为什么第二次拒绝连接？

Question

I am trying to forward a message from a client to a server and again from that server to another server. For the first time it works fine but when I type second message its say "Unexpected exception: Connection refused" why is it so?

Here is the code

Client.java

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

public class Client {
    private Socket socket = null;
    private DataInputStream console = null;
    private DataOutputStream streamOut = null;

    @SuppressWarnings("deprecation")
    public Client(String serverName, int serverPort) {
        System.out.println("Establishing connection. Please wait ...");
        try {
            socket = new Socket(serverName, serverPort);
            System.out.println("Connected: " + socket);
            start();
        } catch (UnknownHostException uhe) {
            System.out.println("Host unknown: " + uhe.getMessage());
        } catch (IOException ioe) {
            System.out.println("Unexpected exception: " + ioe.getMessage());
        }
        String line = "";
        while (!line.equals("exit")) {
            try {
                line = console.readLine();
                streamOut.writeUTF(line);
                streamOut.flush();
            } catch (IOException ioe) {
                System.out.println("Sending error: " + ioe.getMessage());
            }
        }
    }

    public void start() throws IOException {
        console = new DataInputStream(System.in);
        streamOut = new DataOutputStream(socket.getOutputStream());
    }

    public void stop() {
        try {
            if (console != null)
                console.close();
            if (streamOut != null)
                streamOut.close();
            if (socket != null)
                socket.close();
        } catch (IOException ioe) {
            System.out.println("Error closing ...");
        }
    }

    public static void main(String args[]) {
        @SuppressWarnings("unused")
        Client client = null;
        if (args.length != 2)
            System.out.println("Usage: java Client host port");
        else
            client = new Client(args[0], Integer.parseInt(args[1]));
    }
}

AuServer.java

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

public class AuServer {
    private Socket socket = null;
    private Socket publishingsocket = null;
    private ServerSocket server = null;
    private DataInputStream streamIn = null;
    private String line = null;
    private DataOutputStream streamOut = null;

    public AuServer(int port) {
        try {
            System.out.println("Binding to port " + port + ", please wait  ...");
            server = new ServerSocket(port);
            System.out.println("Server started: " + server);
            System.out.println("Waiting for a client ...");
            socket = server.accept();
            System.out.println("Client accepted: " + socket);
            open();
            boolean done = false;
            while (!done) {
                try {
                    line = streamIn.readUTF();
                    System.out.println(line);
                    done = line.equals("exit");
                } catch (IOException ioe) {
                    done = true;
                }
                forward(line, 50090);
            }
            close();
        } catch (IOException ioe) {
            System.out.println(ioe);
        }
    }

    public void forward(String line, int port) {
        try {
            publishingsocket = new Socket("localhost", port);
            streamOut = new DataOutputStream(publishingsocket.getOutputStream());
            streamOut.writeUTF(line);
            streamOut.flush();
        } catch (UnknownHostException uhe) {
            System.out.println("Host unknown: " + uhe.getMessage());
        } catch (IOException ioe) {
            System.out.println("Unexpected exception: " + ioe.getMessage());
        } finally {
            try {
                publishingsocket.close();
            } catch (IOException e) {
                System.out.println(e.getMessage());
            }
        }
    }

    public void open() throws IOException {
        streamIn = new DataInputStream(new BufferedInputStream(
                socket.getInputStream()));
    }

    public void close() throws IOException {
        if (socket != null)
            socket.close();
        if (streamIn != null)
            streamIn.close();
    }

    public static void main(String args[]) {
        @SuppressWarnings("unused")
        AuServer server = null;
        if (args.length != 1)
            System.out.println("Usage: java Server port");
        else
            server = new AuServer(Integer.parseInt(args[0]));
    }
}

AppServer.java

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

public class AppServer {
    private Socket socket = null;
    private ServerSocket server = null;
    private DataInputStream streamIn = null;

    public AppServer(int port) {
        try {
            System.out.println("Binding to port " + port + ", please wait  ...");
            server = new ServerSocket(port);
            System.out.println("Server started: " + server);
            System.out.println("Waiting for a client ...");
            socket = server.accept();
            System.out.println("Client accepted: " + socket);
            open();
            boolean done = false;
            while (!done) {
                try {
                    String line = streamIn.readUTF();
                    System.out.println(line);
                    done = line.equals("exit");
                } catch (IOException ioe) {
                    done = true;
                }
            }
            close();
        } catch (IOException ioe) {
            System.out.println(ioe);
        }
    }

    public void open() throws IOException {
        streamIn = new DataInputStream(new BufferedInputStream(
                socket.getInputStream()));
    }

    public void close() throws IOException {
        if (socket != null)
            socket.close();
        if (streamIn != null)
            streamIn.close();
    }

    public static void main(String args[]) {
        @SuppressWarnings("unused")
        AppServer server = null;
        server = new AppServer(50090);
    }
}

Pls help............

Answer 1

A typically socket server would require some kind of loop where in the server socket would accept incoming connections and spawn a new Thread which would be responsible for actually handling the new Socket connection, leaving the current thread free to continue processing any new incoming connections, for example...

server = new ServerSocket(port);

while (continueAccpetingConnections) {

    Socket socket = server.accept();
    Thread thread = new Thread(new SocketHandler(socket));
    thread.start();

}

The SocketHandler would implement Runnable and provide a constructor that would accept a Socket variable.

It would then be the responsibility of the SocketHandler to actually perform the communications required by the server.

Now, if you wanted to have only one active connection, you might use

while (continueAccpetingConnections) {

    Socket socket = server.accept();
    process(socket);

}

Which would prevent any new connections until process returned...

Answer 2

Your server is written to accept exactly one connection, process it in the same thread, and then exit. If you want to keep accepting connections, do so, in a loop. If you want to handle clients concurrently, start a new thread to handle each accepted socket.