JAVA基于UDP的多点广播数据报技术的一个实现例子

This is a UDP network program. The following presents a multicast datagram program, which is actually a new technology.

package com.han;
import java.net.*;
/**
 * This is a UDP network program.
 * The following presents a multicast datagram program,
 * which is actually a new technology.
 * 
 * @author HAN
 *
 */
public class Weather extends Thread{
	String weather ="节目预告： 八点有大型晚会，请收听";
	int port =9898;
	InetAddress iaddress;//没法初始化，这里只能声明。因为初始化new对象时要抛出异常所以在成员变量区域是语法通不过的。
	MulticastSocket socket;
	//在构造方法中初始化成员变量
	Weather(){
		try {
			//A multicast group is specified by a class D IP address 
			//and by a standard UDP port number.
			//Class D IP addresses are in the range 224.0.0.0 to 239.255.255.255, inclusive.
			//The address 224.0.0.0 is reserved and should not be used.
			iaddress=InetAddress.getByName("233.0.0.0");
			socket=new MulticastSocket(port);
			socket.setTimeToLive(1);
			socket.joinGroup(iaddress);
		}catch(Exception e){
			e.printStackTrace();
		}

	}
	@Override   //最简单的方法也就是建立一个线程来运行
	public void run(){
		while(true){
			byte[] data=weather.getBytes();
			DatagramPacket packet=new DatagramPacket(data,data.length,iaddress,port);
			//			System.out.println(weather);
			System.out.println(new String(data));
			try {
				socket.send(packet);
				sleep(3000);//线程休眠3秒
			} catch (Exception e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}
	public static void main(String[] args){
		Weather w=new Weather();
		w.start();
	}
}

This is the receive part.

package com.han;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.event.*;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
/**
 * This is the receive part.
 * @author HAN
 *
 */
public class Receive extends JFrame implements Runnable, ActionListener{
	private static final long serialVersionUID = 3362377947503474102L;
	int port=9898;
	InetAddress group;
	MulticastSocket socket; //socket sends and receives the packet.
	DatagramPacket packet;
	JButton ince=new JButton("开始接收");
	JButton stop=new JButton("停止接收");
	JTextArea inceAr=new JTextArea(10,20);
	JTextArea inced=new JTextArea(10,20);
	Thread thread;
	boolean b = false;
	byte[] buf=new byte[30];// If the message is longer than the packet's length, the message is truncated.
	
	//在构造方法中设置具体参数特性，也就是初始化
	public Receive(){
		super("广播数据报");
		thread=new Thread(this);
		ince.addActionListener(this);
		stop.addActionListener(this);
		inceAr.setForeground(Color.blue);
		JPanel north=new JPanel();
		north.add(ince);
		north.add(stop);
		add(north,BorderLayout.NORTH);
		JPanel center=new JPanel();
		JScrollPane sp=new JScrollPane(inceAr);
		JScrollPane sp2=new JScrollPane(inced);
		inceAr.setLineWrap(true);
		inceAr.setEditable(false);
		inced.setLineWrap(true);
		inced.setEditable(false);
		center.add(sp);
		center.add(sp2);
		add(center,BorderLayout.CENTER);
		pack(); //JFrame inherited from Window
		validate();
		setVisible(true);
		setDefaultCloseOperation(EXIT_ON_CLOSE);
		try {
			socket=new MulticastSocket(port);
			//A multicast group is specified by a class D IP address 
			//and by a standard UDP port number.
			//Class D IP addresses are in the range 224.0.0.0 to 239.255.255.255, inclusive.
			//The address 224.0.0.0 is reserved and should not be used.
			group=InetAddress.getByName("233.0.0.0");
			socket.joinGroup(group); 
			packet=new DatagramPacket(buf,buf.length);
			
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}
	@Override
	public void run(){
		while(true){
			try {
				socket.receive(packet);
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
//			String message=new String(buf);
			String message=new String(packet.getData(),0,packet.getLength());//very important !!
//			System.out.println(message.length());
			inceAr.setText("正在接受的内容： \n"+message);
			inced.append(message+"\n");
			if(b==true){
				break;
			}
		}
	}
	public void actionPerformed(ActionEvent e){
		Object object=e.getSource();
		if(object==ince){
			//If this thread is already on the state "run", do nothing.
			if(!thread.isAlive()){
				thread=new Thread(this);
				thread.start();
				ince.setBackground(Color.red);
				stop.setBackground(Color.yellow);
				b=false;
			}	
		}
		if(object==stop){
			ince.setBackground(Color.yellow);
			stop.setBackground(Color.red);
			b=true;
		}
	}
	public static void main(String[] args){
		@SuppressWarnings("unused")
		Receive rec=new Receive();
//		rec.setSize(460, 200);//提供了额外设置窗体大小的方式
	}
}

这上面的程序运用了很多JAVA的核心技术以及很多需要注意的地方，可以堪称一个JAVA的精髓例子，记录下来以便以后查阅。