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 ofJPanel
. Lay out your application's GUI components in the constructor of theMyTopJPanel
class. - Create a class called
MyApplication
that is a subclass of theJFrame
class. - In the
main
method of theMyApplication
class, instantiate theMyTopJPanel
class and set it as the content pane of theJFrame
.
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 Swing to learn more about using Swing GUI components.
Click the following Launch button to launch the Dynamic Tree Demo application.
Note: If you don't see the example running, you might need to enable the JavaScript interpreter in your browser so that the Deployment Toolkit script can function properly.
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.