Question

我有简单的UDP客户端和服务器代码。当服务器从客户端获取请求时，我想从客户端发送的数据和一些其他数据中形成一个回复，如代码所示。

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

public class UDPClient {

public static void main(String args[]){ 
    // args give message contents and destination hostname
    DatagramSocket aSocket = null;
    try {
        aSocket = new DatagramSocket();    
        byte [] m = args[0].getBytes();
        InetAddress aHost = InetAddress.getByName(args[1]);
        int serverPort = 8211;                                                       
        DatagramPacket request =
            new DatagramPacket(m,  args[0].length(), aHost, serverPort);
        aSocket.send(request);                                  
        byte[] buffer = new byte[1000];
        DatagramPacket reply = new DatagramPacket(buffer, buffer.length);   
        aSocket.receive(reply);
        System.out.println("Reply: " + new String(reply.getData()));    
    }catch (SocketException e){System.out.println("Socket: " + e.getMessage());
    }catch (IOException e){System.out.println("IO: " + e.getMessage());
    }finally {if(aSocket != null) aSocket.close();}
}

}

public class UDPServer {

  public static void main(String args[]){ 
        DatagramSocket aSocket = null;
        try{
            aSocket = new DatagramSocket(8211);
                    // create socket at agreed port
            byte[] buffer = new byte[1000];
            while(true){


                buffer = ("Hello "+new String(request.getData()).toUpperCase()+" Goodbye").getBytes();

                System.out.print("Replying to client: "+buffer);

                DatagramPacket reply = new DatagramPacket(buffer, buffer.length, 
                    request.getAddress(), request.getPort());
                aSocket.send(reply);
            }
        }catch (SocketException e){System.out.println("Socket: " + e.getMessage());
        }catch (IOException e) {System.out.println("IO: " + e.getMessage());
        }finally {if(aSocket != null) aSocket.close();}
    }

}

问题是，作为输出我得到：回复客户端：Hello PAUL和客户端收到的相同，Goodbye被省略。为什么要省略？有趣的是，如果我这样做：

buffer = ("Hello "+"Goodbye " +new String(request.getData()).toUpperCase()).getBytes();

输出是Hello Goodbye PAUL，同样发送给客户端。

Answer 1

简单地调用new String(request.getData())是危险的。 DatagramPacket请求不仅仅是你的字符串，而是整个数据包。在转换为字符串之前，您应该使用DatagramPacket提供的其他方法来获取实际数据。

byte[] packet = new byte[request.getLength()]; 
packet = Arrays.copyOfRange(request.getData(), request.getOffset(), request.getLength() + request.getOffset());

//packet now contains just the string portion of your request, use that instead

UDP客户端服务器Java

1 个答案: