Unable to connect RMI client to host, unmarshalexception caused by eofexception

Question

I have the following files open in netbeans.

server:

package server;

import java.rmi.*;
import java.rmi.registry.*;
import java.rmi.server.*;
import java.sql.*;

public class Server implements ServerInterface {

    private Connection con;
    private Statement st;

    public Server(String db, String username, String password) {
        try {
            con = DriverManager.getConnection(db, username, password);
            st = con.createStatement();
        } catch(Exception e) {
            System.out.println(e);
        }
    }

    public static void main(String[] args) {
        try {
            Server server = new Server("jdbc:mysql://localhost:3306/db", "root", "password");
            System.setSecurityManager(new RMISecurityManager());
            ServerInterface stub = (ServerInterface) UnicastRemoteObject.exportObject(server, 0);
            Registry registry = LocateRegistry.createRegistry(1099);
            registry.rebind("Server", stub);
        } catch (Exception e) {
            System.out.println(e);
        }
    }

    public boolean authenticate(String username, String password) {
        try {
            String query = "SELECT * FROM staff WHERE staff_id ='" + username + "' AND password = '" + password + "'";
            ResultSet rs = st.executeQuery(query);
            if(rs.next()) {
                return true;
            } else {
                return false;
            }
        } catch(Exception e) {
            System.out.println(e);
        }
        return false;
    }
}

client:

package client;

import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
import java.rmi.registry.*;

public class Client extends JFrame implements ActionListener {

    JFrame main;
    JPanel loginPanel;
    JPanel contentPanel;
    JButton horse;
    JButton staff;
    JButton loan;
    JButton treatment_record;
    JButton work_record;
    JButton contact;
    JButton loaner;
    JButton field_visit;
    JButton login;
    JTextField username;
    JPasswordField password;
    String usernameString;
    String passwordString;

    public Client() {

        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception e) {
            System.out.println(e);
        }

        loginPanel = new JPanel();
        contentPanel = new JPanel();
        login = new JButton("Login");
        username = new JTextField(20);
        password = new JPasswordField(20);
        horse = new JButton("Horses");
        staff = new JButton("Staff");
        loan = new JButton("Current Loans");
        treatment_record = new JButton("Treatment Records");
        work_record = new JButton("Work Records");
        contact = new JButton("Contacts");
        loaner = new JButton("Loaners");
        field_visit = new JButton("Field Visits");

        horse.addActionListener(this);
        staff.addActionListener(this);
        loan.addActionListener(this);
        treatment_record.addActionListener(this);
        work_record.addActionListener(this);
        contact.addActionListener(this);
        loaner.addActionListener(this);
        field_visit.addActionListener(this);
        login.addActionListener(this);

        loginPanel.add(new JLabel("Username"));
        loginPanel.add(username);
        loginPanel.add(new JLabel("Password"));
        loginPanel.add(password);
        loginPanel.add(login);
        contentPanel.add(horse);
        contentPanel.add(staff);
        contentPanel.add(loan);
        contentPanel.add(treatment_record);
        contentPanel.add(work_record);
        contentPanel.add(contact);
        contentPanel.add(loaner);
        contentPanel.add(field_visit);
        contentPanel.setLayout(new GridLayout(0, 3));
        loginPanel.setLayout(new GridLayout(0, 2));
        contentPanel.setSize(800, 600);

        this.setTitle("TRC Database");
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.setContentPane(loginPanel);
        this.setVisible(true);   
        this.pack();
    }

    public static void main(String[] args) {
        new Client();

        try {
            Registry registry = LocateRegistry.getRegistry();
            ServerInterface stub = (ServerInterface) registry.lookup("Server");
        } catch (Exception e) {
            System.out.println(e);
        }
    }

    public void actionPerformed(ActionEvent ae) {
        if (ae.getSource() == login) {
            usernameString = username.getText();
            passwordString = password.getText();
            JOptionPane.showMessageDialog(null, "Button pressed!");
        }
        this.revalidate();
        this.pack();
    }
}

client side stub:

package client;

import java.rmi.*;

public interface ServerInterface extends Remote {
    public boolean authenticate(String username, String password) throws RemoteException;
}

server side stub:

package server;

import java.rmi.*;

public interface ServerInterface extends Remote {
    public boolean authenticate(String username, String password) throws RemoteException;
}

The server class executes fine, but running the client class gives the following error:

java.rmi.UnmarshalException: Error unmarshaling return header; nested exception is: 
    java.io.EOFException

Stacktrace:

java.rmi.UnmarshalException: Error unmarshaling return header; nested exception is: 
    java.io.EOFException
    at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:227)
    at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:377)
    at sun.rmi.registry.RegistryImpl_Stub.lookup(Unknown Source)
    at client.Client.main(Client.java:88)
Caused by: java.io.EOFException
    at java.io.DataInputStream.readByte(DataInputStream.java:267)
    at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:213)
    ... 3 more

I've seen a lot of people having the same error message but I can't find any solutions posted to it. Can anyone here please help me?

Answer 1

This is usually caused by sandbox permission problems at the peer. Get rid of the security manager. You don't need it here.

Answer 2

Another reason might be that the objects you want to transfer are not really serializable. Unfortunately the server RMI does not log this by default. The best way to check this is on server side before returning the object:

  try {
     new ObjectOutputStream(new ByteArrayOutputStream()).writeObject(object);
  } catch (Exception e) {
     logger.error("serializable check failed", e);
  }