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：

[java]
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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：

[java]
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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：

[java]
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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：

[java]
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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();
}

}

如有疑问请留言。未完待续。。。

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