About Java Web Start and Java Clients

Java Web Start is a new application deployment technology created by Sun Microsystems, Inc. JDeveloper supports the creation of the XML-based JNLP (Java Network Launching Protocol) definition upon which the Java Web Start technology is based. With the Java Web Start Wizard in JDeveloper, you can set up applications and applets to be maintained on the web server, but downloaded and run on client machines.

Note: To launch applications and applets with Java Web Start in JDeveloper, you must download and install the Java Web Start software from Sun Microsystems at this web site http://java.sun.com/products/javawebstart/. Users of your application or applet will also be required to install the software on their machines.

Purpose of the Java Web Start Technology

Although Java Web Start and applets may appear like similar technologlies, there are several differences:

Unlike the applet approach to deploying web-centric Java applications, Java Web Start does not rely on the web browser to perform the downloading of the application JAR files. Instead, Java Web Start downloads the application resources after the Java Web Start JNLP descriptor is downloaded through the web browser. The JNLP descriptor causes Java Web Start to launch and perform the actual downloading.
While the user may experience the applet identically in Java Web Start, they are not tied to the web browser as they would be with applets. Once the application is running, the web browser can be closed, and the application continues to run in Java Web Start.

With the Java Web Start software installed once on the user's machine, individual users can run applications and applets simply by clicking on a web page link. If the application is not present on their computer, Java Web Start automatically downloads all necessary files from the web server where the application libraries reside. It then caches the files on the client computer so the application is always ready to be relaunched anytime either from an icon on your desktop or from the browser link. The most current version of the application is always presented to the user since Java Web Start performs updates as needed.

For more information on Java Web Start go to this Sun Microsystems web page:

http://java.sun.com/products/javawebstart/

Files Generated by the Java Web Start Wizard

Users can use Java Web Start to run applications and applets on client machines, while you maintain the application on the web server. To support Java Web Start and web server downloading, the Java Web Start Wizard generates these files:

The Java Network Launching Protocol (JNLP) definition required by Java Web Start to download and launch the application. The .jnlp file describes the archive files and whether it includes an applet or an application.
An HTML file that contains the URL to initiate the downloading from the web server to the client. Although HMTL file creation is optional, it is highly recommended unless you intend to create the file manually.

The Role of the Web Server in JDeveloper

JDeveloper provides an embedded-OC4J web server. You can use it to simulate the process of deploying the Web Application Archive and downloading for use with Java Web Start. JDeveloper follows the J2SE deployment profile conventions for archiving components that run on the client machine (simple archive) and components that are deployed to the web server (Web Application Archive).

Note: To learn how to use the keytool and jarsigner tools to digitally sign your applications and applets for security purposes, search for "Key and Certificate Management Tool" on the Java Web Start web site: http://java.sun.com/products/javawebstart/

You must follow this process to complete the Java Web Start setup:

Create a simple Java Archive (.jar) file that contains the application source files to be downloaded and run on the client machine.
Launch the Java Web Start wizard in JDeveloper to create the HTML and JNLP files that will enable the application or applet to be downloaded and run on the client machine.
Create a Web Application Archive (.war) file which you deploy to the web server. It will contain the contents of the public_html directory in your JDeveloper mywork folder: including, the JAR, HTML and JNLP files.

Note: You will not be required to deploy the application to use the JDeveloper-embedded web server. JDeveloper provides a default web.xml definition to locate the contents of the public_html directory in your JDeveloper mywork folder.

Once you have setup the web server, you can launch the Java Web Start software in JDeveloper using the generated .html file. Java Web Start relies on your web browser to download the components identified by the .jnlp file. Another definition in the .jnlp file determines whether it will run as an application or a secure applet. Once you have launched Java Web Start and the downloading is complete, you can close your web browser and continue to run the application or applet.