JAVA基礎知識之網絡編程——-使用MutilcastSocket實現多點廣播

IP多點廣播原理

設置一組特殊網絡地址作為多點廣播地址，每一個多點廣播地址都被看作一個組，當客戶需要發送和接受信息時，加入到該組即可。

IP協議為多點廣播提供了一批特殊的IP地址，范圍是224.0.0.0 ~ 239.255.255.255

JAVA中使用MutilcastSocket加入一個廣播組(joinGroup)，從而在組內發送和接受數據報DatagramPacket。

MutilcastSocket比起普通的UDP通信的DatagramSocket多了setTimeToLive(int ttl)，參數ttl決定廣播組的范圍，默認為1，表示局域網。

下面是一個簡單例子，BroadcastSocket中用一個線程接收鍵盤輸入（因為會阻塞）並使用MutilcastSocket發送數據，

用另一個線程從MutilcastSocket讀取數據並打印出來，

package udp;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket;
import java.util.Scanner;

public class BroadcastSocket implements Runnable{
    private static final String BROADCAST_IP = "230.0.0.1";
    public static final int BROADCAST_PORT = 3000;
    private static final int DATA_LEN = 4096;
    private MulticastSocket socket = null;
    private InetAddress broadcastAddress = null;
    //用來接收鍵盤輸入
    private Scanner scan = null;
    //用來接收網絡字節
    byte[] inBuff = new byte[DATA_LEN];
    //用將inBuff封裝進DatagramPacket
    private DatagramPacket inPacket = new DatagramPacket(inBuff, inBuff.length);
    //封裝發送數據的DatagramPacket
    private DatagramPacket outPacket = null;
    public void init() throws IOException {
        try {
            Scanner scan = new Scanner(System.in);
            socket = new MulticastSocket(BROADCAST_PORT);
            broadcastAddress = InetAddress.getByName(BROADCAST_IP);
            socket.joinGroup(broadcastAddress);
            //設置本是否阻止MulticastSocket會發送給自身, true表示阻止 
            socket.setLoopbackMode(false);
            //初始化outPacket
            outPacket = new DatagramPacket(new byte[0], 0 , broadcastAddress, BROADCAST_PORT);
            new Thread(this).start();
            //讀取鍵盤輸入
            while (scan.hasNextLine()) {
                //需要先將鍵盤輸入轉為byte字節才能設置DatagramPacket的值
                byte[] buff = scan.nextLine().getBytes();
                outPacket.setData(buff);
                socket.send(outPacket);
            }
        } finally {
            socket.close();
        }
    }
    @Override
    public void run() {
        try {
            while (true) {
                socket.receive(inPacket);
                System.out.println("聊天信息："+new String(inBuff, 0, inPacket.getLength()));
            }
        } //捕獲異常
        catch (IOException ex) {
            ex.printStackTrace();
            try {
                if (socket != null) {
                    socket.leaveGroup(broadcastAddress);
                    socket.close();
                }
                System.exit(1);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        
    }
    
    public static void main(String[] args) throws IOException {
        new BroadcastSocket().init();
    }
}

執行結果如下，