转载关于The JxtaMulticastSocket class-优快云博客

本文介绍JXTA组播套接字(JxtaMulticastSocket)的使用方法，这是一种基于UDP的数据报套接字，用于互联网上的组播主机间通信。通过加入特定的组，可以实现消息发送和接收。文章提供了创建、加入组播组并发送及接收数据的具体示例。

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The JxtaMulticastSocket class is useful for sending and receiving JXTA multicast packets. A JxtaMulticastSocket is a (UDP) DatagramSocket, with additional capabilities for joining "groups" of other multicast hosts on the internet. A multicast group is specified within the context of PeerGroup and a propagate pipe advertisement. One would join a multicast group by first creating a MulticastSocket with the desired peer group and pipe advertisement :

  // join a Multicast group and send the group salutations
  ...
  String msg = "Hello";
  MulticastSocket s = new JxtaMulticastSocket(peergroup, propPipeAdv);
  //We are joined at this point
  DatagramPacket hi = new DatagramPacket(msg.getBytes(), msg.length());
  s.send(hi);
  // get their responses!
  byte[] buf = new byte[1000];
  DatagramPacket recv = new DatagramPacket(buf, buf.length);
  s.receive(recv);
  ...
  // OK, I'm done talking - leave the group...
  s.close();

One can also respond only to the sender of the datagram as follows :

  DatagramPacket res = new DatagramPacket(response.getBytes(), response.length());
  res.setAddress(recv.getAddress());
  s.send(res);

When one sends a message to a multicast group, all subscribing recipients to that peergroup and pipe receive the message (including themselves) When a socket subscribes to a multicast group/port, it receives datagrams sent by other hosts to the group/pipe, as do all other members of the group and pipe. A socket relinquishes membership in a group by the close() method. Multiple MulticastSocket's may subscribe to a multicast group and pipe concurrently, and they will all receive group datagrams. When a datagram is sent it carries along with the peerid of the sender. The PeerID is represented as a InetAddress in the form of host/ipadress where host name is the peerid, and ip address is always represented as 0.0.0.0 since it is meaningless in the context of JXTA. e.g of InetAddress resembles the following:

 uuid-59616261646162614A787461503250339C6014B0F21A49DBBDF2ADBDDBCB314703/0.0.0.0