Institute of Information Science - University of Miskolc

Let's create a group Chat thick client application using Java-RMI technology.

Create two projects in a Java IDE for the client and server respectively. The following interaction diagram illustrates the conceptual operation.

We can create another diagram to demonstrate the operation:

• ChatUI is the user interface, which directly communicates with ChatClient.
• ChatClient is the client-side logic, implementing the IChatClient interface.
• Java RMI Registry serves for resolving service names, used by ChatClient to access the IChatServer interface.
• IChatServer is the interface through which ChatClient communicates with ChatServer.
• ChatServer is the server-side logic, implementing the IChatServer interface.
• Client List is the list of connected clients on the server.
• User Interface represents the user interface components interacting with the user.

This diagram shows the system's component connectivity and communication structure, including the interactions between client and server.

1.) IChatClient

  import java.rmi.Remote;
  import java.rmi.RemoteException;
  
  public interface IChatClient extends Remote {
        public void tell(String name) throws RemoteException;
        public String getName() throws RemoteException;
  }

2.) IChatServer

  import java.rmi.Remote;
  import java.rmi.RemoteException;
  import java.util.ArrayList;
  
  public interface IChatServer extends Remote {
      public boolean login(IChatClient client) throws RemoteException;
  
      public void publish(String s) throws RemoteException;
  
      public ArrayList<IChatClient> getConnected() throws RemoteException;
  }

3.) ChatServer

  import java.rmi.RemoteException;
  import java.rmi.server.UnicastRemoteObject;
  import java.util.ArrayList;
  
  public class ChatServer extends UnicastRemoteObject implements IChatServer {
      private static final long serialVersionUID = 4705993250126188735L;
      private ArrayList<IChatClient> v = new ArrayList<IChatClient>();
  
      public ChatServer() throws RemoteException {
      }
  
      public boolean login(IChatClient client) throws RemoteException {
          System.out.println(client.getName() + " got connected....");
          client.tell("You're connected");
          publish(client.getName() + " connected.");
          v.add(client);
          return true;
      }
  
      public void publish(String s) throws RemoteException {
          System.out.println(s);
          for (int i = 0; i < v.size(); i++) {
              try {
                  IChatClient tmp = (IChatClient) v.get(i);
                  tmp.tell(s);
              } catch (Exception e) {
                  e.printStackTrace();
              }
          }
      }
  
      public ArrayList<IChatClient> getConnected() throws RemoteException {
          return v;
      }
  }

4.) StartServer

  import java.rmi.Naming;
  
  public class StartServer {
      public static void main(String[] args) {
          try {
              // System.setSecurityManager(new RMISecurityManager());
              java.rmi.registry.LocateRegistry.createRegistry(1099);
              IChatServer server = new ChatServer();
              Naming.rebind("rmi://localhost:1099/chatserver", server);
              System.out.println("Server ready.");
          } catch (Exception e) {
              e.printStackTrace();
          }
      }
  }

1.) ChatClient

  import java.rmi.RemoteException;
  import java.rmi.server.UnicastRemoteObject;
  
  public class ChatClient extends UnicastRemoteObject implements IChatClient {
      private String name;
      private ChatUI ui;
  
      public ChatClient(String n) throws RemoteException {
          name = n;
      }
  
      public void tell(String st) throws RemoteException {
          System.out.println(st);
          ui.writeMsg(st);
      }
  
      public String getName() throws RemoteException {
          return name;
      }
  
      public void setGUI(ChatUI t) {
          ui = t;
      }
  }

2.) ChatUI

  import java.awt.BorderLayout;
  import java.awt.GridLayout;
  import java.awt.event.ActionEvent;
  import java.awt.event.ActionListener;
  import java.rmi.Naming;
  import java.util.ArrayList;
  
  import javax.swing.DefaultListModel;
  import javax.swing.JButton;
  import javax.swing.JFrame;
  import javax.swing.JLabel;
  import javax.swing.JList;
  import javax.swing.JOptionPane;
  import javax.swing.JPanel;
  import javax.swing.JScrollPane;
  import javax.swing.JTextArea;
  import javax.swing.JTextField;
  import javax.swing.border.EmptyBorder;
  
  public class ChatUI {
      private ChatClient client;
      private IChatServer server;
  
      public void doConnect() {
          if (connect.getText().equals("Connect")) {
              if (name.getText().length() < 2) {
                  JOptionPane.showMessageDialog(frame, "You need to type a name.");
                  return;
              }
              if (ip.getText().length() < 2) {
                  JOptionPane.showMessageDialog(frame, "You need to type an IP.");
                  return;
              }
              try {
                  client = new ChatClient(name.getText());
                  client.setGUI(this);
                  server = (IChatServer) Naming.lookup("rmi://"+ ip.getText() +"/chatserver");
                  server.login(client);
                  updateUsers(server.getConnected());
                  connect.setText("Disconnect");
              } catch (Exception e) {
                  e.printStackTrace();
                  JOptionPane.showMessageDialog(frame, "ERROR, we couldn't connect....");
              }
          } else {
              updateUsers(null);
              connect.setText("Connect");
          }
      }
  
      public void sendText() {
          if (connect.getText().equals("Connect")) {
              JOptionPane.showMessageDialog(frame, "You need to connect first.");
              return;
          }
          String st = tf.getText();
          st = "[" + name.getText() + "] " + st;
          tf.setText("");
          // Remove if you are going to implement for remote invocation
          try {
              server.publish(st);
          } catch (Exception e) {
              e.printStackTrace();
          }
      }
  
      public void writeMsg(String st) {
          tx.setText(tx.getText() + "\n" + st);
      }
  
      public void updateUsers(ArrayList<IChatClient> users) {
          DefaultListModel<String> listModel = new DefaultListModel<String>();
          if (users != null)
              for (int i = 0; i < users.size(); i++) {
                  try {
                      String tmp = ((IChatClient) users.get(i)).getName();
                      listModel.addElement(tmp);
                  } catch (Exception e) {
                      e.printStackTrace();
                  }
              }
          list.setModel(listModel);
      }
  
      public static void main(String[] args) {
          System.out.println("Hello World !");
          ChatUI c = new ChatUI();
      }
  
      // User Interface code.
      public ChatUI() {
          frame = new JFrame("Group Chat");
          JPanel main = new JPanel();
          JPanel top = new JPanel();
          JPanel cn = new JPanel();
          JPanel bottom = new JPanel();
          ip = new JTextField();
          tf = new JTextField();
          name = new JTextField();
          tx = new JTextArea();
          connect = new JButton("Connect");
          JButton bt = new JButton("Send");
          list = new JList();
          main.setLayout(new BorderLayout(5, 5));
          top.setLayout(new GridLayout(1, 0, 5, 5));
          cn.setLayout(new BorderLayout(5, 5));
          bottom.setLayout(new BorderLayout(5, 5));
          top.add(new JLabel("Your name: "));
          top.add(name);
          top.add(new JLabel("Server Address: "));
          top.add(ip);
          top.add(connect);
          cn.add(new JScrollPane(tx), BorderLayout.CENTER);
          cn.add(list, BorderLayout.EAST);
          bottom.add(tf, BorderLayout.CENTER);
          bottom.add(bt, BorderLayout.EAST);
          main.add(top, BorderLayout.NORTH);
          main.add(cn, BorderLayout.CENTER);
          main.add(bottom, BorderLayout.SOUTH);
          main.setBorder(new EmptyBorder(10, 10, 10, 10));
          // Events
          connect.addActionListener(new ActionListener() {
              public void actionPerformed(ActionEvent e) {
                  doConnect();
              }
          });
          bt.addActionListener(new ActionListener() {
              public void actionPerformed(ActionEvent e) {
                  sendText();
              }
          });
          tf.addActionListener(new ActionListener() {
              public void actionPerformed(ActionEvent e) {
                  sendText();
              }
          });
          frame.setContentPane(main);
          frame.setSize(600, 600);
          frame.setVisible(true);
      }
  
      JTextArea tx;
      JTextField tf, ip, name;
      JButton connect;
      JList list;
      JFrame frame;
  }

Task 1: Implement functionality so that when new clients join, the existing ones receive the complete user list.