objectInputStream.readObject() throws exception java.io.OptionalDataException

Question

Can someone please resolve this issue. Using JDK 1.8, I am trying to build a very simple chat application in Java using Sockets. In my client class as soon as following line executes Message returnMessage = (Message) objectInputStream.readObject(); it throws exception. Exception in thread "main" java.io.OptionalDataException

I am writing only objects of type Message to the stream and reading objects of type Message, since i wrote once, i dont think i am doing anything wrong in reading them in sequence.

Q. Also please let me know what is the best way to debug this type of application, how to hit the breakpoint in server while running client ?

Client

package com.company;

import sun.misc.SharedSecrets;

import java.io.*;
import java.net.Socket;
import java.net.UnknownHostException;

public class Client {
    public static void main(String[] args) throws UnknownHostException, IOException, ClassNotFoundException{

            Socket socket = new Socket("localhost", Server.PORT);

            ObjectOutputStream objectOutputStream = new ObjectOutputStream(socket.getOutputStream());
            ObjectInputStream objectInputStream = new ObjectInputStream(socket.getInputStream());

            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
            String readerInput = bufferedReader.readLine();
            String[] readerInputTokens = readerInput.split("\u0020");

            if(readerInputTokens.length != 2) {
                System.out.println("Usage: Client <integer> <integer>");
            } else {
                Integer firstNumber = Integer.decode(readerInputTokens[0]);
                Integer secondNumber = Integer.decode(readerInputTokens[1]);

                Message message = new Message(firstNumber, secondNumber);

                objectOutputStream.writeObject(message);


                System.out.println("Reading Object .... ");
                Message returnMessage = (Message) objectInputStream.readObject();

                System.out.println(returnMessage.getResult());

                socket.close();
            }
    }

    public static boolean isInteger(String value) {
        boolean returnValue = true;
        try{Integer.parseInt(value);}
        catch (Exception ex){ returnValue = false; }
        return returnValue;
    }
}

Server

package com.company;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;


public class Server {
    public final static int PORT = 4446;
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        new Server().runServer();
    }

    public void runServer() throws IOException, ClassNotFoundException {

        ServerSocket serverSocket = new ServerSocket(PORT);
        System.out.println("Server up & ready for connections ...");

        // This while loop is necessary to make this server able to continuously in listning mode
        // So that whenever a client tries to connect, it let it connect.
        while (true){
            Socket socket = serverSocket.accept(); // Server is ready to accept connectiosn;.

            // Initialize Server Thread.
            new ServerThread(socket).start();
        }
    }
}

Sever Thread

package com.company;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;

public class ServerThread extends Thread {
    private Socket socket = null;
    ServerThread(Socket socket){
        this.socket = socket;
    }

    public void run() {

        try {

            ObjectOutputStream objectOutputStream = new ObjectOutputStream(socket.getOutputStream());
            objectOutputStream.writeChars("\n");
            objectOutputStream.flush();

            ObjectInputStream objectInputStream = new ObjectInputStream(socket.getInputStream());

            Message message = (Message) objectInputStream.readObject();
            multiplyNumbers(message);
            System.out.println("Writing: "+message.toString());
            objectOutputStream.writeObject(message);
            System.out.println("Message Written");
            socket.close();

        } catch( IOException ex) {
            ex.printStackTrace();

        } catch (ClassNotFoundException ex) {
            ex.printStackTrace();
        }
    }

    private void multiplyNumbers(Message message) {
        message.setResult(message.getFirstNumber().intValue() * message.getSecondNumber().intValue());
    }
}

Message Class

 package com.company;

import java.io.Serializable;

public class Message implements Serializable {
    private static final long serialVersionUID = -72233630512719664L;

    Integer firstNumber = null;
    Integer secondNumber = null;
    Integer result = null;

    public Message(Integer firstNumber, Integer secondNumber) {
        this.firstNumber = firstNumber;
        this.secondNumber = secondNumber;
    }

    public Integer getFirstNumber() {
        return this.firstNumber;
    }

    public Integer getSecondNumber() {
        return this.secondNumber;
    }

    public Integer getResult() {
        return this.result;
    }

    public void setResult(Integer result) {
        this.result = result;
    }

    @Override
    public String toString() {
        return "Message{" +
                "firstNumber=" + firstNumber +
                ", secondNumber=" + secondNumber +
                ", result=" + result +
                '}';
    }
}

Answer 1

 objectOutputStream.writeChars("\n");

Why are you writing a newline to an ObjectOutputStream? You're never reading it. Don't do that. Remove this wherever encountered.