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: 736890 $ $Date: 2009-01-22 21:02:22 -0500 (Thu, 22 Jan 2009) $
028     */
029    public class DemuxOutputStream
030        extends OutputStream
031    {
032        private final InheritableThreadLocal<OutputStream> m_streams = new InheritableThreadLocal<OutputStream>();
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 = m_streams.get();
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        @Override
053        public void close()
054            throws IOException
055        {
056            OutputStream output = m_streams.get();
057            if( null != output )
058            {
059                output.close();
060            }
061        }
062    
063        /**
064         * Flushes stream associated with current thread.
065         *
066         * @throws IOException if an error occurs
067         */
068        @Override
069        public void flush()
070            throws IOException
071        {
072            OutputStream output = m_streams.get();
073            if( null != output )
074            {
075                output.flush();
076            }
077        }
078    
079        /**
080         * Writes byte to stream associated with current thread.
081         *
082         * @param ch the byte to write to stream
083         * @throws IOException if an error occurs
084         */
085        @Override
086        public void write( int ch )
087            throws IOException
088        {
089            OutputStream output = m_streams.get();
090            if( null != output )
091            {
092                output.write( ch );
093            }
094        }
095    }