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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;
18  
19  import java.io.FilterOutputStream;
20  import java.io.IOException;
21  import java.io.OutputStream;
22  
23  import org.apache.commons.io.IOUtils;
24  
25  /**
26   * A Proxy stream which acts as expected, that is it passes the method
27   * calls on to the proxied stream and doesn't change which methods are
28   * being called. It is an alternative base class to FilterOutputStream
29   * to increase reusability.
30   * <p>
31   * See the protected methods for ways in which a subclass can easily decorate
32   * a stream with custom pre-, post- or error processing functionality.
33   * </p>
34   */
35  public class ProxyOutputStream extends FilterOutputStream {
36  
37      /**
38       * Constructs a new ProxyOutputStream.
39       *
40       * @param proxy  the OutputStream to delegate to
41       */
42      public ProxyOutputStream(final OutputStream proxy) {
43          super(proxy);
44          // the proxy is stored in a protected superclass variable named 'out'
45      }
46  
47      /**
48       * Invoked by the write methods after the proxied call has returned
49       * successfully. The number of bytes written (1 for the
50       * {@link #write(int)} method, buffer length for {@link #write(byte[])},
51       * etc.) is given as an argument.
52       * <p>
53       * Subclasses can override this method to add common post-processing
54       * functionality without having to override all the write methods.
55       * The default implementation does nothing.
56       *
57       * @since 2.0
58       * @param n number of bytes written
59       * @throws IOException if the post-processing fails
60       */
61      @SuppressWarnings("unused") // Possibly thrown from subclasses.
62      protected void afterWrite(final int n) throws IOException {
63          // noop
64      }
65  
66      /**
67       * Invoked by the write methods before the call is proxied. The number
68       * of bytes to be written (1 for the {@link #write(int)} method, buffer
69       * length for {@link #write(byte[])}, etc.) is given as an argument.
70       * <p>
71       * Subclasses can override this method to add common pre-processing
72       * functionality without having to override all the write methods.
73       * The default implementation does nothing.
74       *
75       * @since 2.0
76       * @param n number of bytes to be written
77       * @throws IOException if the pre-processing fails
78       */
79      @SuppressWarnings("unused") // Possibly thrown from subclasses.
80      protected void beforeWrite(final int n) throws IOException {
81          // noop
82      }
83  
84      /**
85       * Invokes the delegate's {@code close()} method.
86       * @throws IOException if an I/O error occurs.
87       */
88      @Override
89      public void close() throws IOException {
90          IOUtils.close(out, this::handleIOException);
91      }
92  
93      /**
94       * Invokes the delegate's {@code flush()} method.
95       * @throws IOException if an I/O error occurs.
96       */
97      @Override
98      public void flush() throws IOException {
99          try {
100             out.flush();
101         } catch (final IOException e) {
102             handleIOException(e);
103         }
104     }
105 
106     /**
107      * Handle any IOExceptions thrown.
108      * <p>
109      * This method provides a point to implement custom exception
110      * handling. The default behavior is to re-throw the exception.
111      * @param e The IOException thrown
112      * @throws IOException if an I/O error occurs.
113      * @since 2.0
114      */
115     protected void handleIOException(final IOException e) throws IOException {
116         throw e;
117     }
118 
119     /**
120      * Invokes the delegate's {@code write(byte[])} method.
121      * @param bts the bytes to write
122      * @throws IOException if an I/O error occurs.
123      */
124     @Override
125     public void write(final byte[] bts) throws IOException {
126         try {
127             final int len = IOUtils.length(bts);
128             beforeWrite(len);
129             out.write(bts);
130             afterWrite(len);
131         } catch (final IOException e) {
132             handleIOException(e);
133         }
134     }
135 
136     /**
137      * Invokes the delegate's {@code write(byte[])} method.
138      * @param bts the bytes to write
139      * @param st The start offset
140      * @param end The number of bytes to write
141      * @throws IOException if an I/O error occurs.
142      */
143     @Override
144     public void write(final byte[] bts, final int st, final int end) throws IOException {
145         try {
146             beforeWrite(end);
147             out.write(bts, st, end);
148             afterWrite(end);
149         } catch (final IOException e) {
150             handleIOException(e);
151         }
152     }
153 
154     /**
155      * Invokes the delegate's {@code write(int)} method.
156      * @param idx the byte to write
157      * @throws IOException if an I/O error occurs.
158      */
159     @Override
160     public void write(final int idx) throws IOException {
161         try {
162             beforeWrite(1);
163             out.write(idx);
164             afterWrite(1);
165         } catch (final IOException e) {
166             handleIOException(e);
167         }
168     }
169 
170 }