libjava/classpath/java/io/RandomAccessFile.java

   1 /* 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 }