Java UDP多线程通信的一个问题

Question

我现在正在学习java网络编程，我写了一个程序，客户端将当前时间的30倍发送到服务器，服务器将创建一个新线程来解析接收到的UDP数据包，如果服务器接收到UDP，则反馈给客户端数据包。

问题是，在我运行我的代码后，服务器可以接收 UDP 数据包并创建一个新线程，但似乎 DatagramSocket 和 DatagramPacket 没有传递给线程。因此线程无法反馈给客户端，客户端在发送第一个 UDP 数据包后会一直等待。

我的代码在这里：

服务器

public class MulUDPServer {
public static void main(String[] args) {
    DatagramSocket socket = null; 
    DatagramPacket receivedPacket; 
    final int PORT = 10010; 
    byte[] b = new byte[1024];
    receivedPacket = new DatagramPacket(b, b.length);
    try {
        socket = new DatagramSocket(PORT);
        System.out.println("Server start!");
        while (true) {
            // receive the packet from server
            socket.receive(receivedPacket);
            // to check if Server get the packet
            System.out.println(new String(receivedPacket.getData(), 0, receivedPacket.getLength()));
            // start the thread to handle the packet we have got
            Thread thread = new Thread(new LogicThread(socket, receivedPacket));
            thread.start();
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        try {
            // close the connection
            socket.close();
        } catch (Exception e) {
        }
    }
}

线程

public class LogicThread implements Runnable {

DatagramSocket socket = null;
DatagramPacket receivedPacket = null;

public LogicThread(DatagramSocket socket, DatagramPacket receivedPacket) {
    this.socket = socket;
    this.receivedPacket = receivedPacket;
}

public void run() {
    try {
        // to test if a thread have been set up
        System.out.println("a thread have been set up");
        byte[] data = receivedPacket.getData();
        int len = receivedPacket.getLength();
        // get the client IP
        InetAddress clientAddress = receivedPacket.getAddress();
        // get the client port
        int clientPort = receivedPacket.getPort();
        // print the info about received packet
        System.out.println("Client's IP：" + clientAddress.getHostAddress());
        System.out.println("Client's port：" + clientPort);
        System.out.println("The info：" + new String(data, 0, len));
        // feedback to Client
        byte[] b = "OK".getBytes();
        DatagramPacket sendPacket = new DatagramPacket(b, b.length, clientAddress, clientPort);
        // send
        socket.send(sendPacket);
    } catch (Exception e) {
        e.printStackTrace();
    }
}
}

客户

public class MulUDPClient {
public static void main(String[] args) {
        DatagramSocket socket = null; 
        DatagramPacket sendPacket; 
        DatagramPacket receivedPacket; 
        String serverHost = "localhost"; 
        int serverPort = 10010; 
        try {
            socket = new DatagramSocket();
            InetAddress address = InetAddress.getByName(serverHost);
            byte[] b = new byte[1024];
            receivedPacket = new DatagramPacket(b, b.length);
            System.out.println("Client ready!");
            for (int i = 0; i < 30; i++) {
                // get the current time
                Date d = new Date(); 
                String content = d.toString(); 
                byte[] data = content.getBytes();
                sendPacket = new DatagramPacket(data, data.length, address, serverPort);
                socket.send(sendPacket);
                System.out.println("already send time");
                Thread.sleep(10);

                // receive packet from Server
                socket.receive(receivedPacket);
                byte[] response = receivedPacket.getData();
                int len = receivedPacket.getLength();
                String s = new String(response, 0, len);
                System.out.println("the feedback from Server：" + s);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                // close the connection
                socket.close();
            } catch (Exception e) {
            }
        }
    }
}

在两个终端分别运行Server和Client后的**Result**：

服务器

Server start!
Fri Nov 23 14:52:02 CST 2018
a thread have been set up

客户

Client ready!
already send time

从结果可知，Client 发送了一个 UDP 数据包，Server 正确解析并创建了一个线程。那么程序正在等待...

困扰了我几天，谁能帮我解决一下？ :)。谢谢！

编辑

客户

**不能**工作

for (int i = 0; i < 30; i++) {
    Thread writerWorker = new WriterWorker(socket);
    writerWorker.start();
    Thread readerWorker = new ReaderWorker(socket);
    readerWorker.start();
}

**可以**工作

for (int i = 0; i < 30; i++) {
    Date d = new Date(); 
    String content = d.toString(); 
    byte[] data = content.getBytes();
    sendPacket = new DatagramPacket(data, data.length, address, serverPort);
    socket.send(sendPacket);
    Thread.sleep(10);
    Thread readerWorker = new ReaderWorker(socket);
    readerWorker.start();
}

作家工作者

public class WriterWorker extends Thread {
    DatagramSocket socket;
    String serverHost = "localhost";
    int serverPort = 10000;
    DatagramPacket sendPacket;

    public WriterWorker(DatagramSocket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        try {
            InetAddress address = InetAddress.getByName(serverHost);
            Date d = new Date();
            String content = d.toString();
            byte[] data = content.getBytes();
            sendPacket = new DatagramPacket(data, data.length, address, serverPort);
            socket.send(sendPacket);
            System.out.println("already send time");

        } catch (Exception e) {
            // TODO: handle exception
        }
    }
}

Answer 1

您的逻辑存在缺陷，当您执行 socket.receive(receivedPacket); 时，这将使工作人员等待某些数据报数据包确实到达...

通过套接字处理异步通信的正确方法如下（这里是客户端的示例）

socket = new DatagramSocket();
Thread readerWorker = new ReaderWorker(socket);
readerWorker.start();

Thread writerWorker = new WriterWorker(socket);
writerWorker.start();

这样您就可以将读取和写入分开到不同的线程中，而阻塞方法socket.receive(...) 不会停止您的写入线程...

每个工人都会实现自己的工人循环

作家循环：

while(true){
    if (sendPacket!= null){
        socket.send(sendPacket);
    }
    Thread.sleep(10);
}

阅读器循环：

while(true){
    socket.receive(receivedPacket);
    handlePacket(receivedPacket);
}

注意：

那段代码完全是我写的，我没有检查正确的语法

Answer 2

删除客户端中的“Thread.sleep(10)”