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    }