Question

I have a server-client pair and I want to create a listener on the client end for new server responses. I am not sure how to do this, right now I can only interact in a direct synchronous way.

Here is the server:

public class TestServer {

public static void main(String[] args) throws Exception {

    TestServer myServer = new TestServer(); 
    myServer.run(); 

}

private void run() throws Exception {

    ServerSocket mySS = new ServerSocket(4443);     

    while(true) {

        Socket SS_accept = mySS.accept(); 

        BufferedReader myBR = new BufferedReader(new InputStreamReader(SS_accept.getInputStream()));

        String temp = myBR.readLine(); 
        System.out.println(temp); 


        if (temp!=null) {

            PrintStream serverPS = new PrintStream(SS_accept.getOutputStream()); 
            serverPS.println("Response received: " + temp); 

        }

    }
}

}

As you can see, it sends a response when it gets one. However in general I won’t be sure when other servers I use send responses, so I would like to create an asynchronous listener (or at least poll the server for a response every half-second or so).

Here is what I’m trying on the client end:

protected static String getServerResponse() throws IOException {

    String temp;
    try {
        BufferedReader clientBR = new BufferedReader(new InputStreamReader(mySocket.getInputStream())); 
        temp = clientBR.readLine(); 
    } catch (Exception e) {
        temp = e.toString(); 
    }

    return temp; 
}

And just for reference, yes, sending over data from client to server works fine (it System.out’s the data correctly). However, when I call the above function to try and retrieve the server response, it just hangs my application, which is an Android application in case that’s relevant.

What I want from a function is just the ability to ask the server if it has data for me and get it, and if not, then don’t crash my damn app.

Answer 1

On the client side create a ConnectionManager class which will handle all the socket I/O. The ConnectionManager‘s connect() method will create and start a new thread which will listen for server responses. As soon as it will receive a response it will notify all the ConnectionManager‘s registered listeners. So in order to receive asynchronously the server responses you will have to register a listener in ConnectionManager using its register(SomeListener) method.

Also, you can have a look at JBoss Netty which is an asynchronous event-driven network application framework. It greatly simplifies and streamlines network programming such as TCP and UDP socket server.