Java UDP 客户端未从服务器接收（简单的客户端服务器 udp 代码）答案

【问题标题】：Java UDP client not receiving from server(simple client server udp code)Java UDP 客户端未从服务器接收（简单的客户端服务器 udp 代码）
【发布时间】：2017-06-10 20:54:44
【问题描述】：

我是 java 网络的新手，我做了一个客户端-服务器 udp 程序。服务器端工作正常，但客户端没有从服务器接收任何东西。请更正错误。服务器端完全运行，但客户端直到结束才工作。任何帮助都会很棒。

public class Client {
    public static void main (String args[]) throws Exception {
        DatagramSocket s = new DatagramSocket();
        String msg = "Hello! ,from client. ";
        byte[] b = msg.getBytes();
        InetAddress ia = InetAddress.getLocalHost();
        DatagramPacket dp = new DatagramPacket(b, b.length, ia, 9999);
        s.send(dp);

        byte[] b2 = new byte[1024]; //byte array
        DatagramPacket dip = new DatagramPacket(b2, b2.length);
        s.receive(dip);
        String str = new String(dip.getData());
        System.out.println("From server" + str);
    }
}

public class Server {
    void run() throws Exception {
        DatagramSocket ds = new DatagramSocket(9999);
        byte [] b = new byte[1024];

        DatagramPacket dp = new DatagramPacket(b, b.length);
        ds.receive(dp);
        String msg = new String(dp.getData());
        System.out.println("Message from client:" + msg);

        //giving back to client
        String str = "HI!, from server.";
        byte[] b2 = str.getBytes();
        InetAddress ia = InetAddress.getLocalHost();
        DatagramPacket dop = new DatagramPacket(b2, b2.length, ia, 9999);
        ds.send(dop);
        System.out.println("Message sent back");
        ds.close();
    }

    public static void main(String args[]) throws Exception {
        Server server = new Server();
        server.run();
    }
}

【问题讨论】：

标签： java networking network-programming udp

【解决方案1】：

您的服务器正在向 localhost 的 9999 端口发送所有响应。您需要更新服务器，以便它读取发件人的地址：

InetAddress ia = dp.getAddress();
int port = dp.getPort();
DatagramPacket dop = new DatagramPacket(b2, b2.length, ia, port);

【讨论】：

【解决方案2】：

错误是您的服务器和客户端在同一主机上运行，因此它们必须侦听不同的端口，如下所示：

服务器

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

public class Server {
    void run() throws Exception {
        DatagramSocket ds = new DatagramSocket(9999);
        byte [] b = new byte[1024];

        DatagramPacket dp = new DatagramPacket(b, b.length);
        ds.receive(dp);
        String msg = new String(dp.getData(),0,dp.getLength(),"UTF-8");
        System.out.println("Message from client:" + msg);

        //giving back to client
        String str = "HI!, from server.";
        byte[] b2 = str.getBytes();
        InetAddress ia = InetAddress.getLocalHost();

        DatagramPacket dop = new DatagramPacket(b2, b2.length, ia, 9998);
        ds.send(dop);
        System.out.println("Message sent back");
        ds.close();
    }

    public static void main(String args[]) throws Exception {
        Server server = new Server();
        server.run();
    }
}

和客户

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

public class Client {
    public static void main (String args[]) throws Exception {
        DatagramSocket s = new DatagramSocket(9998);
        String msg = "Hello! ,from client. ";
        byte[] b = msg.getBytes();
        InetAddress ia = InetAddress.getLocalHost();
        DatagramPacket dp = new DatagramPacket(b, b.length, ia, 9999);
        s.send(dp);

        byte[] b2 = new byte[1024]; //byte array
        DatagramPacket dip = new DatagramPacket(b2, b2.length);
        s.receive(dip);
        String str = new String(dip.getData(),0,dip.getLength(),"UTF-8");
        System.out.println("From server" + str);
    }
}

【讨论】：