为什么关闭客户端后服务器停止运行？

Question

I am writing my first Client-Server program in Java using Sockets. I am using Eclipse as the IDE. When I am testing the communication between both programs (server and client) I run first the server using the command prompt and then I run the client in Eclipse. Everything works fine, I can read from and write to the socket, however, when I close the client program in Eclipse, the server program closes too. Why is this happening? The server is supposed to be running by itself in the command prompt, it is not dependent on a client.

Also I would like to know if there is any possibility I can run both programs in Eclipse instead of opening the server in the command prompt first.

Here is my code for both programs:

Server:

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class ServerPrg {

public static void main(String[] args) {

    System.out.println("Server is running.....");

    try {
        ServerSocket socketSer = new ServerSocket(4444);
        Socket clientSocket = socketSer.accept();

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

        BufferedReader stdIn = (new BufferedReader (new InputStreamReader(System.in)));

        System.out.println("Client: " + in.readLine());

        String input ;
        while((input = stdIn.readLine()) != null)
            {   out.println(input);
                System.out.println("Client: " + in.readLine());
            }
    }

    catch (Exception e) {System.out.println("CAN'T CREATE SERVERSOCKET. PROBABLY THE PORT IS BEING USED   " + e);}

} //end main
} //end public class

Client:

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

public class ClientPrg {

public static void main(String[] args) {

    int portNumber = 4444;

    try {
        Socket clientSocket = new Socket("127.0.0.1", portNumber);
        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

        BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));

        String input;
        while ((input = stdIn.readLine()) != null)
        {
            out.println(input);
            System.out.println("Server: " + in.readLine());
        }


    } catch(Exception e)
    {
        System.out.println(e);
        System.out.println("CAN'T CONNECT TO THE SERVER");
    }

} //end main
} // end public class

Answer 1

Your server lacks a loop around accepting client sockets.

This means that after your client socket is accepted, it will exit because there is no flow control element that will have it attempt to accept a second client socket.

A simple loop around accepting client sockets is probably not exactly what you want. That is because there will be only one Thread in the solution, which means that while a client is being handled, other clients won't be able to be accepted.

There are many ways to handle the situation above. One of the simplest is to create a thread for every accepted client to handle the client's communications. While this is initially simple, it does not scale very well. With a large number of clients, the thread count will rise, and most computers can handle many more network connections than threads.

The scope of talking about services that scale well is far to big to address here; but, after you get familiar with one thread per client processing, start looking at Java NIO.