java udp 广播

udp 是一种网络通信协议，不需要客户端和服务器端建立连接即可进行通讯功能。相对于Tcp协议它有着tcp用很多优点，例如广播功能。udp的广播功能可以指定特定网段进行广播内容，而无需知道接收者是谁，只有接受者在广播范围内即可接收广播内容。其实基于这个功能可以实现一个局域网群聊室的功能。

udp广播发送有两种形式，

方式一：通过DatagramSocket实现

方式二：通过MulticastSocket 实现

方式一：demo;

1,数据发送端：

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import java.io.IOException;

import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.InetAddress;

import java.net.SocketException;

import java.net.UnknownHostException;

public class SendIP {

public static void main(String args[]) {

new SendIP().lanchApp();

}

private void lanchApp(){

SendThread th=new SendThread();

th.start();

}

private class SendThread extends Thread{

@Override

public void run() {

while(true){

try {

Thread.sleep(1000);

} catch (InterruptedException e) {

e.printStackTrace();

}

try {

BroadcastIP();

} catch (Exception e) {

e.printStackTrace();

}

}

}

private void BroadcastIP()throws Exception{

DatagramSocket dgSocket=new DatagramSocket();

byte b[]="你好，这是我发给你的消息".getBytes();

DatagramPacket dgPacket=new DatagramPacket(b,b.length,InetAddress.getByName("255.255.255.255"),8989);

dgSocket.send(dgPacket);

dgSocket.close();

System.out.println("send message is ok.");

}

}

}

2，数据接收端：

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import java.net.DatagramPacket;

import java.net.DatagramSocket;

import java.net.SocketException;

import java.util.regex.Matcher;

import java.util.regex.Pattern;

public class SearchIP{

public static void main(String args[])throws Exception{

new SearchIP().lanchApp();

}

private void lanchApp(){

receiveThread th=new receiveThread();

th.start();

}

private class receiveThread extends Thread{

@Override

public void run() {

while(true){

try {

Thread.sleep(1000);

} catch (InterruptedException e) {

e.printStackTrace();

}

try {

receiveIP();

} catch (Exception e) {

e.printStackTrace();

}

}

}

private void receiveIP() throws Exception{

DatagramSocket dgSocket=new DatagramSocket(8989);

byte[] by=new byte[1024];

DatagramPacket packet=new DatagramPacket(by,by.length);

dgSocket.receive(packet);

String str=new String(packet.getData(),0,packet.getLength());

System.out.println("接收到数据大小:"+str.length());

System.out.println("接收到的数据为："+str);

dgSocket.close();

System.out.println("recevied message is ok.");

}

}

}

方式二demo;

1,数据发送端：

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import java.io.IOException;

import java.net.DatagramPacket;

import java.net.InetAddress;

import java.net.MulticastSocket;

public class MulBroadcast extends Thread{

String info ="节目预告： 恭喜您中500w彩票了";

int port =9898;

InetAddress address;

MulticastSocket socket;

public MulBroadcast(){

try{

address=InetAddress.getByName("233.0.0.0");

socket=new MulticastSocket(port);

socket.setTimeToLive(1);

socket.joinGroup(address);

}catch(IOException 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=info.getBytes();

DatagramPacket packet=new DatagramPacket(data,data.length,address,port);

try {

socket.send(packet);

Thread.sleep(3000);

} catch (Exception e) {

e.printStackTrace();

}

System.out.println("消息已发送：");

}

}

public static void main(String[] args){

new MulBroadcast().start();

}

}

2，数据接收端：

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import java.io.IOException;

import java.net.DatagramPacket;

import java.net.InetAddress;

import java.net.MulticastSocket;

public class MulReceiverIP extends Thread{

int port=9898;

InetAddress group;

MulticastSocket socket; //socket sends and receives the packet.

DatagramPacket packet;

byte[] buf=new byte[30];// If the message is longer than the packet's length, the message is truncated.

public MulReceiverIP(){

try {

socket=new MulticastSocket(port);

group=InetAddress.getByName("233.0.0.0");

socket.joinGroup(group); //加入广播组,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。

packet=new DatagramPacket(buf,buf.length);

} catch (IOException e) {

e.printStackTrace();

}

}

@Override

public void run(){

while(true){

try {

socket.receive(packet);

} catch (IOException e) {

e.printStackTrace();

}

// String message=new String(buf);

String message=new String(packet.getData(),0,packet.getLength());//very important !!

System.out.println("接受消息内容: "+message);

}

}

public static void main(String[] args) {

new MulReceiverIP().start();

}

}