简单的服务器/客户端套接字连接？

Question

I am writing a java socket where a server runs and a client connects to the server and the server can read from the clients command line.

First I wanted to connect to the server, here`s the code:

public class Server{
    public static void main(String[] args) throws IOException {

        ServerSocket serverSocket = null;

        try {
            serverSocket = new ServerSocket(10000);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 4444.");
            e.printStackTrace();
            System.exit(1);
        }

        Socket clientSocket = null;
        try {
            clientSocket = serverSocket.accept();
        } catch (IOException e) {
            System.err.println("Accept failed.");
            System.exit(1);
        }

        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
        String inputLine, outputLine;

        out.close();
        in.close();
        clientSocket.close();
        serverSocket.close();
    }

}

and here is my client:

public class Client {
    public static void main(String[] args) throws IOException {

        Socket socket = null;
        PrintWriter out = null;
        BufferedReader in = null;

        try {
            socket = new Socket("taranis", 4444);
            out = new PrintWriter(socket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        } catch (UnknownHostException e) {
            System.err.println("Don't know about host: taranis.");
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Couldn't get I/O for the connection to: taranis.");
            System.exit(1);
        }

        BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
        String fromServer;
        String fromUser;

        while ((fromServer = in.readLine()) != null) {
            System.out.println("Server: " + fromServer);
            if (fromServer.equals("Bye."))
                break;

            fromUser = stdIn.readLine();
            if (fromUser != null) {
                System.out.println("Client: " + fromUser);
                out.println(fromUser);
            }
        }

        out.close();
        in.close();
        stdIn.close();
        socket.close();
    }
}

When I start the server I get "Could not listen on port: 4444."

Why?

UPDATE:

Right now I cannot restart the server again, because I get

java.net.BindException: Address already in use: JVM_Bind
    at java.net.DualStackPlainSocketImpl.bind0(Native Method)
    at java.net.DualStackPlainSocketImpl.socketBind(Unknown Source)
    at java.net.AbstractPlainSocketImpl.bind(Unknown Source)
    at java.net.PlainSocketImpl.bind(Unknown Source)
    at java.net.ServerSocket.bind(Unknown Source)
    at java.net.ServerSocket.<init>(Unknown Source)
    at java.net.ServerSocket.<init>(Unknown Source)

What can I do against that?(I am using windows7)

Answer 1

it seems to me that your server is not listening on port 4444 but instead listening on port 10000 however your client tries to connect to port 4444.

To answer your 2nd problem if you close down the application make sure you actually terminate the it. sometimes if you start the application again you have 2 running and can have a hard time see that 1 of the applications are still open.

Hope i helped else please reply in a comment il check back on you late :)

Answer 2

java.net.BindException: Address already in use: JVM_Bind

usually came out when you haven't terminate properly last execution like in eclipse if you run then run again without terminate you need to "terminate" the process in the console.

Simply mean that the "port" is allready used ( allmost from the same class you launched )

Answer 3

如果您使用的是Eclipse，只需按控制台图块上的红色方块将其停止，然后可以重新连接

Answer 4

Exception : java.net.BindException: Address already in use: JVM_Bind

The solution was to remove the project from the servers tab and right click and run the project as Run on server. This added the project back to the Tomcat 7 and I din't get the BindException error. This was due to closing eclipse the last time you used without stopping the Tomcat server.