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1 771 jeremybenn
/* RandomAccessFile.java -- Class supporting random file I/O
2
   Copyright (C) 1998, 1999, 2001, 2002, 2003, 2004, 2005  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
import gnu.java.nio.FileChannelImpl;
42
 
43
import java.nio.channels.FileChannel;
44
 
45
/* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
46
 * "The Java Language Specification", ISBN 0-201-63451-1
47
 * Status: Believe complete and correct to 1.1.
48
 */
49
 
50
/**
51
 * This class allows reading and writing of files at random locations.
52
 * Most Java I/O classes are either pure sequential input or output.  This
53
 * class fulfills the need to be able to read the bytes of a file in an
54
 * arbitrary order.  In addition, this class implements the
55
 * <code>DataInput</code> and <code>DataOutput</code> interfaces to allow
56
 * the reading and writing of Java primitives.
57
 *
58
 * @author Aaron M. Renn (arenn@urbanophile.com)
59
 * @author Tom Tromey (tromey@cygnus.com)
60
 */
61
public class RandomAccessFile implements DataOutput, DataInput, Closeable
62
{
63
 
64
  // The underlying file.
65
  private FileChannelImpl ch;
66
  private FileDescriptor fd;
67
  // The corresponding input and output streams.
68
  private DataOutputStream out;
69
  private DataInputStream in;
70
 
71
 
72
  /**
73
   * This method initializes a new instance of <code>RandomAccessFile</code>
74
   * to read from the specified <code>File</code> object with the specified
75
   * access mode.   The access mode is either "r" for read only access or "rw"
76
   * for read-write access.
77
   * <p>
78
   * Note that a <code>SecurityManager</code> check is made prior to
79
   * opening the file to determine whether or not this file is allowed to
80
   * be read or written.
81
   *
82
   * @param file The <code>File</code> object to read and/or write.
83
   * @param mode "r" for read only or "rw" for read-write access to the file
84
   *
85
   * @exception IllegalArgumentException If <code>mode</code> has an
86
   * illegal value
87
   * @exception SecurityException If the requested access to the file
88
   * is not allowed
89
   * @exception FileNotFoundException If the file is a directory, or
90
   * any other error occurs
91
   */
92
  public RandomAccessFile (File file, String mode)
93
    throws FileNotFoundException
94
  {
95
    int fdmode;
96
    if (mode.equals("r"))
97
      fdmode = FileChannelImpl.READ;
98
    else if (mode.equals("rw"))
99
      fdmode = FileChannelImpl.READ | FileChannelImpl.WRITE;
100
    else if (mode.equals("rws"))
101
      {
102
        fdmode = (FileChannelImpl.READ | FileChannelImpl.WRITE
103
                  | FileChannelImpl.SYNC);
104
      }
105
    else if (mode.equals("rwd"))
106
      {
107
        fdmode = (FileChannelImpl.READ | FileChannelImpl.WRITE
108
                  | FileChannelImpl.DSYNC);
109
      }
110
    else
111
      throw new IllegalArgumentException ("invalid mode: " + mode);
112
 
113
    final String fileName = file.getPath();
114
 
115
    // The obligatory SecurityManager stuff
116
    SecurityManager s = System.getSecurityManager();
117
    if (s != null)
118
      {
119
        s.checkRead(fileName);
120
 
121
        if ((fdmode & FileChannelImpl.WRITE) != 0)
122
          s.checkWrite(fileName);
123
      }
124
 
125
    try
126
      {
127
        ch = FileChannelImpl.create(file, fdmode);
128
      }
129
    catch (FileNotFoundException fnfe)
130
      {
131
        throw fnfe;
132
      }
133
    catch (IOException ioe)
134
      {
135
        FileNotFoundException fnfe = new FileNotFoundException(file.getPath());
136
        fnfe.initCause(ioe);
137
        throw fnfe;
138
      }
139
    fd = new FileDescriptor(ch);
140
    if ((fdmode & FileChannelImpl.WRITE) != 0)
141
      out = new DataOutputStream (new FileOutputStream (fd));
142
    else
143
      out = null;
144
    in = new DataInputStream (new FileInputStream (fd));
145
  }
146
 
147
  /**
148
   * This method initializes a new instance of <code>RandomAccessFile</code>
149
   * to read from the specified file name with the specified access mode.
150
   * The access mode is either "r" for read only access, "rw" for read
151
   * write access, "rws" for synchronized read/write access of both
152
   * content and metadata, or "rwd" for read/write access
153
   * where only content is required to be synchronous.
154
   * <p>
155
   * Note that a <code>SecurityManager</code> check is made prior to
156
   * opening the file to determine whether or not this file is allowed to
157
   * be read or written.
158
   *
159
   * @param fileName The name of the file to read and/or write
160
   * @param mode "r", "rw", "rws", or "rwd"
161
   *
162
   * @exception IllegalArgumentException If <code>mode</code> has an
163
   * illegal value
164
   * @exception SecurityException If the requested access to the file
165
   * is not allowed
166
   * @exception FileNotFoundException If the file is a directory or
167
   * any other error occurs
168
   */
169
  public RandomAccessFile (String fileName, String mode)
170
    throws FileNotFoundException
171
  {
172
    this (new File(fileName), mode);
173
  }
174
 
175
  /**
176
   * This method closes the file and frees up all file related system
177
   * resources.  Since most operating systems put a limit on how many files
178
   * may be opened at any given time, it is a good idea to close all files
179
   * when no longer needed to avoid hitting this limit
180
   */
181
  public void close () throws IOException
182
  {
183
    ch.close();
184
  }
185
 
186
  /**
187
   * This method returns a <code>FileDescriptor</code> object that
188
   * represents the native file handle for this file.
189
   *
190
   * @return The <code>FileDescriptor</code> object for this file
191
   *
192
   * @exception IOException If an error occurs
193
   */
194
  public final FileDescriptor getFD () throws IOException
195
  {
196
    synchronized (this)
197
      {
198
        if (fd == null)
199
          fd = new FileDescriptor (ch);
200
        return fd;
201
      }
202
  }
203
 
204
  /**
205
   * This method returns the current offset in the file at which the next
206
   * read or write will occur
207
   *
208
   * @return The current file position
209
   *
210
   * @exception IOException If an error occurs
211
   */
212
  public long getFilePointer () throws IOException
213
  {
214
    return ch.position();
215
  }
216
 
217
  /**
218
   * This method sets the length of the file to the specified length.
219
   * If the currently length of the file is longer than the specified
220
   * length, then the file is truncated to the specified length (the
221
   * file position is set to the end of file in this case).  If the
222
   * current length of the file is shorter than the specified length,
223
   * the file is extended with bytes of an undefined value (the file
224
   * position is unchanged in this case).
225
   * <p>
226
   * The file must be open for write access for this operation to succeed.
227
   *
228
   * @param newLen The new length of the file
229
   *
230
   * @exception IOException If an error occurs
231
   */
232
  public void setLength (long newLen) throws IOException
233
  {
234
    // FIXME: Extending a file should probably be done by one method call.
235
 
236
    // FileChannel.truncate() can only shrink a file.
237
    // To expand it we need to seek forward and write at least one byte.
238
    if (newLen < length())
239
      ch.truncate (newLen);
240
    else if (newLen > length())
241
      {
242
        long pos = getFilePointer();
243
        seek(newLen - 1);
244
        write(0);
245
        seek(pos);
246
      }
247
  }
248
 
249
  /**
250
   * This method returns the length of the file in bytes
251
   *
252
   * @return The length of the file
253
   *
254
   * @exception IOException If an error occurs
255
   */
256
  public long length () throws IOException
257
  {
258
    return ch.size();
259
  }
260
 
261
  /**
262
   * This method reads a single byte of data from the file and returns it
263
   * as an integer.
264
   *
265
   * @return The byte read as an int, or -1 if the end of the file was reached.
266
   *
267
   * @exception IOException If an error occurs
268
   */
269
  public int read () throws IOException
270
  {
271
    return in.read();
272
  }
273
 
274
  /**
275
   * This method reads bytes from the file into the specified array.  The
276
   * bytes are stored starting at the beginning of the array and up to
277
   * <code>buf.length</code> bytes can be read.
278
   *
279
   * @param buffer The buffer to read bytes from the file into
280
   *
281
   * @return The actual number of bytes read or -1 if end of file
282
   *
283
   * @exception IOException If an error occurs
284
   */
285
  public int read (byte[] buffer) throws IOException
286
  {
287
    return in.read (buffer);
288
  }
289
 
290
  /**
291
   * This methods reads up to <code>len</code> bytes from the file into the
292
   * specified array starting at position <code>offset</code> into the array.
293
   *
294
   * @param buffer The array to read the bytes into
295
   * @param offset The index into the array to start storing bytes
296
   * @param len The requested number of bytes to read
297
   *
298
   * @return The actual number of bytes read, or -1 if end of file
299
   *
300
   * @exception IOException If an error occurs
301
   */
302
  public int read (byte[] buffer, int offset, int len) throws IOException
303
  {
304
    return in.read (buffer, offset, len);
305
  }
306
 
307
  /**
308
   * This method reads a Java boolean value from an input stream.  It does
309
   * so by reading a single byte of data.  If that byte is zero, then the
310
   * value returned is <code>false</code>  If the byte is non-zero, then
311
   * the value returned is <code>true</code>
312
   * <p>
313
   * This method can read a <code>boolean</code> written by an object
314
   * implementing the
315
   * <code>writeBoolean()</code> method in the <code>DataOutput</code>
316
   * interface.
317
   *
318
   * @return The <code>boolean</code> value read
319
   *
320
   * @exception EOFException If end of file is reached before reading the
321
   * boolean
322
   * @exception IOException If any other error occurs
323
   */
324
  public final boolean readBoolean () throws IOException
325
  {
326
    return in.readBoolean ();
327
  }
328
 
329
  /**
330
   * This method reads a Java byte value from an input stream.  The value
331
   * is in the range of -128 to 127.
332
   * <p>
333
   * This method can read a <code>byte</code> written by an object
334
   * implementing the
335
   * <code>writeByte()</code> method in the <code>DataOutput</code> interface.
336
   *
337
   * @return The <code>byte</code> value read
338
   *
339
   * @exception EOFException If end of file is reached before reading the byte
340
   * @exception IOException If any other error occurs
341
   *
342
   * @see DataOutput
343
   */
344
  public final byte readByte () throws IOException
345
  {
346
    return in.readByte ();
347
  }
348
 
349
  /**
350
   * This method reads a Java <code>char</code> value from an input stream.
351
   * It operates by reading two bytes from the stream and converting them to
352
   * a single 16-bit Java <code>char</code>  The two bytes are stored most
353
   * significant byte first (i.e., "big endian") regardless of the native
354
   * host byte ordering.
355
   * <p>
356
   * As an example, if <code>byte1</code> and <code>byte2</code> represent
357
   * the first
358
   * and second byte read from the stream respectively, they will be
359
   * transformed to a <code>char</code> in the following manner:
360
   * <p>
361
   * <code>(char)(((byte1 &amp; 0xFF) &lt;&lt; 8) | (byte2 &amp; 0xFF)</code>
362
   * <p>
363
   * This method can read a <code>char</code> written by an object
364
   * implementing the
365
   * <code>writeChar()</code> method in the <code>DataOutput</code> interface.
366
   *
367
   * @return The <code>char</code> value read
368
   *
369
   * @exception EOFException If end of file is reached before reading the char
370
   * @exception IOException If any other error occurs
371
   *
372
   * @see DataOutput
373
   */
374
  public final char readChar () throws IOException
375
  {
376
    return in.readChar();
377
  }
378
 
379
  /**
380
   * This method reads a Java double value from an input stream.  It operates
381
   * by first reading a <code>logn</code> value from the stream by calling the
382
   * <code>readLong()</code> method in this interface, then
383
   * converts that <code>long</code>
384
   * to a <code>double</code> using the <code>longBitsToDouble</code>
385
   * method in the class <code>java.lang.Double</code>
386
   * <p>
387
   * This method can read a <code>double</code> written by an object
388
   * implementing the
389
   * <code>writeDouble()</code> method in the <code>DataOutput</code>
390
   * interface.
391
   *
392
   * @return The <code>double</code> value read
393
   *
394
   * @exception EOFException If end of file is reached before reading
395
   * the double
396
   * @exception IOException If any other error occurs
397
   *
398
   * @see java.lang.Double
399
   * @see DataOutput
400
   */
401
  public final double readDouble () throws IOException
402
  {
403
    return in.readDouble ();
404
  }
405
 
406
  /**
407
   * This method reads a Java float value from an input stream.  It operates
408
   * by first reading an <code>int</code> value from the stream by calling the
409
   * <code>readInt()</code> method in this interface, then converts
410
   * that <code>int</code>
411
   * to a <code>float</code> using the <code>intBitsToFloat</code> method in
412
   * the class <code>java.lang.Float</code>
413
   * <p>
414
   * This method can read a <code>float</code> written by an object
415
   * implementing the
416
   * <code>writeFloat()</code> method in the <code>DataOutput</code> interface.
417
   *
418
   * @return The <code>float</code> value read
419
   *
420
   * @exception EOFException If end of file is reached before reading the float
421
   * @exception IOException If any other error occurs
422
   *
423
   * @see java.lang.Float
424
   * @see DataOutput
425
   */
426
  public final float readFloat () throws IOException
427
  {
428
    return in.readFloat();
429
  }
430
 
431
  /**
432
   * This method reads raw bytes into the passed array until the array is
433
   * full.  Note that this method blocks until the data is available and
434
   * throws an exception if there is not enough data left in the stream to
435
   * fill the buffer
436
   *
437
   * @param buffer The buffer into which to read the data
438
   *
439
   * @exception EOFException If end of file is reached before filling the
440
   * buffer
441
   * @exception IOException If any other error occurs
442
   */
443
  public final void readFully (byte[] buffer) throws IOException
444
  {
445
    in.readFully(buffer);
446
  }
447
 
448
  /**
449
   * This method reads raw bytes into the passed array <code>buf</code>
450
   * starting
451
   * <code>offset</code> bytes into the buffer.  The number of bytes read
452
   * will be
453
   * exactly <code>len</code>  Note that this method blocks until the data is
454
   * available and throws an exception if there is not enough data left in
455
   * the stream to read <code>len</code> bytes.
456
   *
457
   * @param buffer The buffer into which to read the data
458
   * @param offset The offset into the buffer to start storing data
459
   * @param count The number of bytes to read into the buffer
460
   *
461
   * @exception EOFException If end of file is reached before filling
462
   * the buffer
463
   * @exception IOException If any other error occurs
464
   */
465
  public final void readFully (byte[] buffer, int offset, int count)
466
    throws IOException
467
  {
468
    in.readFully (buffer, offset, count);
469
  }
470
 
471
  /**
472
   * This method reads a Java <code>int</code> value from an input stream
473
   * It operates by reading four bytes from the stream and converting them to
474
   * a single Java <code>int</code>  The bytes are stored most
475
   * significant byte first (i.e., "big endian") regardless of the native
476
   * host byte ordering.
477
   * <p>
478
   * As an example, if <code>byte1</code> through <code>byte4</code>
479
   * represent the first
480
   * four bytes read from the stream, they will be
481
   * transformed to an <code>int</code> in the following manner:
482
   * <p>
483
   * <code>(int)(((byte1 &amp; 0xFF) &lt;&lt; 24) + ((byte2 &amp; 0xFF) &lt;&lt; 16) +
484
   * ((byte3 &amp; 0xFF) &lt;&lt; 8) + (byte4 &amp; 0xFF)))</code>
485
   * <p>
486
   * The value returned is in the range of 0 to 65535.
487
   * <p>
488
   * This method can read an <code>int</code> written by an object
489
   * implementing the
490
   * <code>writeInt()</code> method in the <code>DataOutput</code> interface.
491
   *
492
   * @return The <code>int</code> value read
493
   *
494
   * @exception EOFException If end of file is reached before reading the int
495
   * @exception IOException If any other error occurs
496
   *
497
   * @see DataOutput
498
   */
499
  public final int readInt () throws IOException
500
  {
501
    return in.readInt();
502
  }
503
 
504
  /**
505
   * This method reads the next line of text data from an input stream.
506
   * It operates by reading bytes and converting those bytes to
507
   * <code>char</code>
508
   * values by treating the byte read as the low eight bits of the
509
   * <code>char</code>
510
   * and using <code>0</code> as the high eight bits.  Because of this, it does
511
   * not support the full 16-bit Unicode character set.
512
   * <p>
513
   * The reading of bytes ends when either the end of file or a line terminator
514
   * is encountered.  The bytes read are then returned as a <code>String</code>
515
   * A line terminator is a byte sequence consisting of either
516
   * <code>\r</code> <code>\n</code> or <code>\r\n</code>  These
517
   * termination charaters are
518
   * discarded and are not returned as part of the string.
519
   * <p>
520
   * This method can read data that was written by an object implementing the
521
   * <code>writeLine()</code> method in <code>DataOutput</code>
522
   *
523
   * @return The line read as a <code>String</code>
524
   *
525
   * @exception IOException If an error occurs
526
   *
527
   * @see DataOutput
528
   */
529
  public final String readLine () throws IOException
530
  {
531
    return in.readLine ();
532
  }
533
 
534
  /**
535
   * This method reads a Java long value from an input stream
536
   * It operates by reading eight bytes from the stream and converting them to
537
   * a single Java <code>long</code>  The bytes are stored most
538
   * significant byte first (i.e., "big endian") regardless of the native
539
   * host byte ordering.
540
   * <p>
541
   * As an example, if <code>byte1</code> through <code>byte8</code>
542
   * represent the first
543
   * eight bytes read from the stream, they will be
544
   * transformed to an <code>long</code> in the following manner:
545
   * <p>
546
   * <code>
547
   * (long)((((long)byte1 &amp; 0xFF) &lt;&lt; 56) + (((long)byte2 &amp; 0xFF) &lt;&lt; 48) +
548
   * (((long)byte3 &amp; 0xFF) &lt;&lt; 40) + (((long)byte4 &amp; 0xFF) &lt;&lt; 32) +
549
   * (((long)byte5 &amp; 0xFF) &lt;&lt; 24) + (((long)byte6 &amp; 0xFF) &lt;&lt; 16) +
550
   * (((long)byte7 &amp; 0xFF) &lt;&lt; 8) + ((long)byte9 &amp; 0xFF)))</code>
551
   * <p>
552
   * The value returned is in the range of 0 to 65535.
553
   * <p>
554
   * This method can read an <code>long</code> written by an object
555
   * implementing the
556
   * <code>writeLong()</code> method in the <code>DataOutput</code> interface.
557
   *
558
   * @return The <code>long</code> value read
559
   *
560
   * @exception EOFException If end of file is reached before reading the long
561
   * @exception IOException If any other error occurs
562
   *
563
   * @see DataOutput
564
   */
565
  public final long readLong () throws IOException
566
  {
567
    return in.readLong();
568
  }
569
 
570
  /**
571
   * This method reads a signed 16-bit value into a Java in from the stream.
572
   * It operates by reading two bytes from the stream and converting them to
573
   * a single 16-bit Java <code>short</code>  The two bytes are stored most
574
   * significant byte first (i.e., "big endian") regardless of the native
575
   * host byte ordering.
576
   * <p>
577
   * As an example, if <code>byte1</code> and <code>byte2</code>
578
   * represent the first
579
   * and second byte read from the stream respectively, they will be
580
   * transformed to a <code>short</code> in the following manner:
581
   * <p>
582
   * <code>(short)(((byte1 &amp; 0xFF) &lt;&lt; 8) | (byte2 &amp; 0xFF)</code>
583
   * <p>
584
   * The value returned is in the range of -32768 to 32767.
585
   * <p>
586
   * This method can read a <code>short</code> written by an object
587
   * implementing the
588
   * <code>writeShort()</code> method in the <code>DataOutput</code> interface.
589
   *
590
   * @return The <code>short</code> value read
591
   *
592
   * @exception EOFException If end of file is reached before reading the value
593
   * @exception IOException If any other error occurs
594
   *
595
   * @see DataOutput
596
   */
597
  public final short readShort () throws IOException
598
  {
599
    return in.readShort();
600
  }
601
 
602
  /**
603
   * This method reads 8 unsigned bits into a Java <code>int</code> value
604
   * from the
605
   * stream. The value returned is in the range of 0 to 255.
606
   * <p>
607
   * This method can read an unsigned byte written by an object implementing
608
   * the <code>writeUnsignedByte()</code> method in the
609
   * <code>DataOutput</code> interface.
610
   *
611
   * @return The unsigned bytes value read as a Java <code>int</code>
612
   *
613
   * @exception EOFException If end of file is reached before reading the value
614
   * @exception IOException If any other error occurs
615
   *
616
   * @see DataOutput
617
   */
618
  public final int readUnsignedByte () throws IOException
619
  {
620
    return in.readUnsignedByte();
621
  }
622
 
623
  /**
624
   * This method reads 16 unsigned bits into a Java int value from the stream.
625
   * It operates by reading two bytes from the stream and converting them to
626
   * a single Java <code>int</code>  The two bytes are stored most
627
   * significant byte first (i.e., "big endian") regardless of the native
628
   * host byte ordering.
629
   * <p>
630
   * As an example, if <code>byte1</code> and <code>byte2</code>
631
   * represent the first
632
   * and second byte read from the stream respectively, they will be
633
   * transformed to an <code>int</code> in the following manner:
634
   * <p>
635
   * <code>(int)(((byte1 &amp; 0xFF) &lt;&lt; 8) + (byte2 &amp; 0xFF))</code>
636
   * <p>
637
   * The value returned is in the range of 0 to 65535.
638
   * <p>
639
   * This method can read an unsigned short written by an object implementing
640
   * the <code>writeUnsignedShort()</code> method in the
641
   * <code>DataOutput</code> interface.
642
   *
643
   * @return The unsigned short value read as a Java <code>int</code>
644
   *
645
   * @exception EOFException If end of file is reached before reading the value
646
   * @exception IOException If any other error occurs
647
   */
648
  public final int readUnsignedShort () throws IOException
649
  {
650
    return in.readUnsignedShort();
651
  }
652
 
653
  /**
654
   * This method reads a <code>String</code> from an input stream that
655
   * is encoded in
656
   * a modified UTF-8 format.  This format has a leading two byte sequence
657
   * that contains the remaining number of bytes to read.  This two byte
658
   * sequence is read using the <code>readUnsignedShort()</code> method of this
659
   * interface.
660
   * <p>
661
   * After the number of remaining bytes have been determined, these bytes
662
   * are read an transformed into <code>char</code> values.
663
   * These <code>char</code> values
664
   * are encoded in the stream using either a one, two, or three byte format.
665
   * The particular format in use can be determined by examining the first
666
   * byte read.
667
   * <p>
668
   * If the first byte has a high order bit of 0 then
669
   * that character consists on only one byte.  This character value consists
670
   * of seven bits that are at positions 0 through 6 of the byte.  As an
671
   * example, if <code>byte1</code> is the byte read from the stream, it would
672
   * be converted to a <code>char</code> like so:
673
   * <p>
674
   * <code>(char)byte1</code>
675
   * <p>
676
   * If the first byte has <code>110</code> as its high order bits, then the
677
   * character consists of two bytes.  The bits that make up the character
678
   * value are in positions 0 through 4 of the first byte and bit positions
679
   * 0 through 5 of the second byte.  (The second byte should have
680
   * 10 as its high order bits).  These values are in most significant
681
   * byte first (i.e., "big endian") order.
682
   * <p>
683
   * As an example, if <code>byte1</code> and <code>byte2</code>
684
   * are the first two bytes
685
   * read respectively, and the high order bits of them match the patterns
686
   * which indicate a two byte character encoding, then they would be
687
   * converted to a Java <code>char</code> like so:
688
   * <p>
689
   * <code>(char)(((byte1 & 0x1F) << 6) | (byte2 & 0x3F))</code>
690
   * <p>
691
   * If the first byte has a <code>1110</code> as its high order bits, then the
692
   * character consists of three bytes.  The bits that make up the character
693
   * value are in positions 0 through 3 of the first byte and bit positions
694
   * 0 through 5 of the other two bytes.  (The second and third bytes should
695
   * have <code>10</code> as their high order bits).  These values are in most
696
   * significant byte first (i.e., "big endian") order.
697
   * <p>
698
   * As an example, if <code>byte1</code> <code>byte2</code>
699
   * and <code>byte3</code> are the
700
   * three bytes read, and the high order bits of them match the patterns
701
   * which indicate a three byte character encoding, then they would be
702
   * converted to a Java <code>char</code> like so:
703
   * <p>
704
   * <code>(char)(((byte1 & 0x0F) << 12) | ((byte2 & 0x3F) << 6) |
705
   * (byte3 & 0x3F))</code>
706
   * <p>
707
   * Note that all characters are encoded in the method that requires the
708
   * fewest number of bytes with the exception of the character with the
709
   * value of <code>&#92;u0000</code> which is encoded as two bytes.  This is
710
   * a  modification of the UTF standard used to prevent C language style
711
   * <code>NUL</code> values from appearing in the byte stream.
712
   * <p>
713
   * This method can read data that was written by an object implementing the
714
   * <code>writeUTF()</code> method in <code>DataOutput</code>
715
   *
716
   * @return The <code>String</code> read
717
   *
718
   * @exception EOFException If end of file is reached before reading the
719
   * String
720
   * @exception UTFDataFormatException If the data is not in UTF-8 format
721
   * @exception IOException If any other error occurs
722
   *
723
   * @see DataOutput
724
   */
725
  public final String readUTF () throws IOException
726
  {
727
    return in.readUTF();
728
  }
729
 
730
  /**
731
   * This method sets the current file position to the specified offset
732
   * from the beginning of the file.  Note that some operating systems will
733
   * allow the file pointer to be set past the current end of the file.
734
   *
735
   * @param pos The offset from the beginning of the file at which to set
736
   * the file pointer
737
   *
738
   * @exception IOException If an error occurs
739
   */
740
  public void seek (long pos) throws IOException
741
  {
742
    ch.position(pos);
743
  }
744
 
745
  /**
746
   * This method attempts to skip and discard the specified number of bytes
747
   * in the input stream.  It may actually skip fewer bytes than requested.
748
   * The actual number of bytes skipped is returned.  This method will not
749
   * skip any bytes if passed a negative number of bytes to skip.
750
   *
751
   * @param numBytes The requested number of bytes to skip.
752
   *
753
   * @return The number of bytes actually skipped.
754
   *
755
   * @exception IOException If an error occurs.
756
   */
757
  public int skipBytes (int numBytes) throws IOException
758
  {
759
    if (numBytes < 0)
760
      throw new IllegalArgumentException ("Can't skip negative bytes: " +
761
                                          numBytes);
762
 
763
    if (numBytes == 0)
764
      return 0;
765
 
766
    long oldPos = ch.position();
767
    long newPos = oldPos + numBytes;
768
    long size = ch.size();
769
    if (newPos > size)
770
      newPos = size;
771
    ch.position(newPos);
772
    return (int) (ch.position() - oldPos);
773
  }
774
 
775
  /**
776
   * This method writes a single byte of data to the file. The file must
777
   * be open for read-write in order for this operation to succeed.
778
   *
779
   * @param oneByte The byte of data to write, passed as an int.
780
   *
781
   * @exception IOException If an error occurs
782
   */
783
  public void write (int oneByte) throws IOException
784
  {
785
    if (out == null)
786
      throw new IOException("Bad file descriptor");
787
 
788
    out.write(oneByte);
789
  }
790
 
791
  /**
792
   * This method writes all the bytes in the specified array to the file.
793
   * The file must be open read-write in order for this operation to succeed.
794
   *
795
   * @param buffer The array of bytes to write to the file
796
   */
797
  public void write (byte[] buffer) throws IOException
798
  {
799
    if (out == null)
800
      throw new IOException("Bad file descriptor");
801
 
802
    out.write(buffer);
803
  }
804
 
805
  /**
806
   * This method writes <code>len</code> bytes to the file from the specified
807
   * array starting at index <code>offset</code> into the array.
808
   *
809
   * @param buffer The array of bytes to write to the file
810
   * @param offset The index into the array to start writing file
811
   * @param len The number of bytes to write
812
   *
813
   * @exception IOException If an error occurs
814
   */
815
  public void write (byte[] buffer, int offset, int len) throws IOException
816
  {
817
    if (out == null)
818
      throw new IOException("Bad file descriptor");
819
 
820
    out.write (buffer, offset, len);
821
  }
822
 
823
  /**
824
   * This method writes a Java <code>boolean</code> to the underlying output
825
   * stream. For a value of <code>true</code>, 1 is written to the stream.
826
   * For a value of <code>false</code>, 0 is written.
827
   *
828
   * @param val The <code>boolean</code> value to write to the stream
829
   *
830
   * @exception IOException If an error occurs
831
   */
832
  public final void writeBoolean (boolean val) throws IOException
833
  {
834
    if (out == null)
835
      throw new IOException("Bad file descriptor");
836
 
837
    out.writeBoolean(val);
838
  }
839
 
840
  /**
841
   * This method writes a Java <code>byte</code> value to the underlying
842
   * output stream.
843
   *
844
   * @param val The <code>byte</code> to write to the stream, passed
845
   * as an <code>int</code>.
846
   *
847
   * @exception IOException If an error occurs
848
   */
849
  public final void writeByte (int val) throws IOException
850
  {
851
    if (out == null)
852
      throw new IOException("Bad file descriptor");
853
 
854
    out.writeByte(val);
855
  }
856
 
857
  /**
858
   * This method writes a Java <code>short</code> to the stream, high byte
859
   * first.  This method requires two bytes to encode the value.
860
   *
861
   * @param val The <code>short</code> value to write to the stream,
862
   * passed as an <code>int</code>.
863
   *
864
   * @exception IOException If an error occurs
865
   */
866
  public final void writeShort (int val) throws IOException
867
  {
868
    if (out == null)
869
      throw new IOException("Bad file descriptor");
870
 
871
    out.writeShort(val);
872
  }
873
 
874
  /**
875
   * This method writes a single <code>char</code> value to the stream,
876
   * high byte first.
877
   *
878
   * @param val The <code>char</code> value to write, passed as
879
   * an <code>int</code>.
880
   *
881
   * @exception IOException If an error occurs
882
   */
883
  public final void writeChar (int val) throws IOException
884
  {
885
    if (out == null)
886
      throw new IOException("Bad file descriptor");
887
 
888
    out.writeChar(val);
889
  }
890
 
891
  /**
892
   * This method writes a Java <code>int</code> to the stream, high bytes
893
   * first.  This method requires four bytes to encode the value.
894
   *
895
   * @param val The <code>int</code> value to write to the stream.
896
   *
897
   * @exception IOException If an error occurs
898
   */
899
  public final void writeInt (int val) throws IOException
900
  {
901
    if (out == null)
902
      throw new IOException("Bad file descriptor");
903
 
904
    out.writeInt(val);
905
  }
906
 
907
  /**
908
   * This method writes a Java <code>long</code> to the stream, high bytes
909
   * first.  This method requires eight bytes to encode the value.
910
   *
911
   * @param val The <code>long</code> value to write to the stream.
912
   *
913
   * @exception IOException If an error occurs
914
   */
915
  public final void writeLong (long val) throws IOException
916
  {
917
    if (out == null)
918
      throw new IOException("Bad file descriptor");
919
 
920
    out.writeLong(val);
921
  }
922
 
923
  /**
924
   * This method writes a Java <code>float</code> value to the stream.  This
925
   * value is written by first calling the method
926
   * <code>Float.floatToIntBits</code>
927
   * to retrieve an <code>int</code> representing the floating point number,
928
   * then writing this <code>int</code> value to the stream exactly the same
929
   * as the <code>writeInt()</code> method does.
930
   *
931
   * @param val The floating point number to write to the stream.
932
   *
933
   * @exception IOException If an error occurs
934
   *
935
   * @see #writeInt(int)
936
   */
937
  public final void writeFloat (float val) throws IOException
938
  {
939
    if (out == null)
940
      throw new IOException("Bad file descriptor");
941
 
942
    out.writeFloat(val);
943
  }
944
 
945
  /**
946
   * This method writes a Java <code>double</code> value to the stream.  This
947
   * value is written by first calling the method
948
   * <code>Double.doubleToLongBits</code>
949
   * to retrieve an <code>long</code> representing the floating point number,
950
   * then writing this <code>long</code> value to the stream exactly the same
951
   * as the <code>writeLong()</code> method does.
952
   *
953
   * @param val The double precision floating point number to write to the
954
   * stream.
955
   *
956
   * @exception IOException If an error occurs
957
   *
958
   * @see #writeLong(long)
959
   */
960
  public final void writeDouble (double val) throws IOException
961
  {
962
    if (out == null)
963
      throw new IOException("Bad file descriptor");
964
 
965
    out.writeDouble(val);
966
  }
967
 
968
  /**
969
   * This method writes all the bytes in a <code>String</code> out to the
970
   * stream.  One byte is written for each character in the <code>String</code>.
971
   * The high eight bits of each character are discarded.
972
   *
973
   * @param val The <code>String</code> to write to the stream
974
   *
975
   * @exception IOException If an error occurs
976
   */
977
  public final void writeBytes (String val) throws IOException
978
  {
979
    if (out == null)
980
      throw new IOException("Bad file descriptor");
981
 
982
    out.writeBytes(val);
983
  }
984
 
985
  /**
986
   * This method writes all the characters in a <code>String</code> to the
987
   * stream.  There will be two bytes for each character value.  The high
988
   * byte of the character will be written first.
989
   *
990
   * @param val The <code>String</code> to write to the stream.
991
   *
992
   * @exception IOException If an error occurs
993
   */
994
  public final void writeChars (String val) throws IOException
995
  {
996
    if (out == null)
997
      throw new IOException("Bad file descriptor");
998
 
999
    out.writeChars(val);
1000
  }
1001
 
1002
  /**
1003
   * This method writes a Java <code>String</code> to the stream in a modified
1004
   * UTF-8 format.  First, two bytes are written to the stream indicating the
1005
   * number of bytes to follow.  Note that this is the number of bytes in the
1006
   * encoded <code>String</code> not the <code>String</code> length.  Next
1007
   * come the encoded characters.  Each character in the <code>String</code>
1008
   * is encoded as either one, two or three bytes.  For characters in the
1009
   * range of <code>&#92;u0001</code> to <code>&#92;u007F</code>,
1010
   * one byte is used.  The character
1011
   * value goes into bits 0-7 and bit eight is 0.  For characters in the range
1012
   * of <code>&#92;u0080</code> to <code>&#92;u007FF</code>, two
1013
   * bytes are used.  Bits
1014
   * 6-10 of the character value are encoded bits 0-4 of the first byte, with
1015
   * the high bytes having a value of "110".  Bits 0-5 of the character value
1016
   * are stored in bits 0-5 of the second byte, with the high bits set to
1017
   * "10".  This type of encoding is also done for the null character
1018
   * <code>&#92;u0000</code>.  This eliminates any C style NUL character values
1019
   * in the output.  All remaining characters are stored as three bytes.
1020
   * Bits 12-15 of the character value are stored in bits 0-3 of the first
1021
   * byte.  The high bits of the first bytes are set to "1110".  Bits 6-11
1022
   * of the character value are stored in bits 0-5 of the second byte.  The
1023
   * high bits of the second byte are set to "10".  And bits 0-5 of the
1024
   * character value are stored in bits 0-5 of byte three, with the high bits
1025
   * of that byte set to "10".
1026
   *
1027
   * @param val The <code>String</code> to write to the output in UTF format
1028
   *
1029
   * @exception IOException If an error occurs
1030
   */
1031
  public final void writeUTF (String val) throws IOException
1032
  {
1033
    if (out == null)
1034
      throw new IOException("Bad file descriptor");
1035
 
1036
    out.writeUTF(val);
1037
  }
1038
 
1039
  /**
1040
   * This method creates a java.nio.channels.FileChannel.
1041
   * Nio does not allow one to create a file channel directly.
1042
   * A file channel must be created by first creating an instance of
1043
   * Input/Output/RandomAccessFile and invoking the getChannel() method on it.
1044
   */
1045
  public final synchronized FileChannel getChannel ()
1046
  {
1047
    return ch;
1048
  }
1049
}

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