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 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.
Lesson: Java Web Start
Java Web Start software provides the power to launch full-featured applications with a single click. Users can download and launch applications, such as a complete spreadsheet program or an Internet chat client, without going through lengthy installation procedures.
With Java Web Start software, users can launch a Java application by clicking a link in a web page. The link points to a Java Network Launch Protocol (JNLP) file, which instructs Java Web Start software to download, cache, and run the application.
Java Web Start software provides Java developers and users with many deployment advantages:
- With Java Web Start software, you can place a single Java application on a web server for deployment to a wide variety of platforms, including Windows, Linux, and Solaris.
- Java Web Start software supports multiple, simultaneous versions of the Java platform. An application can request a specific version of the Java Runtime Environment (JRE) software without conflicting with the needs of other applications.
- Users can create a desktop shortcut to launch a Java Web Start application outside a browser.
- Java Web Start software takes advantage of the inherent security of the Java platform. By default, applications have restricted access to local disk and network resources.
- Applications launched with Java Web Start software are cached locally for improved performance.
- Updates to a Java Web Start application are automatically downloaded when the application is run standalone from the user’s desktop.
Java Web Start software is installed as part of the JRE software. Users do not have to install Java Web Start software separately or perform additional tasks to use Java Web Start applications.
Additional References
This lesson is intended to get you started with Java Web Start technology and does not include all available documentation. For more information about Java Web Start technology, see the following: