java.net.绑定(bind)异常 : Address already in use: Cannot bind

Question

对不起，我已经搜索过了，但似乎所有的答案都不能解决我的问题。尝试创建 ServerSocket 以回复多个客户端消息时出现此错误。

我的服务器代码:

package Server;

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

public class Server {
    public final static int defaultPort = 7;

    public static void main(String[] args) {
        try {
            ServerSocket ss = new ServerSocket(defaultPort);            
            int i = 0;
            while (true) {
                try {
                    System.out.println("Server is running on port "
                            + defaultPort);
                    Socket s = ss.accept();
                    System.out.println("Client " + i + " connected");
                    RequestProcessing rp = new RequestProcessing(s, i);
                    i++;
                    rp.start();
                } catch (IOException e) {
                    System.out.println("Connection Error: " + e);
                }
            }
        } catch (IOException e) {
            System.err.println("Create Socket Error: " + e);
        } finally {

        }
    }
}

class RequestProcessing extends Thread {
    Socket channel;
    int soHieuClient;

    public RequestProcessing(Socket s, int i) {
        channel = s;
        clientNo = i;
    }

    public void run() {
        try {
            byte[] buffer = new byte[6000];
            DatagramSocket ds = new DatagramSocket(7);          
            while (true) {  
                DatagramPacket incoming = new DatagramPacket(buffer,
                        buffer.length);
                ds.receive(incoming);
                String theString = new String(incoming.getData(), 0,
                        incoming.getLength());
                System.out.println("Client " + clientNo 
                        + " sent: " + theString);
                if ("quit".equals(theString)) {
                    System.out.println("Client " + clientNo 
                            + " disconnected");
                    ds.close();
                    break;
                }
                theString = theString.toUpperCase();
                DatagramPacket outsending = new DatagramPacket(
                        theString.getBytes(), incoming.getLength(),
                        incoming.getAddress(), incoming.getPort());
                System.out.println("Server reply to Client "
                        + clientNo + ": " + theString);
                ds.send(outsending);
            }
        } catch (IOException e) {
            System.err.println(e);
        }

    }
}

和我的客户代码:

package Client;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.Socket;

public class Client extends Object {
    public final static int serverPort = 7;

    public static void main(String[] args) {
        try {

            DatagramSocket ds = new DatagramSocket();
            InetAddress server = InetAddress.getByName("192.168.109.128");
            Socket s = new Socket("192.168.109.128", 7);            
            String theString = "";
            do {
                System.out.print("Enter message: ");
                InputStreamReader isr = new InputStreamReader(System.in);
                BufferedReader br = new BufferedReader(isr);
                theString = br.readLine();
                byte[] data = theString.getBytes();
                DatagramPacket dp = new DatagramPacket(data, data.length,
                        server, serverPort);

                ds.send(dp);
                System.out.println("Sent to server server: " + theString);

                byte[] buffer = new byte[6000];

                DatagramPacket incoming = new DatagramPacket(buffer,
                        buffer.length);
                ds.receive(incoming);
                System.out.print("Server reply: ");
                System.out.println(new String(incoming.getData(), 0, incoming
                        .getLength()));

            } while (!"quit".equals(theString));
            s.close();
        } catch (IOException e) {
            System.err.println(e);
        }
    }
}

与第一个客户端连接，它工作顺利。但是从第二个客户端，它抛出 java.net.BindException: Address already in use: Cannot bind。第二个Client也可以收发消息，但是Client No还是0。

Server is running on port 7
Client 0 connected
Server is running on port 7
Client 0 sent: msg 0
Server reply to Client 0: MSG 0
Client 1 connected
Server is running on port 7
java.net.BindException: Address already in use: Cannot bind
Client 0 sent: msg 1 <<-- this one is sent from client 1 but Client No is 0
Server reply to Client 0: MSG 1

Answer 1

因此，在 RequestProcessing.run 中，您决定忽略在构造函数中接收到的套接字，并在与您正在监听的端口相同的端口上打开一个 DatagramSocket。你期望它会发生什么？

class RequestProcessing extends Thread {
    Socket channel;
    int soHieuClient;

    public RequestProcessing(Socket s, int i) {
        // *****************
        // The processor should be using this socket to communicate
        // with a connected client *using TCP Streams*
        channel = s;
        clientNo = i;
    }

    public void run() {
       try {
           byte[] buffer = new byte[6000];
           // *****************************
           // But, instead of using the this.channel, your code
           // decides to ignore the TCP socket,
           // then open another UDP *"server-side like"* socket.
           // First time it's OK, but the second thread attempting
           // to open another DatagramSocket on the same port will fail.
           // It's like attempting to open two TCP ServerSockets on the
           // same port
           DatagramSocket ds = new DatagramSocket(7);  

[额外]

您需要决定要使用的协议(protocol):如果您使用 ServerSocket/Socket 对，那么您可能需要 TCP 通信，所以没有 DatagramSockets.

如果您需要 UDP 通信，ServerSocket/Socket 与您的方法无关，您需要使用 DatagramSocket。构造它:

1. > with a port on the serverside - 并且只做一次。
2. > without any port for the client side然后用服务器地址和端口限定每个 DatagramPackets。

请参阅 Oracle 站点上的教程 Datagram client/server configurations .