ProxyOutputStream.java

  1. /*
  2.  * Licensed to the Apache Software Foundation (ASF) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * The ASF licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *      http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.apache.commons.io.output;

  19. import java.io.FilterOutputStream;
  20. import java.io.IOException;
  21. import java.io.OutputStream;

  23. import org.apache.commons.io.IOUtils;
  24. import org.apache.commons.io.build.AbstractStreamBuilder;

  26. /**
  27.  * A Proxy stream which acts as expected, that is it passes the method
  28.  * calls on to the proxied stream and doesn't change which methods are
  29.  * being called. It is an alternative base class to FilterOutputStream
  30.  * to increase reusability.
  31.  * <p>
  32.  * See the protected methods for ways in which a subclass can easily decorate
  33.  * a stream with custom pre-, post- or error processing functionality.
  34.  * </p>
  35.  */
  36. public class ProxyOutputStream extends FilterOutputStream {

  38.     /**
  39.      * Builds instances of {@link ProxyOutputStream}.
  40.      * <p>
  41.      * This class does not provide a convenience static {@code builder()} method so that subclasses can.
  42.      * </p>
  43.      *
  44.      * @since 2.19.0
  45.      */
  46.     public static class Builder extends AbstractStreamBuilder<ProxyOutputStream, Builder> {

  48.         /**
  49.          * Constructs a new builder of {@link ProxyOutputStream}.
  50.          */
  51.         public Builder() {
  52.             // empty
  53.         }

  55.         /**
  56.          * Builds a new {@link ProxyOutputStream}.
  57.          * <p>
  58.          * This builder uses the following aspects:
  59.          * </p>
  60.          * <ul>
  61.          * <li>{@link #getOutputStream()} is the target aspect.</li>
  62.          * </ul>
  63.          *
  64.          * @return a new instance.
  65.          * @throws IllegalStateException         if the {@code origin} is {@code null}.
  66.          * @throws UnsupportedOperationException if the origin cannot be converted to an {@link OutputStream}.
  67.          * @throws IOException                   if an I/O error occurs converting to an {@link OutputStream} using {@link #getOutputStream()}.
  68.          * @see #getOutputStream()
  69.          * @see #getUnchecked()
  70.          */
  71.         @SuppressWarnings("resource") // caller closes
  72.         @Override
  73.         public ProxyOutputStream get() throws IOException {
  74.             return new ProxyOutputStream(getOutputStream());
  75.         }

  77.     }

  79.     /**
  80.      * Constructs a new ProxyOutputStream.
  81.      *
  82.      * @param delegate  the OutputStream to delegate to
  83.      */
  84.     public ProxyOutputStream(final OutputStream delegate) {
  85.         // the delegate is stored in a protected superclass variable named 'out'
  86.         super(delegate);
  87.     }

  89.     /**
  90.      * Invoked by the write methods after the proxied call has returned
  91.      * successfully. The number of bytes written (1 for the
  92.      * {@link #write(int)} method, buffer length for {@link #write(byte[])},
  93.      * etc.) is given as an argument.
  94.      * <p>
  95.      * Subclasses can override this method to add common post-processing
  96.      * functionality without having to override all the write methods.
  97.      * The default implementation does nothing.
  98.      *
  99.      * @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.     }

  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.     }

  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.     }

  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.     }

  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.     }

  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.     }

  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.     }

  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.     }

  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.     }

  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.     }

  236. }
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