Question

I’m programming a client server app. I’m wondering to end the connection, which side should decide to end it, client or server?

Then if for example the client did it, should the server still keep open or not?

Suppose we have the below codes for each client and server:

           socket = new Socket("127.0.0.1",3000);
........

            socket.close();

or

            serverSocket = new ServerSocket(3000);
            socket = serverSocket.accept();
......

            serverSocket.close();

EDIT:
according to the matt’s answer, i pot my code here and let see why my code doesnt work:

generally, i have a Jframe program as client which will connect to a server and while its open, i want the connection being alive, since it send info to the server and server should response for the result. but if i dont use closing the socket from server it gives an error and if i use, after once calculation, it closes the connection:

Server

        private static PrintWriter toClient;
        private static BufferedReader fromClient;


  public static void run() throws IOException, SAXNotRecognizedException, SAXNotSupportedException, ParserConfigurationException, SAXException, XPathExpressionException
        {
  
        
        System.out.println("Server is waiting for connections...");
   
        while(true)
        {
                 openStreams();
                  processClient();
                  closeStreams();
 }
     
    }

OpenStream:

  public static void openStreams() throws IOException, SAXNotRecognizedException, SAXNotSupportedException, ParserConfigurationException, SAXException, XPathExpressionException
            {
            serverSocket = new ServerSocket(3000);
            socket = serverSocket.accept();
                System.out.println("Connected");

             toClient = new PrintWriter(socket.getOutputStream(),true);
            
            fromClient = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            

            }

Closestearms:

   public static void closeStreams() throws IOException
            {
            fromClient.close();
            toClient.close();
            socket.close();
            serverSocket.close();
                System.out.println("Disconnected");
        }
          

the error i receive if i remove the closestream();

at java.net.PlainSocketImpl.bind(PlainSocketImpl.java:359)
    at java.net.ServerSocket.bind(ServerSocket.java:319)
    at java.net.ServerSocket.<init>(ServerSocket.java:185)
    at java.net.ServerSocket.<init>(ServerSocket.java:97)

Answer 1

Depends on your application’s logic. Both are valid, and you must make sure your code is correct in both cases, since if the connection is broken “involuntarily” (like a network drop), it will appear to both sides as if the other side had closed the connection.

So your code must handle both cases gracefully.

Your closing code is suspicious: you’re closing the listening socket, which is unusual. You should only close the listening socket when you don’t want any more incoming connections (i.e. usually for a server, when you’re shutting down the server).
Only close the socket you got from accept to end that “conversation”, and don’t re-open the server listening socket. (The exception you’re getting might be an “Address already in use” in this case. See How to set reuse address option for a datagram socket in java code? for an example of how to avoid that specific problem.)