例11-8.txt

这是一本java基础教程 对新手上路有很大帮助

1）广播数据报的主机
BroadCast.java
import java.net.*;
public class BroadCast extends Thread{
    String s="中国奥运代表团已经获得58枚金牌"; 
    int port=5858;                                  //组播的端口
    InetAddress group=null;                          //组播组
    MulticastSocket socket=null;                      //多点广播套接字 
    BroadCast(){
        try{  group=InetAddress.getByName("239.255.8.0");  //设置组播组为239.255.8.0
             socket=new MulticastSocket(port);   //多点广播套接字将在port端口广播
             socket.setTimeToLive(0);          //多点广播套接字发送数据报范围为本地网络
             socket.joinGroup(group);          
//加入组播组,加入group后，socket发送的数据报可以被加入到group中的成员接收到
        }
        catch(Exception e){}
    }
    public void run(){
        while(true){
           try{  DatagramPacket packet=null;               //待广播的数据报
                byte data[]=s.getBytes(); 
                packet=new DatagramPacket(data,data.length,group,port); 
                System.out.println(new String(data)); 
                socket.send(packet);                     //广播数据报
                sleep(2000);
           }
           catch(Exception e){}
        }
    }
    public static void main(String args[]){
        new BroadCast().start();
    }
}
2）接收数据报的主机
Receive.java 
import java.net.*;
import java.awt.*; 
import java.awt.event.*;
import javax.swing.*;
public class Receive extends JFrame implements Runnable,ActionListener{
    int port;                                      //组播的端口
    InetAddress group=null;                         //组播组的地址
    MulticastSocket socket=null;                     //多点广播套接字
    JButton startReceive,stopReceive;   
    JTextArea showArea;  
    Thread thread;                                 //负责接收信息的线程
    boolean stop=false;
    public Receive(){
       super("定时接收信息");
       thread=new Thread(this);
       startReceive=new JButton("开始接收");
       stopReceive=new JButton("停止接收");
       startReceive.addActionListener(this); 
       stopReceive.addActionListener(this); 
       showArea=new JTextArea(10,10);
       JPanel north=new JPanel();
       north.add(startReceive);
       north.add(stopReceive);
       Container con=getContentPane();
       con.add(north,BorderLayout.NORTH);
       con.add(new JScrollPane(showArea),BorderLayout.CENTER);
       port=5858;                                     
       try{   group=InetAddress.getByName("239.255.8.0"); 
             socket=new MulticastSocket(port);        
             socket.joinGroup(group);       
       }
       catch(Exception e){} 
       setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
       setSize(320,300);
       validate();
       setVisible(true);   
    }
    public void actionPerformed(ActionEvent e){
       if(e.getSource()==startReceive){
          if(!(thread.isAlive())){
              thread=new Thread(this);
              stop=false;
          }
          try{ thread.start(); 
          }
          catch(Exception ee){}
       }
       if(e.getSource()==stopReceive){
          stop=true; 
       }
    }
    public void run(){
       while(true){
          byte data[]=new byte[8192];
          DatagramPacket packet=null;
          packet=new DatagramPacket(data,data.length,group,port); 
          try {  socket.receive(packet);
               String message=new String(packet.getData(),0,packet.getLength());
               showArea.append("\n"+message);
               showArea.setCaretPosition(showArea.getText().length());
          }
          catch(Exception e){}
          if(stop==true)
             break;
       } 
    }
    public static void main(String args[]){
       new Receive();
    }
}