001    /* BufferedOutputStream.java -- Buffer output into large blocks before writing
002       Copyright (C) 1998, 2000, 2003 Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010     
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    
039    package java.io;
040    
041    /**
042      * This class accumulates bytes written in a buffer instead of immediately
043      * writing the data to the underlying output sink. The bytes are instead
044      * as one large block when the buffer is filled, or when the stream is
045      * closed or explicitly flushed. This mode operation can provide a more
046      * efficient mechanism for writing versus doing numerous small unbuffered
047      * writes.
048      *
049      * @author Aaron M. Renn (arenn@urbanophile.com)
050      */
051    public class BufferedOutputStream extends FilterOutputStream
052    {
053      /**
054       * This is the default buffer size
055       */
056      private static final int DEFAULT_BUFFER_SIZE = 512;
057    
058      /**
059       * This is the internal byte array used for buffering output before
060       * writing it.
061       */
062      protected byte[] buf;
063    
064      /**
065       * This is the number of bytes that are currently in the buffer and
066       * are waiting to be written to the underlying stream.  It always points to
067       * the index into the buffer where the next byte of data will be stored
068       */
069      protected int count;
070    
071      /**
072       * This method initializes a new <code>BufferedOutputStream</code> instance
073       * that will write to the specified subordinate <code>OutputStream</code>
074       * and which will use a default buffer size of 512 bytes.
075       *
076       * @param out The underlying <code>OutputStream</code> to write data to
077       */
078      public BufferedOutputStream(OutputStream out)
079      {
080        this(out, DEFAULT_BUFFER_SIZE);
081      }
082    
083      /**
084       * This method initializes a new <code>BufferedOutputStream</code> instance
085       * that will write to the specified subordinate <code>OutputStream</code>
086       * and which will use the specified buffer size
087       *
088       * @param out The underlying <code>OutputStream</code> to write data to
089       * @param size The size of the internal buffer
090       */
091      public BufferedOutputStream(OutputStream out, int size)
092      {
093        super(out);
094    
095        buf = new byte[size];
096      }
097    
098      /**
099       * This method causes any currently buffered bytes to be immediately
100       * written to the underlying output stream.
101       *
102       * @exception IOException If an error occurs
103       */
104      public synchronized void flush() throws IOException
105      {
106        if (count == 0)
107          return;
108    
109        out.write(buf, 0, count);
110        count = 0;
111        out.flush();
112      }
113    
114      /**
115       * This method flushes any remaining buffered bytes then closes the 
116       * underlying output stream.  Any further attempts to write to this stream
117       * may throw an exception
118       *
119      public synchronized void close() throws IOException
120      {
121        flush();
122        out.close();
123      }
124      */
125    
126      /**
127       * This method runs when the object is garbage collected.  It is 
128       * responsible for ensuring that all buffered bytes are written and
129       * for closing the underlying stream.
130       *
131       * @exception IOException If an error occurs (ignored by the Java runtime)
132       *
133      protected void finalize() throws IOException
134      {
135        close();
136      }
137      */
138    
139      /**
140       * This method writes a single byte of data.  This will be written to the
141       * buffer instead of the underlying data source.  However, if the buffer
142       * is filled as a result of this write request, it will be flushed to the
143       * underlying output stream.
144       *
145       * @param b The byte of data to be written, passed as an int
146       *
147       * @exception IOException If an error occurs
148       */
149      public synchronized void write(int b) throws IOException
150      {
151        if (count == buf.length)
152          flush();
153    
154        buf[count] = (byte)(b & 0xFF);
155        ++count;
156      }
157    
158      /**
159       * This method writes <code>len</code> bytes from the byte array 
160       * <code>buf</code> starting at position <code>offset</code> in the buffer. 
161       * These bytes will be written to the internal buffer.  However, if this
162       * write operation fills the buffer, the buffer will be flushed to the
163       * underlying output stream.
164       *
165       * @param buf The array of bytes to write.
166       * @param offset The index into the byte array to start writing from.
167       * @param len The number of bytes to write.
168       *
169       * @exception IOException If an error occurs
170       */
171      public synchronized void write(byte[] buf, int offset, int len) 
172        throws IOException
173      {
174        // Buffer can hold everything.  Note that the case where LEN < 0
175        // is automatically handled by the downstream write.
176        if (len < (this.buf.length - count))
177          {
178            System.arraycopy(buf, offset, this.buf, count, len);
179            count += len;
180          }
181        else
182          {
183            // The write was too big.  So flush the buffer and write the new
184            // bytes directly to the underlying stream, per the JDK 1.2
185            // docs.
186            flush();
187            out.write (buf, offset, len);
188          }
189      }
190    
191    } // class BufferedOutputStream 
192