Java Class File Editor

Quite an interesting tool to work on Java class files.

"This is a tool to open Java class file binaries, view their internal structure, modify portions of it if required and save the class file back. It also generates readable reports similar to the javap utility. Easy to use Java Swing GUI. The user interface tries to display as much detail as possible and tries to present a structure as close as the actual Java class file structure. At the same time ease of use and class file consistency while doing modifications is also stressed. For example, when a method is deleted, the associated constant pool entry will also be deleted if it is no longer referenced. In built verifier checks changes before saving the file. This tool has been used by people learning Java class file internals. This tool has also been used to do quick modifications in class files when the source code is not available. "

Java Class File Editor - http://classeditor.sourceforge.net/

Laucher for Java desktop application

Launching my Java desktop application in windows environment just by mouse clicks, this was my requirement. In my normal approach, where in which I have an application jar file and a couple of other supporting libraries, the command line invoking was quite annoying. This is because I may use a .bat file, and running this will open up a window, and I don't really want all these to happen.
So I have started searching and ended up with evaluating Launch4j (http://launch4j.sourceforge.net/), a pretty good tool for my needmake a launcher application. This tool can be used to wrap applications on Windows, Linux, Mac OS X and Solaris and available under BSD license.

In my case, I was quite lucky, because all the required jar files (application and libraries), JRE etc are available in same location in all machines. So I have to just make the launcher .exe and distribute ...

(1) Make all libraries available (Say under folder c:), and lauch the Launch4j
(2) Fill in the required details under `Basic` tab.

(3) Fill in the details under the `Classpath` tab

(4) If we need to run the application as a single instance, provide the details under `Single instance` tab

(5) Specify any JRE related configurations under `JRE` tab

(6) Click on the Build Wrapper button from the top,

This will create a configuration file (xml) and an exe file which is going to be the launcher.

Tray Icon in Java 6

I am much biased to web applications, the reason is that the new approaches that emrges every day facinated me a lot. But I am interested in destop based application (think client) also. When considering a Java application, taking the adavantage of OS System Tray/ Task Bar was not so easy until Java 6. But the latest release helped developers to a great extend. Here I have gicen a small Java program that can do the wonder of System Tray utilization, thanks Java 6.

import java.awt.Image;
import java.awt.MenuItem;
import java.awt.PopupMenu;
import java.awt.SystemTray;
import java.awt.Toolkit;
import java.awt.TrayIcon;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.JOptionPane;

/**
* ApplicationExecuter
* @author Rajeev Nair
*/
public class ApplicationExecuter {

 /**
  * main method
  * @param args - any command line arguments
  */
 public static void main(String args[]){
  
  if (!SystemTray.isSupported()){  
   System.out.println("System tray not supported on this platform");  
   System.exit(1);
  } //end if
  
  try {
   doTrayStartUp();
  } catch(Exception exp){
   System.out.println("Exception occured while building the tray entry :(");  
   exp.printStackTrace();
  } //end exception
  
 } //end main
 
 /**
  * Creates a tray icon.
  * @return TrayIcon
  */
 private static TrayIcon createTrayIcon()  { 
  // I have used an absolute path for image here .. :(
       Image image = Toolkit.getDefaultToolkit().getImage("C:\\Apps\\Icons\\app.gif");  
       PopupMenu popup = createTrayMenu();  
       TrayIcon ti = new TrayIcon(image, "Example TrayIcon :)", popup);  
       ti.setImageAutoSize(true);  
       return ti;  
   } //end createTrayIcon
 
 /**
  * Creates a popup menu.
  * @return PopupMenu
  */
 private static PopupMenu createTrayMenu()  {
  // creating popup
  PopupMenu menu = new PopupMenu();
  
  // creating an entry element
  MenuItem aboutItem = new MenuItem("About Example App!!!");  
  aboutItem.addActionListener(new ActionListener(){
         public void actionPerformed(ActionEvent e)   {  
          JOptionPane.showMessageDialog(null, "Hello, :)",
                        "About Example App!!!", JOptionPane.INFORMATION_MESSAGE);
            }
       }); 
  // addding an entry to popup menu
       menu.add(aboutItem); 
      
       // adding a separator
       menu.addSeparator();
      
       // creating an entry element
       MenuItem exitItem = new MenuItem("Exit");  
       exitItem.addActionListener(new ActionListener(){
         public void actionPerformed(ActionEvent e)   {  
                System.exit(0);  
            }
       });
       // addding an entry to popup menu
       menu.add(exitItem);  
       return menu;  
      
   }  //end createTrayMenu
 
 
 /**
  * Building the tray entry
  * @throws Exception
  */
 private static void doTrayStartUp() throws Exception{
  
   SystemTray sysTray = SystemTray.getSystemTray();
   TrayIcon trayIcon = createTrayIcon();  
        sysTray.add(trayIcon);  
        trayIcon.displayMessage("Example App",  "Example App started", TrayIcon.MessageType.INFO);  
       
        // add mouse listners
        trayIcon.addMouseListener(new MouseListener(){
        public void mouseClicked(MouseEvent e) {}

   public void mouseEntered(MouseEvent e) {}

   public void mouseExited(MouseEvent e) {}

   public void mousePressed(MouseEvent e) {
    if(e.getButton() == 1){
     // if left button pressed
     JOptionPane.showMessageDialog(null, "You have pressed the left button of the mouse.",
                          "Example App!!!", JOptionPane.INFORMATION_MESSAGE);
    } //end if
   }

   public void mouseReleased(MouseEvent e) {}
        });
 } //end doTrayStartUp
}

Screen shots after running this program,

How to run tomact with custom JVM arguments

Two approaches we can consider to run tomact with custom JVM argument values,

1. In the console just before running the startup.bat file, run the following line with required arguments

SET JAVA_OPTS=%JAVA_OPTS% -D[key=value]

eg: SET JAVA_OPTS=%JAVA_OPTS% -Dproj_env=dev

2. Add the following line in catalina.bat file.

JAVA_OPTS=%JAVA_OPTS% -D[key=value]

eg: JAVA_OPTS=%JAVA_OPTS% -Dproj_env=dev

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Spring Spring Spring !!!

Those who want to get a quick glance of Spring container configuration, please follow the link given below. In this video Rod Johnson discusses about the Spring Framework. He explains philosophy behind Spring, configuring the Spring container, XML configuration, new XML configuration namespaces, Annotation-based configuration, automatic component annotation scanning, Spring JavaConfig, mixing configuration types, and Spring 2.5 new features.

http://www.infoq.com/presentations/johnson-configuring-spring


Voca (UK's largest payment processing engine), they have shown the real capability of Spring. We do need to really appreciate the challenges they have taken to achieve the milestones. Wonderful ... Running such a mission critical system extends really the scope of Spring.

http://www.infoq.com/presentations/qcon-voca-architecture-spring


Couple of outstanding tutorials from Willie Wheeler can be found in,

http://wheelersoftware.com/articles/spring-web-flow-2.0.html


Enjoy the feast :)
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