001    /* BufferedWriter.java -- Buffer output into large blocks before writing
002       Copyright (C) 1998, 1999, 2000, 2001 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    /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
042     * "The Java Language Specification", ISBN 0-201-63451-1
043     * Status:  Complete to version 1.1.
044     */
045    
046    /**
047     * This class accumulates chars written in a buffer instead of immediately
048     * writing the data to the underlying output sink. The chars are instead
049     * as one large block when the buffer is filled, or when the stream is
050     * closed or explicitly flushed. This mode operation can provide a more
051     * efficient mechanism for writing versus doing numerous small unbuffered
052     * writes.
053     *
054     * @author Aaron M. Renn (arenn@urbanophile.com)
055     * @author Tom Tromey (tromey@cygnus.com)
056     * @date September 25, 1998 
057     */
058    public class BufferedWriter extends Writer
059    {
060      /**
061       * This is the default buffer size
062       */
063      private static final int DEFAULT_BUFFER_SIZE = 8192;
064    
065      /**
066       * This is the underlying <code>Writer</code> to which this object
067       * sends its output.
068       */
069      private Writer out;
070    
071      /**
072       * This is the internal char array used for buffering output before
073       * writing it.
074       */
075      char[] buffer;
076    
077      /**
078       * This is the number of chars that are currently in the buffer and
079       * are waiting to be written to the underlying stream.  It always points to
080       * the index into the buffer where the next char of data will be stored
081       */
082      int count;
083    
084      /**
085       * This method initializes a new <code>BufferedWriter</code> instance
086       * that will write to the specified subordinate <code>Writer</code>
087       * and which will use a default buffer size of 8192 chars.
088       *
089       * @param out The underlying <code>Writer</code> to write data to
090       */
091      public BufferedWriter (Writer out)
092      {
093        this (out, DEFAULT_BUFFER_SIZE);
094      }
095    
096      /**
097       * This method initializes a new <code>BufferedWriter</code> instance
098       * that will write to the specified subordinate <code>Writer</code>
099       * and which will use the specified buffer size
100       *
101       * @param out The underlying <code>Writer</code> to write data to
102       * @param size The size of the internal buffer
103       */
104      public BufferedWriter (Writer out, int size)
105      {
106        super(out.lock);
107        this.out = out;
108        this.buffer = new char[size];
109        this.count = 0;
110      }
111    
112      /**
113       * This method flushes any remaining buffered chars then closes the 
114       * underlying output stream.  Any further attempts to write to this stream
115       * may throw an exception
116       *
117       * @exception IOException If an error occurs.
118       */
119      public void close () throws IOException
120      {
121        synchronized (lock)
122          {
123            // It is safe to call localFlush even if the stream is already
124            // closed.
125            localFlush ();
126            out.close();
127            buffer = null;
128          }
129      }
130    
131      /**
132       * This method causes any currently buffered chars to be immediately
133       * written to the underlying output stream.
134       *
135       * @exception IOException If an error occurs
136       */
137      public void flush () throws IOException
138      {
139        synchronized (lock)
140          {
141            if (buffer == null)
142              throw new IOException ("Stream closed");
143            localFlush ();
144            out.flush();
145          }
146      }
147    
148      /**
149       * This method writes out a system depedent line separator sequence.  The
150       * actual value written is detemined from the <xmp>line.separator</xmp>
151       * system property.
152       *
153       * @exception IOException If an error occurs
154       */
155      public void newLine () throws IOException
156      {
157        write (System.getProperty("line.separator"));
158      }
159    
160      /**
161       * This method writes a single char of data.  This will be written to the
162       * buffer instead of the underlying data source.  However, if the buffer
163       * is filled as a result of this write request, it will be flushed to the
164       * underlying output stream.
165       *
166       * @param oneChar The char of data to be written, passed as an int
167       *
168       * @exception IOException If an error occurs
169       */
170      public void write (int oneChar) throws IOException
171      {
172        synchronized (lock)
173          {
174            if (buffer == null)
175              throw new IOException ("Stream closed");
176            buffer[count++] = (char) oneChar;
177            if (count == buffer.length)
178              localFlush ();
179          }
180      }
181    
182      /**
183       * This method writes <code>len</code> chars from the char array 
184       * <code>buf</code> starting at position <code>offset</code> in the buffer. 
185       * These chars will be written to the internal buffer.  However, if this
186       * write operation fills the buffer, the buffer will be flushed to the
187       * underlying output stream.
188       *
189       * @param buf The array of chars to write.
190       * @param offset The index into the char array to start writing from.
191       * @param len The number of chars to write.
192       *
193       * @exception IOException If an error occurs
194       */
195      public void write (char[] buf, int offset, int len) throws IOException
196      {
197        synchronized (lock)
198          {
199            if (buffer == null)
200              throw new IOException ("Stream closed");
201    
202            // Bypass buffering if there is too much incoming data.
203            if (count + len > buffer.length)
204              {
205                localFlush ();
206                out.write(buf, offset, len);
207              }
208            else
209              {
210                System.arraycopy(buf, offset, buffer, count, len);
211                count += len;
212                if (count == buffer.length)
213                  localFlush ();
214              }
215          }
216      }
217    
218      /**
219       * This method writes <code>len</code> chars from the <code>String</code>
220       * <code>str</code> starting at position <code>offset</code> in the string. 
221       * These chars will be written to the internal buffer.  However, if this
222       * write operation fills the buffer, the buffer will be flushed to the
223       * underlying output stream.
224       *
225       * @param str The <code>String</code> to write.
226       * @param offset The index into the string to start writing from.
227       * @param len The number of chars to write.
228       *
229       * @exception IOException If an error occurs
230       */
231      public void write (String str, int offset, int len) throws IOException
232      {
233        synchronized (lock)
234          {
235            if (buffer == null)
236              throw new IOException ("Stream closed");
237    
238            if (count + len > buffer.length)
239              {
240                localFlush ();
241                out.write(str, offset, len);
242              }
243            else
244              {
245                str.getChars(offset, offset + len, buffer, count);
246                count += len;
247                if (count == buffer.length)
248                  localFlush ();
249              }
250          }
251      }
252    
253      // This should only be called with the lock held.
254      private void localFlush () throws IOException
255      {
256        if (count > 0)
257          {
258            out.write(buffer, 0, count);
259            count = 0;
260          }
261      }
262    }