter(out, cs);
    055 * WriterOutputStream out2 = new WriterOutputStream(writer, cs);</pre>
    056 * {@link WriterOutputStream} implements the same transformation as {@link java.io.InputStreamReader},
    057 * except that the control flow is reversed: both classes transform a byte stream
    058 * into a character stream, but {@link java.io.InputStreamReader} pulls data from the underlying stream,
    059 * while {@link WriterOutputStream} pushes it to the underlying stream.
    060 * <p>
    061 * Note that while there are use cases where there is no alternative to using
    062 * this class, very often the need to use this class is an indication of a flaw
    063 * in the design of the code. This class is typically used in situations where an existing
    064 * API only accepts an {@link OutputStream} object, but where the stream is known to represent
    065 * character data that must be decoded for further use.
    066 * <p>
    067 * Instances of {@link WriterOutputStream} are not thread safe.
    068 *
    069 * @see org.apache.commons.io.input.ReaderInputStream
    070 *
    071 * @since 2.0
    072 */
    073public class WriterOutputStream extends OutputStream {
    074    private static final int BUFFER_SIZE = 1024;
    075
    076    private final Writer writer;
    077    private final CharsetDecoder decoder;
    078    private final boolean writeImmediately;
    079
    080    /**
    081     * ByteBuffer used as input for the decoder. This buffer can be small
    082     * as it is used only to transfer the received data to the
    083     * decoder.
    084     */
    085    private final ByteBuffer decoderIn = ByteBuffer.allocate(128);
    086
    087    /**
    088     * CharBuffer used as output for the decoder. It should be
    089     * somewhat larger as we write from this buffer to the
    090     * underlying Writer.
    091     */
    092    private final CharBuffer decoderOut;
    093
    094    /**
    095     * Constructs a new {@link WriterOutputStream} with a default output buffer size of {@value #BUFFER_SIZE}
    096     * characters. The output buffer will only be flushed when it overflows or when {@link #flush()} or {@link #close()}
    097     * is called.
    098     *
    099     * @param writer the target {@link Writer}
    100     * @param decoder the charset decoder
    101     * @since 2.1
    102     */
    103    public WriterOutputStream(final Writer writer, final CharsetDecoder decoder) {
    104        this(writer, decoder, BUFFER_SIZE, false);
    105    }
    106
    107    /**
    108     * Constructs a new {@link WriterOutputStream}.
    109     *
    110     * @param writer the target {@link Writer}
    111     * @param decoder the charset decoder
    112     * @param bufferSize the size of the output buffer in number of characters
    113     * @param writeImmediately If {@code true} the output buffer will be flushed after each
    114     *                         write operation, i.e. all available data will be written to the
    115     *                         underlying {@link Writer} immediately. If {@code false}, the
    116     *                         output buffer will only be flushed when it overflows or when
    117     *                         {@link #flush()} or {@link #close()} is called.
    118     * @since 2.1
    119     */
    120    public WriterOutputStream(final Writer writer, final CharsetDecoder decoder, final int bufferSize,
    121                              final boolean writeImmediately) {
    122        checkIbmJdkWithBrokenUTF16( decoder.charset());
    123        this.writer = writer;
    124        this.decoder = decoder;
    125        this.writeImmediately = writeImmediately;
    126        decoderOut = CharBuffer.allocate(bufferSize);
    127    }
    128
    129    /**
    130     * Constructs a new {@link WriterOutputStream}.
    131     *
    132     * @param writer the target {@link Writer}
    133     * @param charset the charset encoding
    134     * @param bufferSize the size of the output buffer in number of characters
    135     * @param writeImmediately If {@code true} the output buffer will be flushed after each
    136     *                         write operation, i.e. all available data will be written to the
    137     *                         underlying {@link Writer} immediately. If {@code false}, the
    138     *                         output buffer will only be flushed when it overflows or when
    139     *                         {@link #flush()} or {@link #close()} is called.
    140     */
    141    public WriterOutputStream(final Writer writer, final Charset charset, final int bufferSize,
    142                              final boolean writeImmediately) {
    143        this(writer,
    144             charset.newDecoder()
    145                    .onMalformedInput(CodingErrorAction.REPLACE)
    146                    .onUnmappableCharacter(CodingErrorAction.REPLACE)
    147                    .replaceWith("?"),
    148             bufferSize,
    149             writeImmediately);
    150    }
    151
    152    /**
    153     * Constructs a new {@link WriterOutputStream} with a default output buffer size of {@value #BUFFER_SIZE}
    154     * characters. The output buffer will only be flushed when it overflows or when {@link #flush()} or {@link #close()}
    155     * is called.
    156     *
    157     * @param writer the target {@link Writer}
    158     * @param charset the charset encoding
    159     */
    160    public WriterOutputStream(final Writer writer, final Charset charset) {
    161        this(writer, charset, BUFFER_SIZE, false);
    162    }
    163
    164    /**
    165     * Constructs a new {@link WriterOutputStream}.
    166     *
    167     * @param writer the target {@link Writer}
    168     * @param charsetName the name of the charset encoding
    169     * @param bufferSize the size of the output buffer in number of characters
    170     * @param writeImmediately If {@code true} the output buffer will be flushed after each
    171     *                         write operation, i.e. all available data will be written to the
    172     *                         underlying {@link Writer} immediately. If {@code false}, the
    173     *                         output buffer will only be flushed when it overflows or when
    174     *                         {@link #flush()} or {@link #close()} is called.
    175     */
    176    public WriterOutputStream(final Writer writer, final String charsetName, final int bufferSize,
    177                              final boolean writeImmediately) {
    178        this(writer, Charset.forName(charsetName), bufferSize, writeImmediately);
    179    }
    180
    181    /**
    182     * Constructs a new {@link WriterOutputStream} with a default output buffer size of {@value #BUFFER_SIZE}
    183     * characters. The output buffer will only be flushed when it overflows or when {@link #flush()} or {@link #close()}
    184     * is called.
    185     *
    186     * @param writer the target {@link Writer}
    187     * @param charsetName the name of the charset encoding
    188     */
    189    public WriterOutputStream(final Writer writer, final String charsetName) {
    190        this(writer, charsetName, BUFFER_SIZE, false);
    191    }
    192
    193    /**
    194     * Constructs a new {@link WriterOutputStream} that uses the default character encoding and with a default output
    195     * buffer size of {@value #BUFFER_SIZE} characters. The output buffer will only be flushed when it overflows or when
    196     * {@link #flush()} or {@link #close()} is called.
    197     *
    198     * @param writer the target {@link Writer}
    199     * @deprecated 2.5 use {@link #WriterOutputStream(Writer, Charset)} instead
    200     */
    201    @Deprecated
    202    public WriterOutputStream(final Writer writer) {
    203        this(writer, Charset.defaultCharset(), BUFFER_SIZE, false);
    204    }
    205
    206    /**
    207     * Write bytes from the specified byte array to the stream.
    208     *
    209     * @param b the byte array containing the bytes to write
    210     * @param off the start offset in the byte array
    211     * @param len the number of bytes to write
    212     * @throws IOException if an I/O error occurs
    213     */
    214    @Override
    215    public void write(final byte[] b, int off, int len) throws IOException {
    216        while (len > 0) {
    217            final int c = Math.min(len, decoderIn.remaining());
    218            decoderIn.put(b, off, c);
    219            processInput(false);
    220            len -= c;
    221            off += c;
    222        }
    223        if (writeImmediately) {
    224            flushOutput();
    225        }
    226    }
    227
    228    /**
    229     * Write bytes from the specified byte array to the stream.
    230     *
    231     * @param b the byte array containing the bytes to write
    232     * @throws IOException if an I/O error occurs
    233     */
    234    @Override
    235    public void write(final byte[] b) throws IOException {
    236        write(b, 0, b.length);
    237    }
    238
    239    /**
    240     * Write a single byte to the stream.
    241     *
    242     * @param b the byte to write
    243     * @throws IOException if an I/O error occurs
    244     */
    245    @Override
    246    public void write(final int b) throws IOException {
    247        write(new byte[] { (byte)b }, 0, 1);
    248    }
    249
    250    /**
    251     * Flush the stream. Any remaining content accumulated in the output buffer
    252     * will be written to the underlying {@link Writer}. After that
    253     * {@link Writer#flush()} will be called.
    254     * @throws IOException if an I/O error occurs
    255     */
    256    @Override
    257    public void flush() throws IOException {
    258        flushOutput();
    259        writer.flush();
    260    }
    261
    262    /**
    263     * Close the stream. Any remaining content accumulated in the output buffer
    264     * will be written to the underlying {@link Writer}. After that
    265     * {@link Writer#close()} will be called.
    266     * @throws IOException if an I/O error occurs
    267     */
    268    @Override
    269    public void close() throws IOException {
    270        processInput(true);
    271        flushOutput();
    272        writer.close();
    273    }
    274
    275    /**
    276     * Decode the contents of the input ByteBuffer into a CharBuffer.
    277     *
    278     * @param endOfInput indicates end of input
    279     * @throws IOException if an I/O error occurs
    280     */
    281    private void processInput(final boolean endOfInput) throws IOException {
    282        // Prepare decoderIn for reading
    283        decoderIn.flip();
    284        CoderResult coderResult;
    285        while (true) {
    286            coderResult = decoder.decode(decoderIn, decoderOut, endOfInput);
    287            if (coderResult.isOverflow()) {
    288                flushOutput();
    289            } else if (coderResult.isUnderflow()) {
    290                break;
    291            } else {
    292                // The decoder is configured to replace malformed input and unmappable characters,
    293                // so we should not get here.
    294                throw new IOException("Unexpected coder result");
    295            }
    296        }
    297        // Discard the bytes that have been read
    298        decoderIn.compact();
    299    }
    300
    301    /**
    302     * Flush the output.
    303     *
    304     * @throws IOException if an I/O error occurs
    305     */
    306    private void flushOutput() throws IOException {
    307        if (decoderOut.position() > 0) {
    308            writer.write(decoderOut.array(), 0, decoderOut.position());
    309            decoderOut.rewind();
    310        }
    311    }
    312
    313    /**
    314     * Check if the JDK in use properly supports the given charset.
    315     *
    316     * @param charset the charset to check the support for
    317     */
    318    private static void checkIbmJdkWithBrokenUTF16(final Charset charset){
    319        if (!"UTF-16".equals(charset.name())) {
    320            return;
    321        }
    322        final String TEST_STRING_2 = "v\u00e9s";
    323        final byte[] bytes = TEST_STRING_2.getBytes(charset);
    324
    325        final CharsetDecoder charsetDecoder2 = charset.newDecoder();
    326        final ByteBuffer bb2 = ByteBuffer.allocate(16);
    327        final CharBuffer cb2 = CharBuffer.allocate(TEST_STRING_2.length());
    328        final int len = bytes.length;
    329        for (int i = 0; i < len; i++) {
    330            bb2.put(bytes[i]);
    331            bb2.flip();
    332            try {
    333                charsetDecoder2.decode(bb2, cb2, i == (len - 1));
    334            } catch ( final IllegalArgumentException e){
    335                throw new UnsupportedOperationException("UTF-16 requested when runninng on an IBM JDK with broken UTF-16 support. " +
    336                        "Please find a JDK that supports UTF-16 if you intend to use UF-16 with WriterOutputStream");
    337            }
    338            bb2.compact();
    339        }
    340        cb2.rewind();
    341        if (!TEST_STRING_2.equals(cb2.toString())){
    342            throw new UnsupportedOperationException("UTF-16 requested when runninng on an IBM JDK with broken UTF-16 support. " +
    343                    "Please find a JDK that supports UTF-16 if you intend to use UF-16 with WriterOutputStream");
    344        }
    345
    346    }
    347}