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 07:39:07 +0100 (Mon, 28 Aug 2006) $
28  */
29 public class DemuxOutputStream
30     extends OutputStream
31 {
32     private InheritableThreadLocal<OutputStream> m_streams = new InheritableThreadLocal<OutputStream>();
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      */
bindStream( OutputStream output )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     @Override
close()53     public void close()
54         throws IOException
55     {
56         OutputStream output = getStream();
57         if( null != output )
58         {
59             output.close();
60         }
61     }
62 
63     /**
64      * Flushes stream associated with current thread.
65      *
66      * @throws IOException if an error occurs
67      */
68     @Override
flush()69     public void flush()
70         throws IOException
71     {
72         OutputStream output = getStream();
73         if( null != output )
74         {
75             output.flush();
76         }
77     }
78 
79     /**
80      * Writes byte to stream associated with current thread.
81      *
82      * @param ch the byte to write to stream
83      * @throws IOException if an error occurs
84      */
85     @Override
write( int ch )86     public void write( int ch )
87         throws IOException
88     {
89         OutputStream output = getStream();
90         if( null != output )
91         {
92             output.write( ch );
93         }
94     }
95 
96     /**
97      * Utility method to retrieve stream bound to current thread (if any).
98      *
99      * @return the output stream
100      */
getStream()101     private OutputStream getStream()
102     {
103         return m_streams.get();
104     }
105 }
106