Client-Server communication; client freezes

[Khalil Salman]

Hi,
the story:
Clients sends a request, server reads that request, and sends a response, lastly client reads the response.

There will be multiple clients so I tried to implement it using threads in the server code to be able to continue listening for new requests.
But in the last step the client freezes when I say read the response from the server. I mean the client sends a request successfully, and the server reads it and responses successfully but the client then cannot get the response; freezes.

Here is the code:

This is for the client:

                String os="";
                //create a fake id
                int lower=1, upper=5000;
                int restId = lower + (int) ( Math.random()*(upper - lower) );
                
                try {
                    Socket socket = new Socket("localhost", 1234);

                    //Send a request                    
                    PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
                    out.print(Integer.toString(restId)); //send the id
                    out.flush();
                    
                   //read the response
                    BufferedReader in = new BufferedReader(new InputStreamReader(
                                        socket.getInputStream()));                    
                    while(!in.ready()){}
                    os=in.readLine(); //Here the freezing point

                    
                    myLabel.setText(os); //display the response
                    
                    in.close();
                    out.close();
                    socket.close();
                }
                catch(Exception e) {
                    System.out.print("Whoops! It didn't work!\n");
                }

And here is the server:

try {
            ServerSocket server = new ServerSocket(1234); //open this port and listen
            while(true){
                Socket socket = server.accept();
                Runnable handler=new Thread(new ResponseSender(socket));
                handler.run();
            }//end of while
        }catch(Exception exc) {
            System.out.print("Whoops! It didn't work!\n");  }

And the server's response sender run() function:

       String restId="",response="true\n";
        try {
            //read the request
            BufferedReader in = new BufferedReader
                        (new InputStreamReader(socket.getInputStream()));                

            while (!in.ready()) {} // busy waiting until the id is completely ready
            restId = in.readLine(); // read the line
            System.out.print("Received rest id: "+restId);
           
            //send the response
            PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
            out.print(response); //send the status
            System.out.println(" Response was sent "+ response+"\n");
            out.flush();
            out.close();
        } catch(Exception exc){}

Thank you for any help..

[Ulf Dittmer]

Dont't println to a Socket: http://developer.apple.com/technotes/tn/tn1157.html

And don't ignore exception: } catch(Exception exc){}
That's a no-no.

[Paul Clapham]

If you really want the server to be multi-threaded then this is wrong:

handler.run();

To start a Thread running, do this:

handler.start();

And "handler" would need to be a Thread, not a Runnable.

[Khalil Salman]

Thank you guys.

Yeah I commented out println() parts and change the Runnable to Thread. And I replaced handler.run() with handler.start().
But nothing changed.

Something else should be missing. Something that I don't know but very critical.
Gosh 15-20 lines of code but I cannot get it working.

[Paul Clapham]

So show us the new code, the version which doesn't use PrintWriter and which writes your exceptions to somewhere you can look at them.

[Khalil Salman]

Alright. Now I see what you mean by saying "don't println to socket."
Don't use PrintWriter!..

Ulf, the link you gave for "don't println to socket" redirects me to somewhere else not to an article.
So please check it for future references.

Thank you guys anyway, the issue is resolved.

Here is the code, (maybe someone needs it in the future)

The server code:

            ServerSocket server = new ServerSocket(1234); //open this port and listen
            while(true){
                Socket socket = server.accept();
                Thread handler=new Thread(new ResponseSender(socket));
                handler.start();
            }//end of while

server's response sender:

            //read the request
            DataInputStream in=new DataInputStream(new BufferedInputStream(socket.getInputStream()));
            restId=in.readUTF();
            System.out.print("Received id: "+restId+".\n");

            //send a response
            DataOutputStream out= new DataOutputStream(socket.getOutputStream());
            out.writeUTF(restId); 

            in.close();
            out.close();
          } catch(UnknownHostException ukex) {
                System.out.print("Unknown host!\n");
          }
            catch(NoRouteToHostException nrex) {
                System.out.print("Unreachable host!\n");
          }
            catch(ConnectException cnex) {
                System.out.print("Connect refused!\n");
          }
            catch(IOException ioex) {
                System.out.print("IO error occured...\n"+ioex.getMessage());
         }

And the client:

                String response;  
                //create a fake id
                int lower=1, upper=5000;
                int restId = lower + (int) ( Math.random()*(upper - lower) );
                
                try {
                    Socket socket = new Socket("localhost", 1234);
                    //send a request
                    DataOutputStream out= new DataOutputStream(socket.getOutputStream());
                    out.writeUTF(Integer.toString(restId));                    
                    
                    //read the response                    
                    DataInputStream in=new DataInputStream(new BufferedInputStream(socket.getInputStream()));
                    response=in.readUTF();

                    
                    myLabel.setText(response);
                    
                    in.close();
                    out.close();
                    socket.close();
                }
                catch(UnknownHostException ukex) {
                    System.out.print("Unknown host!\n");
                }
                catch(NoRouteToHostException nrex) {
                    System.out.print("Unreachable host!\n");
                }
                catch(ConnectException cnex) {
                    System.out.print("Connect refused!\n");
                }
                catch(IOException ioex) {
                    System.out.print("IO error occured...\n"+ioex.getMessage());
                }

[Ulf Dittmer]

Huh, kind of stupid to break long-established URLs; but here is the article.