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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  /**
23   * Data written to this stream is forwarded to a stream that has been associated
24   * with this thread.
25   *
26   * @author <a href="mailto:peter@apache.org">Peter Donald</a>
27   * @version $Revision: 437567 $ $Date: 2006-08-28 08:39:07 +0200 (Mo, 28 Aug 2006) $
28   */
29  public class DemuxOutputStream
30      extends OutputStream
31  {
32      private InheritableThreadLocal m_streams = new InheritableThreadLocal();
33  
34      /**
35       * Bind the specified stream to the current thread.
36       *
37       * @param output the stream to bind
38       * @return the OutputStream that was previously active
39       */
40      public OutputStream bindStream( OutputStream output )
41      {
42          OutputStream stream = getStream();
43          m_streams.set( output );
44          return stream;
45      }
46  
47      /**
48       * Closes stream associated with current thread.
49       *
50       * @throws IOException if an error occurs
51       */
52      public void close()
53          throws IOException
54      {
55          OutputStream output = getStream();
56          if( null != output )
57          {
58              output.close();
59          }
60      }
61  
62      /**
63       * Flushes stream associated with current thread.
64       *
65       * @throws IOException if an error occurs
66       */
67      public void flush()
68          throws IOException
69      {
70          OutputStream output = getStream();
71          if( null != output )
72          {
73              output.flush();
74          }
75      }
76  
77      /**
78       * Writes byte to stream associated with current thread.
79       *
80       * @param ch the byte to write to stream
81       * @throws IOException if an error occurs
82       */
83      public void write( int ch )
84          throws IOException
85      {
86          OutputStream output = getStream();
87          if( null != output )
88          {
89              output.write( ch );
90          }
91      }
92  
93      /**
94       * Utility method to retrieve stream bound to current thread (if any).
95       *
96       * @return the output stream
97       */
98      private OutputStream getStream()
99      {
100         return (OutputStream)m_streams.get();
101     }
102 }