Java getting ObjectInputStream ObjectOutputStream from a socket

Question

I have an application that is based on server- multiple clients interaction.This is the thread that i use in the server class to create a new thread where i accept all the new sockets:

    Thread acceptingThread = new Thread(new Runnable() {

        @Override
        public void run() {
            while (true) {
                try {
                    Socket s = serverSocket.accept();
                    listaSocket.add(s);
                    listaOis.add(new ObjectInputStream(s.getInputStream()));
                    listaOos.add(new ObjectOutputStream(s.getOutputStream()));
                    System.out.println("Client connected");
                } catch (IOException ex) {
                    Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
                }
            }

        }

    });
    acceptingThread.start();




private ServerSocket serverSocket;
private ArrayList<Socket> listaSocket;
private ArrayList<ObjectInputStream> listaOis;
private ArrayList<ObjectOutputStream> listaOos;

The lines that block the programs are :

                    listaOis.add(new ObjectInputStream(s.getInputStream()));
                    listaOos.add(new ObjectOutputStream(s.getOutputStream()));

I think serverSocket.accept() is blocking program, it wait for new request to come. — Nikesh Joshi
– Nikesh Joshi, Commented Apr 11, 2017 at 6:38
In my client i'm making a socket that connects to this server.In s i get the socket from the client.ObjectInputStream takes an InputStream in his constructor.I get that from s.getInputStream() — Dante
– Dante, Commented Apr 11, 2017 at 6:40

Carlos Miranda · Accepted Answer · 2017-04-11 07:34:20Z

Your code is blocking in this particular line:

                    listaOis.add(new ObjectInputStream(s.getInputStream()));

Take note of the behavior of this ObjectInputStream constructor. From the Javadoc:

Creates an ObjectInputStream that reads from the specified InputStream. A serialization stream header is read from the stream and verified. This constructor will block until the corresponding ObjectOutputStream has written and flushed the header.

Getting the InputStream from the incoming connection means that serialized data needs to be sent through the connection. This means that you have to do the following before the constructor will proceed:

Connect from the client side. I presume you are already doing this since you can get through socket.accept()
Open an OutputStream using the new connection.
Wrap the OutputStream with an ObjectOutputStream.
Send some data through the ObjectOutputStream (i.e. write some serializable data into it and flush).

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