JAVA基础知识之网络编程——-使用MutilcastSocket实现多点广播

IP多点广播原理

设置一组特殊网络地址作为多点广播地址，每一个多点广播地址都被看作一个组，当客户需要发送和接受信息时，加入到该组即可。

IP协议为多点广播提供了一批特殊的IP地址，范围是224.0.0.0 ~ 239.255.255.255

JAVA中使用MutilcastSocket加入一个广播组(joinGroup)，从而在组内发送和接受数据报DatagramPacket。

MutilcastSocket比起普通的UDP通信的DatagramSocket多了setTimeToLive(int ttl)，参数ttl决定广播组的范围，默认为1，表示局域网。

下面是一个简单例子，BroadcastSocket中用一个线程接收键盘输入（因为会阻塞）并使用MutilcastSocket发送数据，

用另一个线程从MutilcastSocket读取数据并打印出来，

1 package udp;
2
3 import java.io.IOException;
4 import java.net.DatagramPacket;
5 import java.net.InetAddress;
6 import java.net.MulticastSocket;
7 import java.util.Scanner;
8
9 public class BroadcastSocket implements Runnable{
10     private static final String BROADCAST_IP = "230.0.0.1";
11     public static final int BROADCAST_PORT = 3000;
12     private static final int DATA_LEN = 4096;
13     private MulticastSocket socket = null;
14     private InetAddress broadcastAddress = null;
15     //用来接收键盘输入
16     private Scanner scan = null;
17     //用来接收网络字节
18     byte[] inBuff = new byte[DATA_LEN];
19     //用将inBuff封装进DatagramPacket
20     private DatagramPacket inPacket = new DatagramPacket(inBuff, inBuff.length);
21     //封装发送数据的DatagramPacket
22     private DatagramPacket outPacket = null;
23     public void init() throws IOException {
24         try {
25             Scanner scan = new Scanner(System.in);
26             socket = new MulticastSocket(BROADCAST_PORT);
27             broadcastAddress = InetAddress.getByName(BROADCAST_IP);
28             socket.joinGroup(broadcastAddress);
29             //设置本是否阻止MulticastSocket会发送给自身, true表示阻止
30             socket.setLoopbackMode(false);
31             //初始化outPacket
32             outPacket = new DatagramPacket(new byte[0], 0 , broadcastAddress, BROADCAST_PORT);
33             new Thread(this).start();
34             //读取键盘输入
35             while (scan.hasNextLine()) {
36                 //需要先将键盘输入转为byte字节才能设置DatagramPacket的值
37                 byte[] buff = scan.nextLine().getBytes();
38                 outPacket.setData(buff);
39                 socket.send(outPacket);
40             }
41         } finally {
42             socket.close();
43         }
44     }
45     @Override
46     public void run() {
47         try {
48             while (true) {
49                 socket.receive(inPacket);
50                 System.out.println("聊天信息："+new String(inBuff, 0, inPacket.getLength()));
51             }
52         } //捕获异常
53         catch (IOException ex) {
54             ex.printStackTrace();
55             try {
56                 if (socket != null) {
57                     socket.leaveGroup(broadcastAddress);
58                     socket.close();
59                 }
60                 System.exit(1);
61             } catch (IOException e) {
62                 e.printStackTrace();
63             }
64         }
65
66     }
67
68     public static void main(String[] args) throws IOException {
69         new BroadcastSocket().init();
70     }
71 }

执行结果如下，