Send objects and strings over socket

Question

I've tried several ways to send a string then an object to my server and have my server doSomething() then send a string and an object back to the client but as of now the server isn't even receiving the string. below is my current method.

portion of the Server code where send/receive is done:

try
        {

            ObjectInputStream fromClientObject = new ObjectInputStream(socket.getInputStream());
            ObjectOutputStream toClientObject = new ObjectOutputStream(socket.getOutputStream());

            while(!socket.isClosed())
            {
                //If server has received a message
                if(fromClientObject.available() > 0)
                {
                    //Set received message to string and print
                    String input = fromClientObject.readUTF();
                    System.out.println(input);

                    //If clients sets .register command then register new user
                    if (input.equals(".register"))
                    {
                        Object obj = fromClientObject.readObject();
                        Users user = (Users) obj;
                        server.registerUsers(user);
                    }

                    //If clients sends .findUser command then see if user exists in DB
                    if (input.equals(".findUser"))
                    {
                        //Read object from client
                        Object obj = fromClientObject.readObject();
                        Users user = (Users) obj;

                        //Create a pair and find the user
                        Pair<Boolean,Users> findUsers;
                        findUsers = server.findUsers(user); //This checks if the user exists and returns true or false

                        if(findUsers.getFirst())
                        {
                            toClientObject.writeUTF("True");
                            toClientObject.flush();

                            toClientObject.writeObject(findUsers.getSecond()); //Send the found user object to the client
                            toClientObject.flush();
                        }
                        else
                        {
                            toClientObject.writeUTF("false");
                            toClientObject.flush();
                        }
                    }
                }
            }
        }
        catch (IOException | ClassNotFoundException e)
        {
            e.printStackTrace();
        }

I've also tried using Scanner to receive the String and a seperate ObjectInputStream to receive the object but to no avail.

Below is how the client receives the string and object sent from the server as-well as how it sends information to the server

try(Socket socket = new Socket(host, portNumber);
    ObjectInputStream fromServerObject = new ObjectInputStream(socket.getInputStream());
    ObjectOutputStream toServerObject  = new ObjectOutputStream(socket.getOutputStream()))
    {
        Thread.sleep(1000);

        //Setup I/O
        toServerObject.writeUTF(code); //This is the string
        toServerObject.flush();

        toServerObject.writeObject(user); //This is a serialised object
        toServerObject.flush();


        if (code.equals(".findUser"))
        {
            String input = fromServerObject.readUTF();
            Users readUser = (Users) fromServerObject.readObject();

            if (input.equals("True"))
            {
                updateMessage("True");
                updateValue(readUser);
            } else if (input.equals("false"))
            {
                updateMessage("False");
            }
        } else
        {
            updateMessage("True");
        }
    }
    catch (IOException e)
    {
        System.err.println("Fatal Connection error!");
        e.printStackTrace();
        updateMessage("Failed");
    }
    return null;

Any ideas as to how to circumvent this? I was thinking about making separate functions to write a message/receive and a separate to write and receive and object but didn't wan't to attempt it without getting input on my current implementation.

score 0 · Accepted Answer · answered Apr 04 '18 at 17:42

The ordering of the streams seems to what solved the issue as explained here

The server is meant to receive then send and so it would be

ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
ObjectInputStream in = new ObjectInputStream(socket.getInputStream());

whereas the client is meant to send then receive so the order would be the reverse

Send objects and strings over socket

1 Answers1