MulticastMessageHandler


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55  package org.lateralnz.messaging.multicast;
56  
57  import java.io.Serializable  ;
58  
59  import java.net.MulticastSocket  ;
60  
61  import org.apache.log4j.Logger;
62  
63  import org.lateralnz.common.util.Constants;
64  import org.lateralnz.common.wrapper.IntHolder;
65  import org.lateralnz.messaging.broadcast.BroadcastMessageHandler;
66  import org.lateralnz.messaging.MessageHandler;
67  
68  /**
69   * a messaging service that uses IP multicast to transmit messages
70   *
71   * @author J R Briggs
72   */
73  public class MulticastMessageHandler extends BroadcastMessageHandler implements MessageHandler, Constants, Serializable   {
74    private static final Logger log       = Logger.getLogger(MulticastMessageHandler.class.getName());
75    private static final int HEADER_SIZE  = 12;  // size of the head (ID[3], MAX[3], ORDER[3])
76    private static final int SPACER_SIZE  = 20;  // a spacer (just in case)
77    
78    private boolean running  = true;
79      
80    private int maxbuf;                            // calculated max buffer size
81    private int receiveBufSize;                    // the receive buffer size for the socket
82    private IntHolder msgID = new IntHolder(0); // ID number to use with fragmented packets
83     
84    protected MulticastMessageHandler(String   ipaddress, int port) throws Exception   {
85      super(ipaddress, port, new MulticastSocket  (port), false);
86  
87      MulticastSocket   ms = (MulticastSocket  )sock;
88      ms.joinGroup(addr);
89      ms.setTimeToLive(32);
90      // we don't want to receive local messages
91      ms.setLoopbackMode(true);
92      
93      listenerThread.start();    
94    }
95  }
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