001    /* SelectorProvider.java
002       Copyright (C) 2002, 2003, 2004  Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    package java.nio.channels.spi;
039    
040    import gnu.java.nio.SelectorProviderImpl;
041    
042    import java.io.IOException;
043    import java.nio.channels.Channel;
044    import java.nio.channels.DatagramChannel;
045    import java.nio.channels.Pipe;
046    import java.nio.channels.ServerSocketChannel;
047    import java.nio.channels.SocketChannel;
048    
049    
050    /**
051     * @author Michael Koch
052     * @since 1.4
053     */
054    public abstract class SelectorProvider
055    {
056      private static SelectorProvider systemDefaultProvider;
057    
058      /**
059       * Initializes the selector provider.
060       *
061       * @exception SecurityException If a security manager has been installed and
062       * it denies @see RuntimePermission ("selectorProvider").
063       */
064      protected SelectorProvider()
065      {
066        SecurityManager sm = System.getSecurityManager();
067        if (sm != null)
068          sm.checkPermission(new RuntimePermission("selectorProvider"));
069      }
070    
071      /**
072       * Opens a datagram channel.
073       *
074       * @return a new datagram channel object
075       * 
076       * @exception IOException if an error occurs
077       */
078      public abstract DatagramChannel openDatagramChannel()
079        throws IOException;
080    
081      /**
082       * Opens a pipe.
083       *
084       * @return a new pipe object
085       * 
086       * @exception IOException if an error occurs
087       */
088      public abstract Pipe openPipe() throws IOException;
089    
090      /**
091       * Opens a selector.
092       *
093       * @return a new selector object
094       * 
095       * @exception IOException if an error occurs
096       */
097      public abstract AbstractSelector openSelector() throws IOException;
098    
099      /**
100       * Opens a server socket channel.
101       *
102       * @return a new server socket channel object
103       * 
104       * @exception IOException if an error occurs
105       */
106      public abstract ServerSocketChannel openServerSocketChannel()
107        throws IOException;
108    
109      /**
110       * Opens a socket channel.
111       *
112       * @return a new socket channel object
113       * 
114       * @exception IOException if an error occurs
115       */
116      public abstract SocketChannel openSocketChannel() throws IOException;
117    
118      /**
119       * Returns the inherited channel of the VM.
120       *
121       * @return the inherited channel of the VM
122       *
123       * @throws IOException If an I/O error occurs
124       * @throws SecurityException If an installed security manager denies access
125       *         to RuntimePermission("inheritedChannel")
126       *
127       * @since 1.5
128       */
129      public Channel inheritedChannel()
130        throws IOException
131      {
132        SecurityManager sm = System.getSecurityManager();
133        if (sm != null)
134          {
135            sm.checkPermission(new RuntimePermission("inheritedChannel"));
136          }
137        // Implementation note: The default implementation can't do much more
138        // than return null. If a VM can provide something more useful it should
139        // install its own SelectorProvider (maybe a subclass of this one) to
140        // return something more useful.
141        return null;
142      }
143    
144      /**
145       * Returns the system-wide default selector provider for this invocation
146       * of the Java virtual machine.
147       *
148       * @return the default seletor provider
149       */
150      public static synchronized SelectorProvider provider()
151      {
152        if (systemDefaultProvider == null)
153          {
154            String propertyValue =
155              System.getProperty("java.nio.channels.spi.SelectorProvider");
156    
157            if (propertyValue == null || propertyValue.equals(""))
158              systemDefaultProvider = new SelectorProviderImpl();
159            else
160              {
161                try
162                  {
163                    systemDefaultProvider =
164                      (SelectorProvider) Class.forName(propertyValue)
165                                              .newInstance();
166                  }
167                catch (Exception e)
168                  {
169                    System.err.println("Could not instantiate class: "
170                                       + propertyValue);
171                    systemDefaultProvider = new SelectorProviderImpl();
172                  }
173              }
174          }
175    
176        return systemDefaultProvider;
177      }
178    }