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Where to Start with Java Web Start

  • July 8, 2009
  • By Sridhar M S
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Ever wondered how to deliver the latest version of a Java application client to a user without the user having to install it? Ever wondered how to launch Java application clients without installing them? The answer is Java Web Start, the deployment solution for Java-based applications. Web Start eliminates the tedious procedures for upgrading existing application versions, and it can ensure that your users are running the latest version.

For the user, invoking Java Web Start is as simple as clicking on the link or typing a URL in a browser. Web Start takes control of the environment and ensures the application is up to date, and the user doesn't have to know about any of the background activities. Based on the Java Network Launching Protocol (JNLP), Web Start lets you specify the version of Java that users must have installed before they can execute the application.

This article provides the basics for you to begin using Java Web Start to deploy your Java application clients.

How Does Web Start Work?

To a provide Web Start-based application, you use a web server. The web server needs to be configured for the MIME type of .jnlp files. That is, the files of type .jnlp must to be set as application/x-java-jnlp-file. This setup invokes Java Web Start whenever a file of type .jnlp is provided to the URL. The web server also must have access to all the files that will be served using Java Web Start. This allows the web server to serve the application without any hassles.

You start Java Web Start by invoking a .jnlp file, which contains a list of supported entities that are required for the application to run. The specified resources will be downloaded to the user's machine first and then executed based on information such as which is the main class, and so on.

For versioning, Java Web Start verifies that the specified files located on the server match those that reside in the user's PC, and if it finds an updated file on the server, it downloads it to the user's PC before starting the application. When the application is launched for the first time, Java Web Start downloads all the related resources from the server and then starts the application.

Using Java Web Start preserves the richness of the application client, as Web Start downloads the complete application client onto the user's machine and launches it using the JRE available on that machine. Generally, this setup provides superior richness to web applications. Of course, there are exceptions.





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