Developing a Java Web Start Application

Software designed by using component-based architecture can easily be developed and deployed as a Java Web Start application. Consider the example of a Java Web Start application with a Swing-based graphical user interface (GUI). With component-based design, the GUI can be built with smaller building blocks or components. The following general steps are used to create an application's GUI:

• Create a MyTopJPanel class that is a subclass of JPanel. Lay out your application's GUI components in the constructor of the MyTopJPanel class.
• Create a class called MyApplication that is a subclass of the JFrame class.
• In the main method of the MyApplication class, instantiate the MyTopJPanel class and set it as the content pane of the JFrame.

The following sections explore these steps in greater detail by using the Dynamic Tree Demo application. If you are not familiar with Swing, see Creating a GUI with JFC/Swing to learn more about using Swing GUI components.

Click the following Launch button to launch the Dynamic Tree Demo application.

Creating the Top JPanel Class

Create a class that is a subclass of JPanel. This top JPanel acts as a container for all your other UI components. In the following example, the DynamicTreePanel class is the topmost JPanel. The constructor of the DynamicTreePanel class invokes other methods to create and lay out the UI controls properly.

public class DynamicTreePanel extends JPanel implements ActionListener {
    private int newNodeSuffix = 1;
    private static String ADD_COMMAND = "add";
    private static String REMOVE_COMMAND = "remove";
    private static String CLEAR_COMMAND = "clear";
    
    private DynamicTree treePanel;

    public DynamicTreePanel() {
        super(new BorderLayout());
        
        //Create the components.
        treePanel = new DynamicTree();
        populateTree(treePanel);

        JButton addButton = new JButton("Add");
        addButton.setActionCommand(ADD_COMMAND);
        addButton.addActionListener(this);
        
        JButton removeButton = new JButton("Remove");
        ....
        
        JButton clearButton = new JButton("Clear");
        ...
        
        //Lay everything out.
        treePanel.setPreferredSize(new Dimension(300, 150));
        add(treePanel, BorderLayout.CENTER);

        JPanel panel = new JPanel(new GridLayout(0,3));
        panel.add(addButton);
        panel.add(removeButton); 
        panel.add(clearButton);
        add(panel, BorderLayout.SOUTH);
    }
    ....
}

Creating the Application

For an application that has a Swing-based GUI, create a class that is a subclass of javax.swing.JFrame.

Instantiate your top JPanel class and set it as the content pane of the JFrame in the application's main method. The main method of the DynamicTreeApplication class invokes the createGUI method in the AWT Event Dispatcher thread.

package webstartComponentArch;

import javax.swing.JFrame;

public class DynamicTreeApplication extends JFrame {
    public static void main(String [] args) {
        DynamicTreeApplication app = new DynamicTreeApplication();
        app.createGUI();
    }

    private void createGUI() {
        //Create and set up the content pane.
        DynamicTreePanel newContentPane = new DynamicTreePanel();
        newContentPane.setOpaque(true); 
        setContentPane(newContentPane);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pack();
        setVisible(true);
    }    
}

Benefits of Separating Core Functionality From the Final Deployment Mechanism

Another way to create an application is to just remove the layer of abstraction (separate top JPanel) and lay out all the controls in the application's main method itself. The downside to creating the GUI directly in the application's main method is that it will be more difficult to deploy your functionality as an applet, if you choose to do so later.

In the Dynamic Tree Demo example, the core functionality is separated into the DynamicTreePanel class. It is now trivial to drop the DynamicTreePanel class into a JApplet and deploy it as an applet.

Hence, to preserve portability and keep deployment options open, follow component-based design as described in this topic.

Download source code for the Dynamic Tree Demo example to experiment further.