Question

I am writing a Java client/server GUI application using sockets and here is the problem:

I have a button to start listening for a specified port:

button actionPerformed method

private void listenButtonActionPerformed(java.awt.event.ActionEvent evt) {                                             
    int port = Integer.parseInt(portTextfield.getText(), 10);

    try {
        socket.listen(port);
    } catch (IOException ex) {
    }
}

Here is the socket.listen method

public static void listen() throws IOException {
    ServerSocket ss = new ServerSocket(port);

    while (true)
        new socket(ss.accept());
}

“socket” class extends “Thread”
So after ss.accept() returns a value it creates new socket instance in separate thread.

After clicking the button the GUI freezes because inside the socket.listen method there is an infinite loop. How can I avoid that?

Answer 1

You have two pitfalls in your design:

1. ss.accept() is a blocking call so your UI will freeze until there is an incoming connection
2. Never run while(true) loops in the EDT.

Instead do the following:

• When the button is clicked create a thread that will start listening for incoming connections.
• Whenever you have an incoming connection, create another thread that will take the incoming client connection and deal with it.