使用DatagramSocke和DatagramPacket实现简单的聊天室功能，具体如下：

• 使用DatagramSocke打开端口用来接收和发送数据
• 使用DatagramPacket对数据进行打包
• 实现Runnable接口启动一个接收线程和一个发送线程
• 使用UDP协议进行通讯

UDP协议通讯类似于发短信功能，无需握手连接，实现较为简单。

发送线程

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.*;

public class UdpSend implements Runnable{
    DatagramSocket socket = null;
    BufferedReader reader = null;
    private int fromPort;
    private String toIP;
    private int toPort;

    public UdpSend(int fromPort, String toIP, int toPort) throws Exception {
        this.fromPort = fromPort;
        this.toIP = toIP;
        this.toPort = toPort;

        socket = new DatagramSocket(fromPort);
        reader = new BufferedReader(new InputStreamReader(System.in));
    }

    @Override
    public void run() {
        while(true) {
            try {
                //读取控制台数据
                String data = reader.readLine();
                byte[] datas = data.getBytes();
                //创建包
                DatagramPacket packet = new DatagramPacket(datas, 0, datas.length, new InetSocketAddress(this.toIP, this.toPort));
                //发送包
                socket.send(packet);
                if(data.equals("bye")){//取消发送条件
                    break;
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }socket.close();
    }
}

接收线程

public class UdpReceive implements Runnable {
    DatagramSocket socket = null;
    private int ownPort;
    private String msgFrom;

    public UdpReceive(int ownPort, String msgFrom) throws Exception {
        this.ownPort = ownPort;
        this.msgFrom = msgFrom;
        socket = new DatagramSocket(ownPort);
    }
    @Override
    public void run() {
        while (true) {
            try {
                //接受数据包
                byte[] buffer = new byte[1024];
                DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
                socket.receive(packet);//阻塞接收
                byte[] data = packet.getData();
                int len = packet.getLength();

                String receiveData = new String(data, 0, len);
                System.out.println(msgFrom+":"+receiveData);
                if (receiveData.equals("bye")) {
                    break;
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        socket.close();
    }
}

学生端

public class student {
    public static void main(String[] args) throws Exception {
        new Thread(new UdpReceive(7777,"老师")).start();
        new Thread(new UdpSend(8888,"localhost",9090)).start();
    }
}

老师端

public class teacher {
    public static void main(String[] args) throws Exception {
        new Thread(new UdpReceive(9090,"学生")).start();
        new Thread(new UdpSend(9999,"localhost",7777)).start();
    }
}

遇到的Bug

在控制台显示数据包时，数据后面会跟许多空格：

经查找原因，发现是由于收到数据包转换为String类型时数据长度设置错误：

//错误示范

byte[] buffer = new byte[1024];
DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
socket.receive(packet);//阻塞接收

byte[] data = packet.getData();//获取数据包中的数据
String receiveData = new String(data, 0, data.length);//此处数据长度不可使用数组的长度


System.out.println(msgFrom+":"+receiveData);

//正确代码

byte[] buffer = new byte[1024];
DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
socket.receive(packet);//阻塞接收

byte[] data = packet.getData();
int len = packet.getLength();//使用DatagramPacket的getLength()方法获取数据的长度。
String receiveData = new String(data, 0, len);//使用正确的长度参数即可避免错误。

System.out.println(msgFrom+":"+receiveData);

Java网络编程：使用DatagramSocket实现简单聊天功能