無法從Java中的UDP服務器接收正確的消息

Question

我正在嘗試使用udp客戶端將消息發送到udp服務器，並使用有關接收到的消息的各種元數據將消息發送回客戶端。 我有這兩節課：

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

public class UdpDateClient {
    public static void main(String[] args) throws IOException {
        String host = "localhost";
        if (args.length > 0)
            host = args[0];
        // get a datagram socket on any available port
        try {
            DatagramSocket socket = new DatagramSocket();
            // send request
            byte[] buf = new byte[2048];
            buf="hi it's Max".getBytes();
            InetAddress address = InetAddress.getByName(host);
            DatagramPacket packet = new DatagramPacket(buf, buf.length, address, 4445);
            socket.send(packet);
            // get response
            packet = new DatagramPacket(buf, buf.length);
            socket.receive(packet);
            // display response
            buf = packet.getData();
            int len = packet.getLength();
            String received = (new String(buf)).substring(0, len);
            System.out.println("From server: " + received);
            socket.close();
        } catch (SocketException e) {
            e.printStackTrace();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

---

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

public class UdpDateServer {
    private DatagramSocket socket = null;
    private boolean moreClients = true;

    public static void main(String[] args) {
        UdpDateServer server = new UdpDateServer();
        server.start();
    }

    public UdpDateServer() {
        try {
            socket = new DatagramSocket(4445);
            System.out.println("server ready...");
        } catch (SocketException e) {
            e.printStackTrace();
            System.exit(1);
        }
    }

    public void start() {
        DatagramPacket packet;
        while (moreClients) {
            try {
                byte[] buf = new byte[2048];
                // receive request
                packet = new DatagramPacket(buf, buf.length);
                socket.receive(packet);
                System.out.println("recieved packet from client: "+new String(packet.getData()));
                // prepare response
                String responseString = "Client's message received: "+new String(packet.getData())+"\n"
                        + "Received on:" +new Date().toString();

                buf = responseString.getBytes();
                System.out.println("buf to be sent from server: "+(new String(buf)));
                System.out.println("buf.length="+buf.length);
                // send the response to "address" and "port"
                InetAddress address = packet.getAddress();
                int port = packet.getPort();
                packet = new DatagramPacket(buf, buf.length, address, port);
                socket.send(packet);
            } catch (IOException e) {
                e.printStackTrace();
                moreClients = false;
            }
        }
        socket.close();
    }
}

我在客戶端得到的只是服務器發送的消息的前11個字節：

客戶端：

來自服務器：客戶是我

服務器端：

服務器就緒...

從客戶端收到的數據包：嗨，這是Max

從服務器發送的buf：接收到客戶端的消息：嗨，這是Max

2015年8月14日星期五16:00:20 IDT

buf.length = 2116

如您所見，客戶端收到的來自服務器的消息被削減了11個字符。

我究竟做錯了什么？

Answer 1

問題是行buf="hi it's Max".getBytes(); is buf="hi it's Max".getBytes(); 客戶代碼。 在這里，您將緩沖區長度設置為11。您的客戶端代碼應類似於以下內容

            DatagramSocket socket = new DatagramSocket();
            // send request
            byte[] buf = "hi it's Max".getBytes();
            InetAddress address = InetAddress.getByName(host);
            DatagramPacket packet = new DatagramPacket(buf, buf.length, address, 4445);
            socket.send(packet);
            // get response
            buf = new byte[2048];
            packet = new DatagramPacket(buf, buf.length);
            socket.receive(packet);
            // display response
            buf = packet.getData();
            int len = packet.getLength();
            String received = (new String(buf)).substring(0, len);
            System.out.println("From server: " + received);
            socket.close();

Answer 2

byte[] buf = new byte[2048];
buf="hi it's Max".getBytes();

在這個buf.length將是11而不是2048！

在您返回的路上

packet = new DatagramPacket(buf, buf.length);
socket.receive(packet);

因為buf.length為11，所以將僅接收11個字節。將第一個塊更改為類似

byte[] buf = new byte[2048];
System.arraycopy("hi it's Max".getBytes(), 0, buf, 0, 11);