java - 如何在java中的UDP无连接客户端-服务器对的固定端口上运行客户端程序

Question

我正在尝试了解 UDP 无连接客户端-服务器对。我在《计算机网络:自上而下的方法》一书中获得了一些代码。 计划如下:- UDPServer.java:

    import java.io.*;
    import java.net.*;

    class UDPServer
   {
       public static void main(String args[]) throws Exception
       {
        DatagramSocket serverSocket = new DatagramSocket(9876);
        byte[] receiveData = new byte[1024];
        byte[] sendData = new byte[1024];
        while(true)
        {
          DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);                   
          serverSocket.receive(receivePacket);
          String sentence = new String( receivePacket.getData());
          System.out.println("RECEIVED: " + sentence);
          InetAddress IPAddress = receivePacket.getAddress();
          int port = receivePacket.getPort();
          String capitalizedSentence = sentence.toUpperCase();
          sendData = capitalizedSentence.getBytes();
          DatagramPacket sendPacket =
          new DatagramPacket(sendData, sendData.length, IPAddress, port);                   
          serverSocket.send(sendPacket);
          }
      }
    }

UDPClient.java

import java.io.*;
import java.net.*;
class UDPClient
{
    public static void main(String args[]) throws Exception
    {
        BufferedReader inFromUser =
        new BufferedReader(new InputStreamReader(System.in));
        DatagramSocket clientSocket = new DatagramSocket();
        InetAddress IPAddress = InetAddress.getByName("localhost");
        byte[] sendData = new byte[1024];
        byte[] receiveData = new byte[1024];
        String sentence = inFromUser.readLine();
        sendData = sentence.getBytes();
        DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 9876);      
        clientSocket.send(sendPacket);
        DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);       
        clientSocket.receive(receivePacket);
        String modifiedSentence = new String(receivePacket.getData());
        System.out.println("FROM SERVER:" + modifiedSentence);          
        clientSocket.close();
    }
}

在给定的代码中，我们修复了服务器的端口号，即 9876。 我很好奇如何修复客户端的端口，就像我们在给定的 java 程序中为服务器所做的那样，以便可以在特定端口上将消息返回给客户端。

例如，如果 客户端将向服务器发送一条UDP消息，服务器将在端口号9876上启动并运行，并在端口9877上将原始消息返回给客户端。请帮忙。

Answer 1

客户端不需要固定端口，就像客户端不需要固定 IP 地址一样。您自己的代码应该已经可以正常工作。但还有其他问题:

String sentence = new String( receivePacket.getData());

错了。它应该是String Sent = new String( receivePacket.getData(), receivePacket.getOffset(), receivePacket.getLength());。

      System.out.println("RECEIVED: " + sentence);
      InetAddress IPAddress = receivePacket.getAddress();
      int port = receivePacket.getPort();
      String capitalizedSentence = sentence.toUpperCase();
      sendData = capitalizedSentence.getBytes();
      DatagramPacket sendPacket =
      new DatagramPacket(sendData, sendData.length, IPAddress, port);                   
      serverSocket.send(sendPacket);

此代码会将回复发送回请求来源处。一种更简单的方法是使用相同的 DatagramPacket 进行接收和发送，只需更改数据即可。