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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.IOException;
20  import java.io.OutputStream;
21  
22  import org.apache.commons.io.IOUtils;
23  
24  /**
25   * Forwards data to a stream that has been associated with this thread.
26   */
27  public class DemuxOutputStream extends OutputStream {
28  
29      private final InheritableThreadLocal<OutputStream> outputStreamThreadLocal = new InheritableThreadLocal<>();
30  
31      /**
32       * Construct a new instance.
33       */
34      public DemuxOutputStream() {
35          // empty
36      }
37  
38      /**
39       * Binds the specified stream to the current thread.
40       *
41       * @param output
42       *            the stream to bind
43       * @return the OutputStream that was previously active
44       */
45      public OutputStream bindStream(final OutputStream output) {
46          final OutputStream stream = outputStreamThreadLocal.get();
47          outputStreamThreadLocal.set(output);
48          return stream;
49      }
50  
51      /**
52       * Closes stream associated with current thread.
53       *
54       * @throws IOException
55       *             if an error occurs
56       */
57      @SuppressWarnings("resource") // we actually close the stream here
58      @Override
59      public void close() throws IOException {
60          IOUtils.close(outputStreamThreadLocal.get());
61      }
62  
63      /**
64       * Flushes stream associated with current thread.
65       *
66       * @throws IOException
67       *             if an error occurs
68       */
69      @Override
70      public void flush() throws IOException {
71          @SuppressWarnings("resource")
72          final OutputStream output = outputStreamThreadLocal.get();
73          if (null != output) {
74              output.flush();
75          }
76      }
77  
78      /**
79       * Writes byte to stream associated with current thread.
80       *
81       * @param ch
82       *            the byte to write to stream
83       * @throws IOException
84       *             if an error occurs
85       */
86      @Override
87      public void write(final int ch) throws IOException {
88          @SuppressWarnings("resource")
89          final OutputStream output = outputStreamThreadLocal.get();
90          if (null != output) {
91              output.write(ch);
92          }
93      }
94  }