Socket.accept() method ?

Question

Hi,
I'm trying to write a networking app. The client seems to work - it sends a String object through an ObjectOutuptStream.
The problem seems to be that the socket.accept() method in the server isnt working!
//PlusServer.java
//Server that takes commands from Android Client, executes commands & finally returns result.
import java.net.*;
import java.io.*;
public class PlusServer
    //instance variables
    static Boolean finished = false;
    //Main method
    public static void main(String[] args)
        System.out.println(" 000 Entered Main method");
        //Disable Security Manager
        //System.setSecurityManager(null);
            try
        ServerSocket listener = new ServerSocket(1234);
        System.out.println("0 setup ServerSocket on port 1234");
            while(!finished)
                Socket client = listener.accept();//wait for connection
                //The program doesn't proceed any further! Why?
                InputStream in = client.getInputStream();
                OutputStream out = client.getOutputStream();
                //read cmd
                ObjectInputStream oin = new ObjectInputStream(in);
                String cmd = (String)oin.readObject();
                if (cmd.equals("Connect"))
                    client.close();
                    finished=true;
                //Send results
                // blah, blah, blah
            listener.close();   
            catch(Exception e){System.out.println("Error: "+e);}
}The code for the client is available in another forum, here:
http://androidforums.com/developer-101/144926-android-network-programming.html#post1333747

Answer 1

If you plan to use ServerSocket for networking in java, you better get much more familiar and friendly with threads, cause you are going to need them.
I can't look at the other forum from work to see what the client code is, but your code looks really funny here.
Some advice, you are obviously new to this part of java coding, stick to sending strings instead of objects while you are new, it is much easier if you just stick to sending strings, and there is nothing you can't do by just sending strings. Even though in some cases sending objects is the better approach, first learn how to do client server communications the easy way and it will then naturally come to you when you should use objects. Your program clearly could have used strings only. And I am willing to bet that you would have possibly seen the problem yourself if you had.
Also, this is a very poor algorithm. What happens if you want to send two objects (or two strings if you adhear to my advice above)? Do you really think it is necessary and sound to have to reconnect the server and client for every objoct/string you want to send between them? In some cases, perhaps not this one since you are communicating with a mobile device it seems, it is ideal to not ever terminate the connection between the client and server, but instead allow threads to handle keeping open lines of communication.
Now, were I a betting man, I would bet that in your client code you are either neglecting to flush at all, or doing it incorrectly. Again I can't see that code so I am not certain, but that is a common mistake for people new to this and its symptoms fit with what you are describing seeing perfectly. I highely recomend using autoflush, especially to someone new to network programming.
JSG
Edited by: JustSomeGuy on Aug 10, 2010 11:29 AM
Edited by: JustSomeGuy on Aug 10, 2010 11:30 AM