Java Web Start: Difference between revisions

Revision as of 18:01, 20 December 2006

Revision as of 07:31, 5 January 2007

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== Java Network Launching Protocol ==

'''Java Network Launching Protocol''' ('''JNLP''') is a closely-related concept that is often used interchangeably with the term "Web Start." It is the protocol, defined as an [[XML]] file format, that specifies how Java Web Start applications are startedlaunched. JNLP consists of a set of rules defining how exactly this launching mechanism should be implemented. JNLP files include information such as the ___location of the [[Jar (file format)|jar]] package file and the name of the main class for the application, in addition to any other parameters for the program. With a properly configured browser, JNLP files are passed to a Java Runtime Environment which in turn downloads the application onto the user's machine and starts executing it. JNLP was developed under the [[Java Community Process]] as JSR 56, which includes the original 1.0 release, the subsequent 1.5 maintenance release, and as of [[2006]], the pending 6.0 maintenance release. JNLP is free i.e. you don't have to pay anything to use it in your programs!

Important Web Start features include the ability to automatically download and install a JRE in the case where the user does not have Java installed, and for programmers to specify which JRE version is needed to run a given program. The user does not have to remain connected to the Internet to execute the downloaded programs, because they execute from a locally-maintained [[cache]]. Finally, automatic updates of the software from the Web are available when the user is connected to the Internet, thus easing the burden of deployment.

Anyone can reap the benefits provided by JNLP by simply installing a JNLP Client (most commonly Java Web Start). This Client Installation can be made automatic, so that the end users can see the client launcher automatically downloaded and installed before the Java application the first time they launch the latter.

JNLP works on a classic Client-Server scheme. The JNLP Client reads and executes the JNLP File (that is the XML file) eventually contacting a JNLP Server or some web server for help. THe JNLP Client runs locally on the client system whereas the server is implemented by some servlet and is used only for some advanced features of the protocol.

== Well-known Web Start applications ==