001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     * 
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     * 
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.commons.io.output;
018    
019    import java.io.IOException;
020    import java.io.OutputStream;
021    
022    /**
023     * Data written to this stream is forwarded to a stream that has been associated
024     * with this thread.
025     *
026     * @author <a href="mailto:peter@apache.org">Peter Donald</a>
027     * @version $Revision: 437567 $ $Date: 2006-08-28 07:39:07 +0100 (Mon, 28 Aug 2006) $
028     */
029    public class DemuxOutputStream
030        extends OutputStream
031    {
032        private InheritableThreadLocal m_streams = new InheritableThreadLocal();
033    
034        /**
035         * Bind the specified stream to the current thread.
036         *
037         * @param output the stream to bind
038         * @return the OutputStream that was previously active
039         */
040        public OutputStream bindStream( OutputStream output )
041        {
042            OutputStream stream = getStream();
043            m_streams.set( output );
044            return stream;
045        }
046    
047        /**
048         * Closes stream associated with current thread.
049         *
050         * @throws IOException if an error occurs
051         */
052        public void close()
053            throws IOException
054        {
055            OutputStream output = getStream();
056            if( null != output )
057            {
058                output.close();
059            }
060        }
061    
062        /**
063         * Flushes stream associated with current thread.
064         *
065         * @throws IOException if an error occurs
066         */
067        public void flush()
068            throws IOException
069        {
070            OutputStream output = getStream();
071            if( null != output )
072            {
073                output.flush();
074            }
075        }
076    
077        /**
078         * Writes byte to stream associated with current thread.
079         *
080         * @param ch the byte to write to stream
081         * @throws IOException if an error occurs
082         */
083        public void write( int ch )
084            throws IOException
085        {
086            OutputStream output = getStream();
087            if( null != output )
088            {
089                output.write( ch );
090            }
091        }
092    
093        /**
094         * Utility method to retrieve stream bound to current thread (if any).
095         *
096         * @return the output stream
097         */
098        private OutputStream getStream()
099        {
100            return (OutputStream)m_streams.get();
101        }
102    }