Question

我想了解UDP无连接客户端 - 服务器对。我在Book Computer Networking：Top Top Down方法中得到了一些代码。该计划如下： - 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。我很想知道如何修复Client的端口，就像我们在给定的java程序中为Server做的那样，以便可以在特定端口上将消息返回给Client。

例如，如果客户端将向服务器发送UDP消息，服务器将在端口号9876上启动并运行，并将原始消息返回到端口9877上的客户端。请帮助。

Answer 1

您不需要客户端的固定端口，只需要客户端需要固定的IP地址。您自己的代码应该已经正常工作。但是还有其他问题：

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

错误。它应该是String sentence = 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);

此代码会将请求的回复发送回来。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。

如何在UDP无连接客户端的固定端口上运行客户端程序 - java

1 个答案: