multicastdiscovery.java

java2高级教程大学教程的配套光盘源码

// MulticastDiscovery.java
// MulticastDiscovery is an application that demonstrates Jini
// lookup service discovery using multicast.
package com.deitel.advjhtp1.jini.discovery;

// Java core packages
import java.rmi.*;
import java.io.*;
import java.awt.*;
import java.awt.event.*;

// Java extension packages
import javax.swing.*;

// Jini core packages
import net.jini.core.lookup.ServiceRegistrar;

// Jini extension packages
import net.jini.discovery.*;

public class MulticastDiscovery extends JFrame 
   implements DiscoveryListener {
      
   // number of lookup services discovered through multicast
   private int servicesFound = 0;

   private JTextArea outputArea = new JTextArea( 10, 20 );
   
   // MulticastDiscovery constructor
   public MulticastDiscovery ()
   {
      super( "MulticastDiscovery" );

      // discover lookup services in public group using multicast
      try {
         LookupDiscovery lookupDiscovery = new LookupDiscovery( 
            new String[] { "" } );
            
         outputArea.append( "Finding lookup services for " +
            "public group ...\n" );
         
         // listen for DiscoveryEvents
         lookupDiscovery.addDiscoveryListener ( this );
      }

      // handle exception discovering lookup services
      catch ( IOException exception ) {
         exception.printStackTrace();
      }
      
      getContentPane().add( new JScrollPane( outputArea ), 
         BorderLayout.CENTER );      
   }

   // receive notification of found lookup services
   public void discovered ( DiscoveryEvent event )
   {   
      // get the ServiceRegistrars for found lookup services
      ServiceRegistrar[] registrars = event.getRegistrars();
      int order = 0;

      // get the information for each lookup service found
      for ( int i = 0; i < registrars.length ; i++ ) {
         ServiceRegistrar registrar = registrars[ i ];

         if ( registrar != null ) {

            // append information about discovered services
            // to outputArea
            try {
               order = servicesFound + i + 1;
               
               // get the hostname and port number
               Runnable appender = new TextAppender(
                  "Lookup Service " + order + ":\n" +
                  "  Host: " + 
                  registrar.getLocator().getHost() + "\n" +
                  "\n  Port: " + 
                  registrar.getLocator().getPort() + "\n" +
                  "  Group support: " );
               
               // append to outputArea on event-dispatch thread
               SwingUtilities.invokeLater( appender );

               // get the group(s) the lookup service served
               String[] groups = registrar.getGroups();

               StringBuffer names = new StringBuffer();
               
               // get the group names, if empty write public
               for ( int j = 0; j < groups.length ; j++ ) {
                  
                  if ( groups[ j ].equals( "" ) )
                     names.append( "public\t" );
                  else
                     names.append( groups[ j ] + "\t" );
               }
               
               // append group names to outputArea
               SwingUtilities.invokeLater( 
                  new TextAppender( names + "\n" ) );
            }

            // handle exception communicating with ServiceRegistrar
            catch ( RemoteException exception ) {
               exception.printStackTrace();
            }
         }
      }
      
      // update number of services found
      servicesFound = order;
   
   } // end method discovered

   // receive notification of discarded lookup services that
   // are no longer valid
   public void discarded( DiscoveryEvent event ) 
   {
      ServiceRegistrar[] discardedRegistrars = 
         event.getRegistrars();
      
      SwingUtilities.invokeLater( 
         new TextAppender( "Number of discarded registrars: "  +
            discardedRegistrars.length + "\n" ) );
   }
   
   // TextAppender is a Runnable class for appending
   // text to outputArea on the event-dispatching thread.
   private class TextAppender implements Runnable {
      
      private String textToAppend; // text to append to outputArea
      
      // TextAppender constructor
      public TextAppender( String text )
      {
         textToAppend = text;
      }
      
      // append text to outputArea and scroll to bottom
      public void run()
      {
         outputArea.append( textToAppend );
         outputArea.setCaretPosition( 
            outputArea.getText().length() );
      }
      
   } // end inner class TextAppender

   // launch MulticastDiscovery application
   public static void main( String args[] ) 
   {
      // set SecurityManager
      if ( System.getSecurityManager() == null )
         System.setSecurityManager(
            new RMISecurityManager() );

      MulticastDiscovery discovery = new MulticastDiscovery();
      discovery.setDefaultCloseOperation( EXIT_ON_CLOSE );
      discovery.pack();
      discovery.setVisible( true );
   }
}

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