Java网络编程 MulticastSocket类的使用

// MCClient.java

import java.io.*;
import java.net.*;

class MCClient
{
　public static void main (String [] args) throws IOException
　{
　　// Create a MulticastSocket bound to local port 10000. All
　　// multicast packets from the server program are received
　　// on that port.

　　MulticastSocket s = new MulticastSocket (10000);

　　// Obtain an InetAddress object that contains the multicast
　　// group address 231.0.0.1. The InetAddress object is used by
　　// DatagramPacket.

　　InetAddress group = InetAddress.getByName ("231.0.0.1");

　　// Join the multicast group so that datagram packets can be
　　// received.

　　s.joinGroup (group);

　　// Read several datagram packets from the server program.

　　for (int i = 0; i < 10; i++)
　　{
　　　// No line will exceed 256 bytes.

　　　byte [] buffer = new byte [256];

　　　// The DatagramPacket object needs no addressing
　　　// information because the socket contains the address.

　　　DatagramPacket dgp = new DatagramPacket (buffer,
　　　　　　buffer.length);

　　　// Receive a datagram packet.

　　　s.receive (dgp);

　　　// Create a second byte array with a length that matches
　　　// the length of the sent data.

　　　byte [] buffer2 = new byte [dgp.getLength ()];

　　　// Copy the sent data to the second byte array.

　　　System.arraycopy (dgp.getData (),
　　　　　　　　0,
　　　　　　　　buffer2,
　　　　　　　　0,
　　　　　　　　dgp.getLength ());

　　　// Print the contents of the second byte array. (Try
　　　// printing the contents of buffer. You will soon see why
　　　// buffer2 is used.)

　　　System.out.println (new String (buffer2));
　　}

　　// Leave the multicast group.

　　s.leaveGroup (group);

　　// Close the socket.

　　s.close ();
　}
}

// MCServer.java

import java.io.*;
import java.net.*;

class MCServer
{
　public static void main (String[] args) throws IOException
　{
　　System.out.println ("Server starting...\n"); 

　　// Create a MulticastSocket not bound to any port.

　　MulticastSocket s = new MulticastSocket ();

　　// Because MulticastSocket subclasses DatagramSocket, it is
　　// legal to replace MulticastSocket s = new MulticastSocket ();
　　// with the following line.

　　  // DatagramSocket s = new DatagramSocket ();

　　// Obtain an InetAddress object that contains the multicast
　　// group address 231.0.0.1. The InetAddress object is used by
　　// DatagramPacket.

　　InetAddress group = InetAddress.getByName ("231.0.0.1");

　　// Create a DatagramPacket object that encapsulates a reference
　　// to a byte array (later) and destination address
　　// information. The destination address consists of the
　　// multicast group address (as stored in the InetAddress object)
　　// and port number 10000 -- the port to which multicast datagram
　　// packets are sent. (Note: The dummy array is used to prevent a
　　// NullPointerException object being thrown from the
　　// DatagramPacket constructor.)

　　byte [] dummy = new byte [0];

　　DatagramPacket dgp = new DatagramPacket (dummy,
　　　　0,
　　　　group,
　　　　10000);

　　// Send 30000 Strings to the port.

　　for (int i = 0; i < 30000; i++)
　　{
　　　// Create an array of bytes from a String. The platform's
　　　// default character set is used to convert from Unicode
　　　// characters to bytes.

　　　byte [] buffer = ("Video line " + i).getBytes ();

　　　// Establish the byte array as the datagram packet's
　　　// buffer.

　　　dgp.setData (buffer);

　　　// Establish the byte array's length as the length of the
　　　// datagram packet's buffer.

　　　dgp.setLength (buffer.length);

　　　// Send the datagram to all members of the multicast group
　　　// that listen on port 10000.

　　　s.send (dgp);
　　}

　　// Close the socket.

　　s.close ();
　}
}