    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.FilterOutputStream;
    020import java.io.IOException;
    021import java.io.OutputStream;
    022
    023import org.apache.commons.io.IOUtils;
    024import org.apache.commons.io.build.AbstractStreamBuilder;
    025
    026/**
    027 * A Proxy stream which acts as expected, that is it passes the method
    028 * calls on to the proxied stream and doesn't change which methods are
    029 * being called. It is an alternative base class to FilterOutputStream
    030 * to increase reusability.
    031 * <p>
    032 * See the protected methods for ways in which a subclass can easily decorate
    033 * a stream with custom pre-, post- or error processing functionality.
    034 * </p>
    035 */
    036public class ProxyOutputStream extends FilterOutputStream {
    037
    038    /**
    039     * Builds instances of {@link ProxyOutputStream}.
    040     * <p>
    041     * This class does not provide a convenience static {@code builder()} method so that subclasses can.
    042     * </p>
    043     *
    044     * @since 2.19.0
    045     */
    046    public static class Builder extends AbstractStreamBuilder<ProxyOutputStream, Builder> {
    047
    048        /**
    049         * Constructs a new builder of {@link ProxyOutputStream}.
    050         */
    051        public Builder() {
    052            // empty
    053        }
    054
    055        /**
    056         * Builds a new {@link ProxyOutputStream}.
    057         * <p>
    058         * This builder uses the following aspects:
    059         * </p>
    060         * <ul>
    061         * <li>{@link #getOutputStream()} is the target aspect.</li>
    062         * </ul>
    063         *
    064         * @return a new instance.
    065         * @throws IllegalStateException         if the {@code origin} is {@code null}.
    066         * @throws UnsupportedOperationException if the origin cannot be converted to an {@link OutputStream}.
    067         * @throws IOException                   if an I/O error occurs converting to an {@link OutputStream} using {@link #getOutputStream()}.
    068         * @see #getOutputStream()
    069         * @see #getUnchecked()
    070         */
    071        @SuppressWarnings("resource") // caller closes
    072        @Override
    073        public ProxyOutputStream get() throws IOException {
    074            return new ProxyOutputStream(getOutputStream());
    075        }
    076
    077    }
    078
    079    /**
    080     * Constructs a new ProxyOutputStream.
    081     *
    082     * @param delegate  the OutputStream to delegate to
    083     */
    084    public ProxyOutputStream(final OutputStream delegate) {
    085        // the delegate is stored in a protected superclass variable named 'out'
    086        super(delegate);
    087    }
    088
    089    /**
    090     * Invoked by the write methods after the proxied call has returned
    091     * successfully. The number of bytes written (1 for the
    092     * {@link #write(int)} method, buffer length for {@link #write(byte[])},
    093     * etc.) is given as an argument.
    094     * <p>
    095     * Subclasses can override this method to add common post-processing
    096     * functionality without having to override all the write methods.
    097     * The default implementation does nothing.
    098     *
    099     * @param n number of bytes written
    100     * @throws IOException if the post-processing fails
    101     * @since 2.0
    102     */
    103    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    104    protected void afterWrite(final int n) throws IOException {
    105        // noop
    106    }
    107
    108    /**
    109     * Invoked by the write methods before the call is proxied. The number
    110     * of bytes to be written (1 for the {@link #write(int)} method, buffer
    111     * length for {@link #write(byte[])}, etc.) is given as an argument.
    112     * <p>
    113     * Subclasses can override this method to add common pre-processing
    114     * functionality without having to override all the write methods.
    115     * The default implementation does nothing.
    116     *
    117     * @param n number of bytes to be written
    118     * @throws IOException if the pre-processing fails
    119     * @since 2.0
    120     */
    121    @SuppressWarnings("unused") // Possibly thrown from subclasses.
    122    protected void beforeWrite(final int n) throws IOException {
    123        // noop
    124    }
    125
    126    /**
    127     * Invokes the delegate's {@code close()} method.
    128     * @throws IOException if an I/O error occurs.
    129     */
    130    @Override
    131    public void close() throws IOException {
    132        IOUtils.close(out, this::handleIOException);
    133    }
    134
    135    /**
    136     * Invokes the delegate's {@code flush()} method.
    137     * @throws IOException if an I/O error occurs.
    138     */
    139    @Override
    140    public void flush() throws IOException {
    141        try {
    142            out.flush();
    143        } catch (final IOException e) {
    144            handleIOException(e);
    145        }
    146    }
    147
    148    /**
    149     * Handle any IOExceptions thrown.
    150     * <p>
    151     * This method provides a point to implement custom exception
    152     * handling. The default behavior is to re-throw the exception.
    153     * @param e The IOException thrown
    154     * @throws IOException if an I/O error occurs.
    155     * @since 2.0
    156     */
    157    protected void handleIOException(final IOException e) throws IOException {
    158        throw e;
    159    }
    160
    161    /**
    162     * Sets the underlying output stream.
    163     *
    164     * @param out the underlying output stream.
    165     * @return this instance.
    166     * @since 2.19.0
    167     */
    168    public ProxyOutputStream setReference(final OutputStream out) {
    169        this.out = out;
    170        return this;
    171    }
    172
    173    /**
    174     * Unwraps this instance by returning the underlying {@link OutputStream}.
    175     * <p>
    176     * Use with caution; useful to query the underlying {@link OutputStream}.
    177     * </p>
    178     *
    179     * @return the underlying {@link OutputStream}.
    180     */
    181    OutputStream unwrap() {
    182        return out;
    183    }
    184
    185    /**
    186     * Invokes the delegate's {@code write(byte[])} method.
    187     * @param bts the bytes to write
    188     * @throws IOException if an I/O error occurs.
    189     */
    190    @Override
    191    public void write(final byte[] bts) throws IOException {
    192        try {
    193            final int len = IOUtils.length(bts);
    194            beforeWrite(len);
    195            out.write(bts);
    196            afterWrite(len);
    197        } catch (final IOException e) {
    198            handleIOException(e);
    199        }
    200    }
    201
    202    /**
    203     * Invokes the delegate's {@code write(byte[])} method.
    204     * @param bts the bytes to write
    205     * @param st The start offset
    206     * @param end The number of bytes to write
    207     * @throws IOException if an I/O error occurs.
    208     */
    209    @Override
    210    public void write(final byte[] bts, final int st, final int end) throws IOException {
    211        try {
    212            beforeWrite(end);
    213            out.write(bts, st, end);
    214            afterWrite(end);
    215        } catch (final IOException e) {
    216            handleIOException(e);
    217        }
    218    }
    219
    220    /**
    221     * Invokes the delegate's {@code write(int)} method.
    222     * @param idx the byte to write
    223     * @throws IOException if an I/O error occurs.
    224     */
    225    @Override
    226    public void write(final int idx) throws IOException {
    227        try {
    228            beforeWrite(1);
    229            out.write(idx);
    230            afterWrite(1);
    231        } catch (final IOException e) {
    232            handleIOException(e);
    233        }
    234    }
    235
    236}