JAVA RMI : A Shared Whiteboard

[eclipt]

Hello

i just want to know how to compile this "java rmi" code of a shared whiteboard

and how could i'm implement/embed it in my website
this the code. for better explaination go through http://www.unix.org.ua/orelly/java-ent/dist/ch10_02.htm

Example 1: A Shared Whiteboard Client

package dcj.examples.Collaborative;

import dcj.util.Collaborative.*;
import java.awt.event.*;
import java.awt.*;
import java.util.Hashtable;
import java.util.Properties;
import java.io.IOException;
import java.rmi.RemoteException;

public class WhiteboardUser extends RMICollaboratorImpl
                            implements MouseListener, MouseMotionListener
{
  protected Hashtable lastPts = new Hashtable();
  protected Component whiteboard;
  protected Image buffer;

  public WhiteboardUser(String name, Color color, String host, String mname)
         throws RemoteException {
    super(name);
    Properties p = new Properties();
    p.put("host", host);
    p.put("mediatorName", mname);
    connect(p);
    getIdentity().setProperty("color", color);
    System.out.println("color = " + color.getRed()
                       + " " + color.getGreen() + " "
                       + color.getBlue());
    buildUI();
  }

  protected void buildUI() {
    Frame f = new Frame();
    GridBagLayout gridbag = new GridBagLayout();
    GridBagConstraints c = new GridBagConstraints();
    f.setLayout(gridbag);
    f.addNotify();
    c.fill = GridBagConstraints.BOTH;
    c.gridwidth = GridBagConstraints.REMAINDER;
    Canvas canvas1 = new java.awt.Canvas();
    canvas1.setSize(240,180);
    canvas1.setBackground(Color.white);
    gridbag.setConstraints(canvas1, c);
    f.add(canvas1);
    String name = null;
    try {
      name = getIdentity().getName();
    }
    catch (Exception e) {
      name = "unknown";
    }
    Label label1 = new java.awt.Label("Your name: " + name);
    label1.setSize(100,30);
    gridbag.setConstraints(label1, c);
    f.add(label1);
    f.setSize(240,210);
    f.show();
    whiteboard = canvas1;
    whiteboard.addMouseListener(this);
    whiteboard.addMouseMotionListener(this);
    buffer = whiteboard.createImage(f.getSize().width,
                                    f.getSize().height);
  }

  public void mousePressed(MouseEvent ev) {
    Point evPt = ev.getPoint();
    try {
      broadcast("start", evPt);
    }
    catch (Exception e) {}
  }

  public void mouseReleased(MouseEvent ev) {
    Point evPt = ev.getPoint();
    try {
      broadcast("end", evPt);
    }
    catch (Exception e) {}
  }

  public void mouseDragged(MouseEvent ev) {
    Point evPt = ev.getPoint();
    try {
      broadcast("drag", evPt);
    }
    catch (Exception e) {
    }
  }

  public void mouseExited(MouseEvent ev) {}
  public void mouseMoved(MouseEvent ev) {}
  public void mouseClicked(MouseEvent ev) {}
  public void mouseEntered(MouseEvent ev) {}

  public boolean notify(String tag, Object data, Identity src)
                 throws IOException, RemoteException {

    Color origColor = null;
    Color agentColor = null;
    Graphics gr = buffer.getGraphics();
    try {
      agentColor = (Color)src.getProperty("color");
      if (agentColor != null) {
        gr.setColor(agentColor);
      }
      else {
        System.out.println("No agent color available.");
      }
    }
    catch (Exception exc) {
      System.out.println("Exception while switching colors.");
      exc.printStackTrace();
    }

    if (tag.compareTo("start") == 0) {
      lastPts.put(src.getName(), data);
    }
    else if (tag.compareTo("drag") == 0) {
      Point lastPt = (Point)lastPts.get(src.getName());
      Point currPt = (Point)data;
      gr.drawLine(lastPt.x, lastPt.y, currPt.x, currPt.y);
      lastPts.put(src.getName(), data);
    }
    else if (tag.compareTo("end") == 0) {
      Point lastPt = (Point)lastPts.get(src.getName());
      Point currPt = (Point)data;
      gr.drawLine(lastPt.x, lastPt.y, currPt.x, currPt.y);
      lastPts.remove(src.getName());
    }

    whiteboard.getGraphics().drawImage(buffer, 0, 0, whiteboard);

    return true;
  }
}

Example 2: A Multithreaded Whiteboard Client

package dcj.examples.Collaborative;

import dcj.util.Collaborative.*;
import java.awt.event.*;
import java.awt.*;
import java.util.Hashtable;
import java.util.Properties;
import java.io.IOException;
import java.rmi.RemoteException;
import java.util.Vector;

public class ThreadedWhiteboardUser 
    extends RMICollaboratorImpl
    implements java.awt.event.MouseListener,
               java.awt.event.MouseMotionListener
{
  protected Hashtable lastPts = new Hashtable();
  protected Component whiteboard;
  protected Image buffer;
  protected CommHelper helper;

  public ThreadedWhiteboardUser(String name, Color color,
                                String host, String mname)
         throws RemoteException {
    super(name, host, mname);
    getIdentity().setProperty("color", color);
    buildUI();
    helper = new CommHelper(this);
    helper.start();
  }

  protected void buildUI() {
    Frame f = new Frame();
    GridBagLayout gridbag = new GridBagLayout();
    GridBagConstraints c = new GridBagConstraints();
    f.setLayout(gridbag);
    f.addNotify();
    c.fill = GridBagConstraints.BOTH;
    c.gridwidth = GridBagConstraints.REMAINDER;
    Canvas canvas1 = new java.awt.Canvas();
    canvas1.setSize(240,180);
    canvas1.setBackground(Color.white);
    gridbag.setConstraints(canvas1, c);
    f.add(canvas1);
    String name = null;
    try {
      name = getIdentity().getName();
    }
    catch (Exception e) {
      name = "unknown";
    }
    Label label1 = new java.awt.Label("Your name: " + name);
    label1.setSize(100,30);
    gridbag.setConstraints(label1, c);
    f.add(label1);
    f.setSize(240,210);
    f.show();
    whiteboard = canvas1;
    whiteboard.addMouseListener(this);
    whiteboard.addMouseMotionListener(this);
    buffer = whiteboard.createImage(f.getSize().width,
                                    f.getSize().height);
  }

  protected void nextLine(String agent, Point pt, Color c) {
    Graphics g = buffer.getGraphics();
    g.setColor(c);
    Point lastPt = (Point)lastPts.get(agent);
    g.drawLine(lastPt.x, lastPt.y, pt.x, pt.y);
    whiteboard.getGraphics().drawImage(buffer, 0, 0, whiteboard);
  }

  public void mousePressed(MouseEvent ev) {
    Point evPt = ev.getPoint();
    try {
      lastPts.put(getIdentity().getName(), evPt);
      CommHelper.addMsg("start", evPt);
    }
    catch (Exception e) {}
  }

  public void mouseReleased(MouseEvent ev) {
    Point evPt = ev.getPoint();
    try {
      nextLine(getIdentity().getName(), evPt,
               (Color)getIdentity().getProperty("color"));
      lastPts.remove(getIdentity().getName());
      helper.addMsg("end", evPt);
    }
    catch (Exception e) {}
  }

  public void mouseDragged(MouseEvent ev) {
    Point evPt = ev.getPoint();
    try {
      nextLine(getIdentity().getName(), evPt,
             (Color)getIdentity().getProperty("color"));
      lastPts.put(getIdentity().getName(), evPt);
      helper.addMsg("drag", evPt);
    }
    catch (Exception e) {}
  }

  public void mouseExited(MouseEvent ev) {}
  public void mouseMoved(MouseEvent ev) {}
  public void mouseClicked(MouseEvent ev) {}
  public void mouseEntered(MouseEvent ev) {}

  public boolean notify(String tag, Object data, Identity src)
                 throws IOException, RemoteException {

    // If this is our own event, ignore it since it's already been handled.
    if (src.getName().compareTo(getIdentity().getName()) == 0) {
      return true;
    }

    Color agentColor = null;
    try {
      agentColor = (Color)src.getProperty("color");
    }
    catch (Exception exc) {
      System.out.println("Exception while getting color.");
      exc.printStackTrace();
    }

    if (tag.compareTo("start") == 0) {
      // First point along a path, save it and continue
      lastPts.put(src.getName(), data);
    }
    else if (tag.compareTo("drag") == 0) {
      // Next point in a path, draw a line from the last
      // point to here, and save this point as the last point.
      nextLine(src.getName(), (Point)data, agentColor);
      lastPts.put(src.getName(), data);
    }
    else if (tag.compareTo("end") == 0) {
      // Last point in a path, so draw the line and remove
      // the last point.
      nextLine(src.getName(), (Point)data, agentColor);
      lastPts.remove(src.getName());
    }

    return true;
  }
}

if someone can help me to embed it in my website i'm really appreciate it.

[Christoph Dürr]

The main difficulty is to sign the applet, so the navigators allow the applet to open a TCP connection to the server. For this you need to create a jar file with jar, create a private/public keypair with keytool, and sign the applet with jarsigner. I have done this for a home made applet.

I hope that this late answer is still hopefull for you.