    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.FilterWriter;
    020import java.io.IOException;
    021import java.io.Writer;
    022
    023import org.apache.commons.io.IOUtils;
    024
    025/**
    026 * A Proxy stream which acts as expected, that is it passes the method calls on to the proxied stream and doesn't
    027 * change which methods are being called. It is an alternative base class to FilterWriter to increase reusability,
    028 * because FilterWriter changes the methods being called, such as {@code write(char[]) to write(char[], int, int)}
    029 * and {@code write(String) to write(String, int, int)}.
    030 */
    031public class ProxyWriter extends FilterWriter {
    032
    033    /**
    034     * Constructs a new ProxyWriter.
    035     *
    036     * @param delegate  the Writer to delegate to
    037     */
    038    public ProxyWriter(final Writer delegate) {
    039        // the delegate is stored in a protected superclass variable named 'out'
    040        super(delegate);
    041    }
    042
    043    /**
    044     * Invoked by the write methods after the proxied call has returned
    045     * successfully. The number of chars written (1 for the
    046     * {@link #write(int)} method, buffer length for {@link #write(char[])},
    047     * etc.) is given as an argument.
    048     * <p>
    049     * Subclasses can override this method to add common post-processing
    050     * functionality without having to override all the write methods.
    051     * The default implementation does nothing.
    052     * </p>
    053     *
    054     * @param n number of chars written
    055     * @throws IOException if the post-processing fails
    056     * @since 2.0
    057     */
    058    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    059    protected void afterWrite(final int n) throws IOException {
    060        // noop
    061    }
    062
    063    /**
    064     * Invokes the delegate's {@code append(char)} method.
    065     * @param c The character to write
    066     * @return this writer
    067     * @throws IOException if an I/O error occurs.
    068     * @since 2.0
    069     */
    070    @Override
    071    public Writer append(final char c) throws IOException {
    072        try {
    073            beforeWrite(1);
    074            out.append(c);
    075            afterWrite(1);
    076        } catch (final IOException e) {
    077            handleIOException(e);
    078        }
    079        return this;
    080    }
    081
    082    /**
    083     * Invokes the delegate's {@code append(CharSequence)} method.
    084     * @param csq The character sequence to write
    085     * @return this writer
    086     * @throws IOException if an I/O error occurs.
    087     * @since 2.0
    088     */
    089    @Override
    090    public Writer append(final CharSequence csq) throws IOException {
    091        try {
    092            final int len = IOUtils.length(csq);
    093            beforeWrite(len);
    094            out.append(csq);
    095            afterWrite(len);
    096        } catch (final IOException e) {
    097            handleIOException(e);
    098        }
    099        return this;
    100    }
    101
    102    /**
    103     * Invokes the delegate's {@code append(CharSequence, int, int)} method.
    104     * @param csq The character sequence to write
    105     * @param start The index of the first character to write
    106     * @param end  The index of the first character to write (exclusive)
    107     * @return this writer
    108     * @throws IOException if an I/O error occurs.
    109     * @since 2.0
    110     */
    111    @Override
    112    public Writer append(final CharSequence csq, final int start, final int end) throws IOException {
    113        try {
    114            beforeWrite(end - start);
    115            out.append(csq, start, end);
    116            afterWrite(end - start);
    117        } catch (final IOException e) {
    118            handleIOException(e);
    119        }
    120        return this;
    121    }
    122
    123    /**
    124     * Invoked by the write methods before the call is proxied. The number
    125     * of chars to be written (1 for the {@link #write(int)} method, buffer
    126     * length for {@link #write(char[])}, etc.) is given as an argument.
    127     * <p>
    128     * Subclasses can override this method to add common pre-processing
    129     * functionality without having to override all the write methods.
    130     * The default implementation does nothing.
    131     * </p>
    132     *
    133     * @param n number of chars to be written
    134     * @throws IOException if the pre-processing fails
    135     * @since 2.0
    136     */
    137    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    138    protected void beforeWrite(final int n) throws IOException {
    139        // noop
    140    }
    141
    142    /**
    143     * Invokes the delegate's {@code close()} method.
    144     * @throws IOException if an I/O error occurs.
    145     */
    146    @Override
    147    public void close() throws IOException {
    148        IOUtils.close(out, this::handleIOException);
    149    }
    150
    151    /**
    152     * Invokes the delegate's {@code flush()} method.
    153     * @throws IOException if an I/O error occurs.
    154     */
    155    @Override
    156    public void flush() throws IOException {
    157        try {
    158            out.flush();
    159        } catch (final IOException e) {
    160            handleIOException(e);
    161        }
    162    }
    163
    164    /**
    165     * Handles any IOExceptions thrown.
    166     * <p>
    167     * This method provides a point to implement custom exception
    168     * handling. The default behavior is to re-throw the exception.
    169     * </p>
    170     *
    171     * @param e The IOException thrown
    172     * @throws IOException if an I/O error occurs.
    173     * @since 2.0
    174     */
    175    protected void handleIOException(final IOException e) throws IOException {
    176        throw e;
    177    }
    178
    179    /**
    180     * Invokes the delegate's {@code write(char[])} method.
    181     * @param cbuf the characters to write
    182     * @throws IOException if an I/O error occurs.
    183     */
    184    @Override
    185    public void write(final char[] cbuf) throws IOException {
    186        try {
    187            final int len = IOUtils.length(cbuf);
    188            beforeWrite(len);
    189            out.write(cbuf);
    190            afterWrite(len);
    191        } catch (final IOException e) {
    192            handleIOException(e);
    193        }
    194    }
    195
    196    /**
    197     * Invokes the delegate's {@code write(char[], int, int)} method.
    198     * @param cbuf the characters to write
    199     * @param off The start offset
    200     * @param len The number of characters to write
    201     * @throws IOException if an I/O error occurs.
    202     */
    203    @Override
    204    public void write(final char[] cbuf, final int off, final int len) throws IOException {
    205        try {
    206            beforeWrite(len);
    207            out.write(cbuf, off, len);
    208            afterWrite(len);
    209        } catch (final IOException e) {
    210            handleIOException(e);
    211        }
    212    }
    213
    214    /**
    215     * Invokes the delegate's {@code write(int)} method.
    216     * @param c the character to write
    217     * @throws IOException if an I/O error occurs.
    218     */
    219    @Override
    220    public void write(final int c) throws IOException {
    221        try {
    222            beforeWrite(1);
    223            out.write(c);
    224            afterWrite(1);
    225        } catch (final IOException e) {
    226            handleIOException(e);
    227        }
    228    }
    229
    230    /**
    231     * Invokes the delegate's {@code write(String)} method.
    232     * @param str the string to write
    233     * @throws IOException if an I/O error occurs.
    234     */
    235    @Override
    236    public void write(final String str) throws IOException {
    237        try {
    238            final int len = IOUtils.length(str);
    239            beforeWrite(len);
    240            out.write(str);
    241            afterWrite(len);
    242        } catch (final IOException e) {
    243            handleIOException(e);
    244        }
    245    }
    246
    247    /**
    248     * Invokes the delegate's {@code write(String)} method.
    249     * @param str the string to write
    250     * @param off The start offset
    251     * @param len The number of characters to write
    252     * @throws IOException if an I/O error occurs.
    253     */
    254    @Override
    255    public void write(final String str, final int off, final int len) throws IOException {
    256        try {
    257            beforeWrite(len);
    258            out.write(str, off, len);
    259            afterWrite(len);
    260        } catch (final IOException e) {
    261            handleIOException(e);
    262        }
    263    }
    264
    265}