libjava/java/io/FileDescriptor.java

   1 /* FileDescriptor.java -- Opaque file handle class
   2    Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004
   3    Free Software Foundation, Inc.
   4
   5 This file is part of GNU Classpath.
   6
   7 GNU Classpath is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2, or (at your option)
  10 any later version.
  11
  12 GNU Classpath is distributed in the hope that it will be useful, but
  13 WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15 General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GNU Classpath; see the file COPYING.  If not, write to the
  19 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  20 02111-1307 USA.
  21
  22 Linking this library statically or dynamically with other modules is
  23 making a combined work based on this library.  Thus, the terms and
  24 conditions of the GNU General Public License cover the whole
  25 combination.
  26
  27 As a special exception, the copyright holders of this library give you
  28 permission to link this library with independent modules to produce an
  29 executable, regardless of the license terms of these independent
  30 modules, and to copy and distribute the resulting executable under
  31 terms of your choice, provided that you also meet, for each linked
  32 independent module, the terms and conditions of the license of that
  33 module.  An independent module is a module which is not derived from
  34 or based on this library.  If you modify this library, you may extend
  35 this exception to your version of the library, but you are not
  36 obligated to do so.  If you do not wish to do so, delete this
  37 exception statement from your version. */
  38
  39
  40 package java.io;
  41
  42 import gnu.java.nio.channels.FileChannelImpl;
  43
  44 import java.nio.channels.ByteChannel;
  45 import java.nio.channels.FileChannel;
  46
  47 /**
  48  * This class represents an opaque file handle as a Java class.  It should
  49  * be used only to pass to other methods that expect an object of this
  50  * type.  No system specific information can be obtained from this object.
  51  *
  52  * @author Aaron M. Renn (arenn@urbanophile.com)
  53  * @author Tom Tromey (tromey@cygnus.com)
  54  * @date September 24, 1998
  55  */
  56 public final class FileDescriptor
  57 {
  58   /**
  59    * A <code>FileDescriptor</code> representing the system standard input
  60    * stream.  This will usually be accessed through the
  61    * <code>System.in</code>variable.
  62    */
  63   public static final FileDescriptor in
  64   = new FileDescriptor (FileChannelImpl.in);
  65
  66   /**
  67    * A <code>FileDescriptor</code> representing the system standard output
  68    * stream.  This will usually be accessed through the
  69    * <code>System.out</code>variable.
  70    */
  71   public static final FileDescriptor out
  72   = new FileDescriptor (FileChannelImpl.out);
  73
  74   /**
  75    * A <code>FileDescriptor</code> representing the system standard error
  76    * stream.  This will usually be accessed through the
  77    * <code>System.err</code>variable.
  78    */
  79   public static final FileDescriptor err
  80   = new FileDescriptor (FileChannelImpl.err);
  81
  82   final ByteChannel channel;
  83
  84   /**
  85    * This method is used to initialize an invalid FileDescriptor object.
  86    */
  87   public FileDescriptor()
  88   {
  89     channel = null;
  90   }
  91
  92   /**
  93    * This method is used to initialize a FileDescriptor object.
  94    */
  95   FileDescriptor(ByteChannel channel)
  96   {
  97     this.channel = channel;
  98   }
  99
 100
 101   /**
 102    * This method forces all data that has not yet been physically written to
 103    * the underlying storage medium associated with this
 104    * <code>FileDescriptor</code>
 105    * to be written out.  This method will not return until all data has
 106    * been fully written to the underlying device.  If the device does not
 107    * support this functionality or if an error occurs, then an exception
 108    * will be thrown.
 109    */
 110   public void sync () throws SyncFailedException
 111   {
 112     if (channel instanceof FileChannel)
 113       {
 114         try
 115           {
 116             ((FileChannel) channel).force(true);
 117           }
 118         catch (IOException ex)
 119           {
 120             if (ex instanceof SyncFailedException)
 121               throw (SyncFailedException) ex;
 122             else
 123               throw new SyncFailedException(ex.toString());
 124           }
 125       }
 126   }
 127
 128   /**
 129    * This methods tests whether or not this object represents a valid open
 130    * native file handle.
 131    *
 132    * @return <code>true</code> if this object represents a valid
 133    * native file handle, <code>false</code> otherwise
 134    */
 135   public boolean valid ()
 136   {
 137     return channel != null && channel.isOpen();
 138   }
 139 }