Java Udp协议三种通讯方式：单播、组播、广播示范代码

单播

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

/**
 * Udp 单播方式示范
 */
public class UdpDemo {
    public static void main(String[] args) {
        new Thread(()->{
            UdpDemoServer server = null;
            try {
                server = new UdpDemoServer("127.0.0.1",5001);
                System.out.println("服务器启动成功,接收数据...");
                byte[] data = server.receive(1024);
                System.out.println("服务器收到数据：");
                System.out.println(new String(data));
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                if (server != null){
                    server.close();
                }
            }
        }).start();

        new Thread(()->{
            UdpDemoClient client = null;
            try {
                Thread.sleep(1500);
                client = new UdpDemoClient("127.0.0.1",5001);
                System.out.println("客户端启动成功");
                client.send("你好，我是客户端");
                System.out.println("客户成功发送数据");
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                if (client != null){
                    client.close();
                }
            }
        }).start();
    }
}
class UdpDemoServer{
    private DatagramSocket socket;
    private InetAddress inetAddress;
    private int port;
    public UdpDemoServer(String ip,int port) throws IOException {
        this.inetAddress = InetAddress.getByName(ip);
        this.port = port;
        this.socket = new DatagramSocket(port);
    }
    public byte[] receive(int length)throws IOException{
        DatagramPacket packet = new DatagramPacket(new byte[length],length);
        this.socket.receive(packet);
        return packet.getData();
    }
    public void close(){
        if (this.socket != null && !this.socket.isClosed()){
            this.socket.close();
        }
    }
}
class UdpDemoClient{
    private DatagramSocket socket;
    private InetAddress inetAddress;
    private int port;
    public UdpDemoClient(String ip,int port) throws IOException {
        this.inetAddress = InetAddress.getByName(ip);
        this.port = port;
        this.socket = new DatagramSocket();
    }
    public void send(String msg)throws IOException{
        byte[] data = msg.getBytes();
        DatagramPacket packet = new DatagramPacket(data,data.length,this.inetAddress,this.port);
        this.socket.send(packet);
    }
    public void close(){
        if (this.socket != null && !this.socket.isClosed()){
            this.socket.close();
        }
    }
}

组播

224.0.0.0～224.0.0.255为预留的组播地址（永久组地址），地址224.0.0.0保留不做分配，其它地址供路由协议使用；
224.0.1.0～224.0.1.255是公用组播地址，可以用于Internet；

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.MulticastSocket;

/**
 * Udp 组播方式示范
 */
public class UdpMulticastDemo {
    public static void main(String[] args) {
        new Thread(()->{
            UdpMulticastServer server = null;
            try {
                server = new UdpMulticastServer("224.0.1.0",5000);
                System.out.println("服务器启动成功,接收数据...");
                byte[] data = server.receive(1024);
                System.out.println("服务器收到数据：");
                System.out.println(new String(data));
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                if (server != null){
                    server.close();
                }
            }
        }).start();

        new Thread(()->{
            UdpMulticastClient client = null;
            try {
                Thread.sleep(1500);
                client = new UdpMulticastClient("224.0.1.0",5000);
                System.out.println("客户端启动成功");
                client.send("你好，我是客户端");
                System.out.println("客户成功发送数据");
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                if (client != null){
                    client.close();
                }
            }
        }).start();
    }
}
class UdpMulticastServer {
    private MulticastSocket multicastSocket;
    private InetAddress inetAddress;
    private int port;
    public UdpMulticastServer(String address, int port) throws IOException {
        inetAddress = InetAddress.getByName(address);
        this.port = port;
        multicastSocket = new MulticastSocket(port);
        multicastSocket.joinGroup(this.inetAddress);
    }
    public byte[] receive(int length) throws IOException {
        DatagramPacket packet = new DatagramPacket(new byte[length],length);
        this.multicastSocket.receive(packet);
        return packet.getData();
    }
    public void close(){
        if (this.multicastSocket != null && !this.multicastSocket.isClosed()){
            this.multicastSocket.close();
        }
    }
}
class UdpMulticastClient {
    private DatagramSocket socket;
    private InetAddress inetAddress;
    private int port;
    public UdpMulticastClient(String address, int port) throws IOException {
        inetAddress = InetAddress.getByName(address);
        this.port = port;
        socket = new MulticastSocket();
    }
    public void send(String msg) throws IOException {
        byte[] data = msg.getBytes();
        DatagramPacket packet = new DatagramPacket(data,data.length,this.inetAddress,port);
        this.socket.send(packet);
    }
    public void close(){
        if (this.socket != null && !this.socket.isClosed()){
            this.socket.close();
        }
    }
}

广播

广播地址 255.255.255.255

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

/**
 * Udp 广播方式示范
 */
public class UdpBroadcastDemo {
    public static void main(String[] args) {
        new Thread(()->{
            UdpBroadcastDemoServer server = null;
            try {
                server = new UdpBroadcastDemoServer("255.255.255.255",5001);
                System.out.println("服务器1启动成功,接收数据...");
                byte[] data = server.receive(1024);
                System.out.println("服务器1收到数据：");
                System.out.println(new String(data));
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                if (server != null){
                    server.close();
                }
            }
        }).start();

        new Thread(()->{
            UdpBroadcastDemoClient client = null;
            try {
                Thread.sleep(1500);
                client = new UdpBroadcastDemoClient("255.255.255.255",5001);
                System.out.println("客户端启动成功");
                client.send("你好，我是客户端");
                System.out.println("客户成功发送数据");
            }catch (Exception e){
                e.printStackTrace();
            }finally {
                if (client != null){
                    client.close();
                }
            }
        }).start();
    }
}

class UdpBroadcastDemoServer{
    private DatagramSocket socket;
    private InetAddress inetAddress;
    private int port;
    public UdpBroadcastDemoServer(String ip,int port) throws IOException {
        this.inetAddress = InetAddress.getByName(ip);
        this.port = port;
        this.socket = new DatagramSocket(port);
    }
    public byte[] receive(int length)throws IOException{
        DatagramPacket packet = new DatagramPacket(new byte[length],length);
        this.socket.receive(packet);
        return packet.getData();
    }
    public void close(){
        if (this.socket != null && !this.socket.isClosed()){
            this.socket.close();
        }
    }
}

class UdpBroadcastDemoClient{
    private DatagramSocket socket;
    private InetAddress inetAddress;
    private int port;
    public UdpBroadcastDemoClient(String ip,int port) throws IOException {
        this.inetAddress = InetAddress.getByName(ip);
        this.port = port;
        this.socket = new DatagramSocket();
    }
    public void send(String msg)throws IOException{
        byte[] data = msg.getBytes();
        DatagramPacket packet = new DatagramPacket(data,data.length,this.inetAddress,this.port);
        this.socket.send(packet);
    }
    public void close(){
        if (this.socket != null && !this.socket.isClosed()){
            this.socket.close();
        }
    }
}