UDP数据报在Java中仅显示第一个字符

Question

我正在尝试创建一个Echo服务器客户端UDP应用程序。客户端应该发送20多个号码，服务器只会将它们发送回。然而，据我所知，它只显示来自String的first character正在被发送。我向教授寻求帮助，但他也不明白。帮点忙就好了。谢谢!

客户。爪哇：

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;

public class client {
    public static void main(String[] args) {
        DatagramSocket socket;
        try {
            socket = new DatagramSocket();
            InetAddress address = InetAddress.getByName("localhost");
            byte[] buf = new byte[256];
            for (Integer i = 1; i < 21; i++) {
                buf = i.toString().getBytes();
                DatagramPacket packet = new DatagramPacket(buf, buf.length, address, 4445);
                socket.send(packet);
                packet = new DatagramPacket(buf, buf.length);
                socket.receive(packet);
                String received = new String(packet.getData(), 0, packet.getLength());
                System.out.println("Server: " + received);
            }
            socket.close();
        } catch (SocketException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

服务器。爪哇：

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;

public class server {
    public static void main(String argsp[]) {
        DatagramSocket socket;
        try {
            socket = new DatagramSocket(4445);
            byte[] buf = new byte[256];
            DatagramPacket packet = new DatagramPacket(buf, buf.length);
            while (true) {
                socket.receive(packet);
                String message = new String(packet.getData(), 0, packet.getLength());
                System.out.println("Client: " + message);
                buf = message.getBytes();
                InetAddress address = packet.getAddress();
                int port = packet.getPort();
                packet = new DatagramPacket(buf, buf.length, address, port);
                socket.send(packet);
            }
        } catch (SocketException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

客户端输出：

Server: 1
Server: 2
Server: 3
Server: 4
Server: 5
Server: 6
Server: 7
Server: 8
Server: 9
Server: 1
Server: 1
Server: 1
Server: 1
Server: 1
Server: 1
Server: 1
Server: 1
Server: 1
Server: 1
Server: 2

服务器输出：

Client: 1
Client: 2
Client: 3
Client: 4
Client: 5
Client: 6
Client: 7
Client: 8
Client: 9
Client: 1
Client: 1
Client: 1
Client: 1
Client: 1
Client: 1
Client: 1
Client: 1
Client: 1
Client: 1
Client: 2

Answer 1

每次你收到一个数据报，DatagramPacket就会缩小到原来的长度。因此，在您的服务器中，它在第一次接收后收缩为1。您需要在接收lopo中重新创建它，或者至少在循环顶部重置它的长度