libjava/classpath/java/io/BufferedWriter.java

   1 /* BufferedWriter.java -- Buffer output into large blocks before writing
   2    Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38
  39 package java.io;
  40
  41 /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
  42  * "The Java Language Specification", ISBN 0-201-63451-1
  43  * Status:  Complete to version 1.1.
  44  */
  45
  46 /**
  47  * This class accumulates chars written in a buffer instead of immediately
  48  * writing the data to the underlying output sink. The chars are instead
  49  * as one large block when the buffer is filled, or when the stream is
  50  * closed or explicitly flushed. This mode operation can provide a more
  51  * efficient mechanism for writing versus doing numerous small unbuffered
  52  * writes.
  53  *
  54  * @author Aaron M. Renn (arenn@urbanophile.com)
  55  * @author Tom Tromey (tromey@cygnus.com)
  56  * @date September 25, 1998
  57  */
  58 public class BufferedWriter extends Writer
  59 {
  60   /**
  61    * This is the default buffer size
  62    */
  63   private static final int DEFAULT_BUFFER_SIZE = 8192;
  64
  65   /**
  66    * This is the underlying <code>Writer</code> to which this object
  67    * sends its output.
  68    */
  69   private Writer out;
  70
  71   /**
  72    * This is the internal char array used for buffering output before
  73    * writing it.
  74    */
  75   char[] buffer;
  76
  77   /**
  78    * This is the number of chars that are currently in the buffer and
  79    * are waiting to be written to the underlying stream.  It always points to
  80    * the index into the buffer where the next char of data will be stored
  81    */
  82   int count;
  83
  84   /**
  85    * This method initializes a new <code>BufferedWriter</code> instance
  86    * that will write to the specified subordinate <code>Writer</code>
  87    * and which will use a default buffer size of 8192 chars.
  88    *
  89    * @param out The underlying <code>Writer</code> to write data to
  90    */
  91   public BufferedWriter (Writer out)
  92   {
  93     this (out, DEFAULT_BUFFER_SIZE);
  94   }
  95
  96   /**
  97    * This method initializes a new <code>BufferedWriter</code> instance
  98    * that will write to the specified subordinate <code>Writer</code>
  99    * 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 }