java DatagramSocket 接收数据 Multicast Socket 发送数据

Question

任何人都可以在java中向我展示一个示例来从DatagramSocket接收数据并通过多播套接字发送相同的数据

Answer 1

Sending multicast datagrams

In order to send any kind of datagram in Java, be it unicast, broadcast or multicast, one needs a java.net.DatagramSocket :

DatagramSocket socket = new DatagramSocket();

One can optionally supply a local port to the DatagramSocket constructor to which the socket must bind. This is only necessary if one needs other parties to be able to reach us at a specific port. A third constructor takes the local port AND the local IP address to which to bind. This is used (rarely) with multi-homed hosts where it is important on which network adapter the traffic is received.

 DatagramSocket socket = new DatagramSocket();

byte[] b = new byte[DGRAM_LENGTH];
DatagramPacket dgram;

dgram = new DatagramPacket(b, b.length,
  InetAddress.getByName(MCAST_ADDR), DEST_PORT);

System.err.println("Sending " + b.length + " bytes to " +
  dgram.getAddress() + ':' + dgram.getPort());
while(true) {
  System.err.print(".");
  socket.send(dgram);
  Thread.sleep(1000);
}

Receiving multicast datagrams

One can use a normal DatagramSocket to send and receive unicast and broadcast datagrams and to send multicast datagrams. In order to receive multicast datagrams, however, one needs a MulticastSocket. The reason for this is simple, additional work needs to be done to control and receive multicast traffic by all the protocol layers below UDP.

byte[] b = new byte[BUFFER_LENGTH];
DatagramPacket dgram = new DatagramPacket(b, b.length);
MulticastSocket socket =
  new MulticastSocket(DEST_PORT); // must bind receive side
socket.joinGroup(InetAddress.getByName(MCAST_ADDR));

while(true) {
  socket.receive(dgram); // blocks until a datagram is received
  System.err.println("Received " + dgram.getLength() +
    " bytes from " + dgram.getAddress());
  dgram.setLength(b.length); // must reset length field!
}

For more Information:

• MulticastSocket
• DatagramSocket

Answer 2

You've got that back to front. You receive multicasts through a MulticastSocket , but you don't need to send them that way: you can send them via a DatagramSocket .

See the Java Tutorial, Custom Networking trail .