Java Server Socket Socket program stuck while reading

i have 2 programm one is a server and the other the client , i have some other class who represent geomtric shape. In the client with the scanner the user write the caracteristics of the shape width,length for a rectangle as an example. the he create an object and send it to the server , the server receive the object calculate area and perimeter and send them to the client. This should happen until the user press enter in the client instead of caracteristics. And i don’t know why but the first loop work good but the second one i type my caracteristics and then nothing happen anymore and my programms are stuck . Maybe you can see my error here are the 2 programm :

Ps: i’m French so sorry for the french word use for my variable’s name Server:

ServerSocket sockConn = null;
    Socket sockComm = null;
    try{
        sockConn = new ServerSocket();
        InetSocketAddress isa = new InetSocketAddress(portServ);//port + wildcard.
        sockConn.bind(isa);
        System.out.println("Server Launched !");
        int nbForme = 0;
        int compteur = 0;
        while(true){
            sockComm = sockConn.accept();
            ObjectInputStream is = new ObjectInputStream(sockComm.getInputStream());
            ObjectOutputStream os = new ObjectOutputStream(sockComm.getOutputStream());
            //nbForme = is.readInt();
            //System.out.println("nombre de forme a traiter recu : "+nbForme);              
            FormeGeo forme = (FormeGeo)is.readObject();
            
            System.out.println("Forme recu "+forme.toString());
            os.writeDouble(forme.perimetre());
            os.flush();
            os.writeDouble(forme.aire());
            os.flush();
            //compteur++;
            
            //System.out.println("Nombre de forme demande atteint");
            //is.close();
            //os.close();
             
        }

And my client :

            String ipServ = args[0];
        sockComm = new Socket();
        InetSocketAddress connect= new InetSocketAddress(ipServ,portServ);
        sockComm.connect(connect);
        //          System.out.print("Entrez un nombre de forme a saisir : ");
        //sc = new Scanner(System.in);
        //nbForme = sc.nextInt();
        //sc = null;
        //System.out.println(nbForme);
        //System.out.println("Envoi du nombre de forme a traiter");

        //os.writeInt(nbForme);
        //os.flush();
        while(!line.equals("")){
            System.out.println("Saisissez les valeurs d'une forme ou appuyer sur entrer pour stopper le programme");
            sc = new Scanner(System.in);
            line = sc.nextLine();
            os = new ObjectOutputStream(sockComm.getOutputStream());
            is = new ObjectInputStream(sockComm.getInputStream());
            
            
            if(line.equals("")){
                System.out.println("Fin du programme");
                break;
            }else if(!line.contains(",")){
                rayon = Double.parseDouble(line);
                if(rayon<=0.0){
                    System.out.println("Longueur du rayon doit être positive");
                    System.exit(2);
                }   
                FormeGeo rond = new Rond(rayon);
                os.writeObject(rond);
            }else{
                String[] numbers = line.split(","); 
                if(numbers.length==2){
                    longueur = Double.parseDouble(numbers[1]);
                    largeur = Double.parseDouble(numbers[0]);
                    FormeGeo rec= new Rectangle(largeur,longueur);
                    os.writeObject(rec);
                }else{
                    System.out.println("Erreur trop d'arguments pour un rectangle !");
                    System.exit(3);
                }
            }
            os.flush();

            double perimetre = is.readDouble();
            double aire = is.readDouble();
            
            System.out.println("perimetre et  aire renvoye par le serveur respectivement : "+perimetre+" et "+aire);
            //compteur++;
            //is.close();
        }
        is.close();
        os.close();

Answer

Your server socket does the following:

Wait for a connection to happen, and accept it. (this is sockConn.accept())
Receive a request from that connection
Send a response to that connection
Wait for a connection to happen, and accept it.
Receive a request from that connection
Send a response to that connection
…

i.e. your server only expects one request per connection.

Your client does this:

Connect to the server
Send a request
Receive a response
Send a request
Receive a response
…

When your client is waiting for the 2nd response, your server is waiting for the 2nd connection, so nothing happens.

You can fix it by doing one of these things:

Make the client start a new connection for every request
Make the server handle many requests on the same connection (instead of waiting for a new one)
Make the server start a new thread for every connection, so it can process several connections at the same time

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Answer