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., 51 Franklin Street, Fifth Floor, Boston, MA
20 02110-1301 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    */
FileDescriptor()87   public FileDescriptor()
88   {
89     channel = null;
90   }
91 
92   /**
93    * This method is used to initialize a FileDescriptor object.
94    */
FileDescriptor(ByteChannel channel)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    */
sync()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    */
valid()135   public boolean valid ()
136   {
137     return channel != null && channel.isOpen();
138   }
139 }
140