001 /* FileDescriptor.java -- Opaque file handle class
002 Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004
003 Free Software Foundation, Inc.
004
005 This file is part of GNU Classpath.
006
007 GNU Classpath is free software; you can redistribute it and/or modify
008 it under the terms of the GNU General Public License as published by
009 the Free Software Foundation; either version 2, or (at your option)
010 any later version.
011
012 GNU Classpath is distributed in the hope that it will be useful, but
013 WITHOUT ANY WARRANTY; without even the implied warranty of
014 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
015 General Public License for more details.
016
017 You should have received a copy of the GNU General Public License
018 along with GNU Classpath; see the file COPYING. If not, write to the
019 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
020 02110-1301 USA.
021
022 Linking this library statically or dynamically with other modules is
023 making a combined work based on this library. Thus, the terms and
024 conditions of the GNU General Public License cover the whole
025 combination.
026
027 As a special exception, the copyright holders of this library give you
028 permission to link this library with independent modules to produce an
029 executable, regardless of the license terms of these independent
030 modules, and to copy and distribute the resulting executable under
031 terms of your choice, provided that you also meet, for each linked
032 independent module, the terms and conditions of the license of that
033 module. An independent module is a module which is not derived from
034 or based on this library. If you modify this library, you may extend
035 this exception to your version of the library, but you are not
036 obligated to do so. If you do not wish to do so, delete this
037 exception statement from your version. */
038
039
040 package java.io;
041
042 import gnu.java.nio.channels.FileChannelImpl;
043
044 import java.nio.channels.ByteChannel;
045 import java.nio.channels.FileChannel;
046
047 /**
048 * This class represents an opaque file handle as a Java class. It should
049 * be used only to pass to other methods that expect an object of this
050 * type. No system specific information can be obtained from this object.
051 *
052 * @author Aaron M. Renn (arenn@urbanophile.com)
053 * @author Tom Tromey (tromey@cygnus.com)
054 * @date September 24, 1998
055 */
056 public final class FileDescriptor
057 {
058 /**
059 * A <code>FileDescriptor</code> representing the system standard input
060 * stream. This will usually be accessed through the
061 * <code>System.in</code>variable.
062 */
063 public static final FileDescriptor in
064 = new FileDescriptor (FileChannelImpl.in);
065
066 /**
067 * A <code>FileDescriptor</code> representing the system standard output
068 * stream. This will usually be accessed through the
069 * <code>System.out</code>variable.
070 */
071 public static final FileDescriptor out
072 = new FileDescriptor (FileChannelImpl.out);
073
074 /**
075 * A <code>FileDescriptor</code> representing the system standard error
076 * stream. This will usually be accessed through the
077 * <code>System.err</code>variable.
078 */
079 public static final FileDescriptor err
080 = new FileDescriptor (FileChannelImpl.err);
081
082 final ByteChannel channel;
083
084 /**
085 * This method is used to initialize an invalid FileDescriptor object.
086 */
087 public FileDescriptor()
088 {
089 channel = null;
090 }
091
092 /**
093 * This method is used to initialize a FileDescriptor object.
094 */
095 FileDescriptor(ByteChannel channel)
096 {
097 this.channel = channel;
098 }
099
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 }