单播（Unicast）

单播是最常见的通信方式，数据从一个发送方传输到一个特定的接收方。发送方将数据包发送到接收方的IP地址和端口号，接收方通过监听指定的端口接收数据。单播适用于一对一的通信场景。

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

public class UDPSender {
    public static void main(String[] args) {
        try {
            DatagramSocket socket = new DatagramSocket();
            String message = "Hello, World!";
            byte[] buffer = message.getBytes();
            InetAddress address = InetAddress.getByName("127.0.0.1");
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length, address, 12345);
            socket.send(packet);
            socket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
 

接收方

import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class UDPReceiver {
    public static void main(String[] args) {
        try {
            DatagramSocket socket = new DatagramSocket(12345);
            byte[] buffer = new byte[1024];
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
            socket.receive(packet);
            String receivedMessage = new String(packet.getData(), 0, packet.getLength());
            System.out.println(receivedMessage);
            socket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
 

广播（Broadcast）

广播是将数据包发送到同一网络中的所有设备。发送方将数据包发送到广播地址（如255.255.255.255），所有在同一网络中的设备都能接收到该数据包。广播适用于一对多的通信场景，但会占用大量网络带宽。

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

public class UDPSender {
    public static void main(String[] args) {
        try {
            DatagramSocket socket = new DatagramSocket();
            socket.setBroadcast(true);

            String message = "Hello, Everyone!";
            byte[] buffer = message.getBytes();

            DatagramPacket packet = new DatagramPacket(buffer, buffer.length, InetAddress.getByName("255.255.255.255"), 12345);
            socket.send(packet);

            socket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
 

接收方代码

import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class UDPReceiver {
    public static void main(String[] args) {
        try {
            DatagramSocket socket = new DatagramSocket(12345);

            byte[] buffer = new byte[1024];
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);

            socket.receive(packet);
            String receivedMessage = new String(packet.getData(), 0, packet.getLength());
            System.out.println(receivedMessage);

            socket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
 

组播（Multicast）

组播是将数据包发送到一组特定的设备。发送方将数据包发送到组播地址（如224.0.0.1），只有加入该组播组的设备才能接收到数据包。组播适用于一对多的通信场景，且比广播更节省网络带宽。

import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket;

public class MulticastSender {
    public static void main(String[] args) {
        try {
            InetAddress group = InetAddress.getByName("224.0.0.1");
            MulticastSocket socket = new MulticastSocket();
            String message = "Hello, Group!";
            DatagramPacket packet = new DatagramPacket(message.getBytes(), message.length(), group, 12345);
            socket.send(packet);
            socket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
 

接收方

import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket;

public class MulticastReceiver {
    public static void main(String[] args) {
        try {
            InetAddress group = InetAddress.getByName("224.0.0.1");
            MulticastSocket socket = new MulticastSocket(12345);
            socket.joinGroup(group);
            byte[] buffer = new byte[1024];
            DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
            socket.receive(packet);
            String received = new String(packet.getData(), 0, packet.getLength());
            System.out.println(received);
            socket.leaveGroup(group);
            socket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}