001/* FileDescriptor.java -- Opaque file handle class
002   Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004
003   Free Software Foundation, Inc.
004
005This file is part of GNU Classpath.
006
007GNU Classpath is free software; you can redistribute it and/or modify
008it under the terms of the GNU General Public License as published by
009the Free Software Foundation; either version 2, or (at your option)
010any later version.
011 
012GNU Classpath is distributed in the hope that it will be useful, but
013WITHOUT ANY WARRANTY; without even the implied warranty of
014MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
015General Public License for more details.
016
017You should have received a copy of the GNU General Public License
018along with GNU Classpath; see the file COPYING.  If not, write to the
019Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02002110-1301 USA.
021
022Linking this library statically or dynamically with other modules is
023making a combined work based on this library.  Thus, the terms and
024conditions of the GNU General Public License cover the whole
025combination.
026
027As a special exception, the copyright holders of this library give you
028permission to link this library with independent modules to produce an
029executable, regardless of the license terms of these independent
030modules, and to copy and distribute the resulting executable under
031terms of your choice, provided that you also meet, for each linked
032independent module, the terms and conditions of the license of that
033module.  An independent module is a module which is not derived from
034or based on this library.  If you modify this library, you may extend
035this exception to your version of the library, but you are not
036obligated to do so.  If you do not wish to do so, delete this
037exception statement from your version. */
038
039
040package java.io;
041
042import gnu.java.nio.channels.FileChannelImpl;
043
044import java.nio.channels.ByteChannel;
045import 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 */
056public 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}