Java Web Start (JWS) and the underlying Java Network Launch Protocol (JNLP) enable Java application delivery from a standard Web server. The end user initiates application installation by clicking on an URL. If the Java Web Start engine is not present on the system, the user is prompted to download and install it. Once Java Web Start is in place, clicking on the same URL will initiate the application download and installation procedures. It may involve download and installation of the required version of the JRE and Optional Packages. Upon their successful completion, the application is launched. The application will be cached on the user's system so next time the user clicks on the same URL, the JWS engine will launch the local copy of the application from the cache, if it detects that the computer is offline or the application was not updated on the Web site.
Another important feature of JWS is its ability to run your application in asandbox - a restricted container based on Java security architecture. But, unlike an applet, your application can gain access to local system resources like the filesystem, printer and system clipboard using the JNLP API even if it comes from an untrusted environment, after prompting the user for confirmation.
Java Web Start is available for Windows, Linux, and Solaris, and is part of MacOS X since v10.1. There are also third-party implementations of the JNLP protocol, some of them also include tools that assist you in the creation and maintenance of JNLP packages.
That was the bright side. Now, what is not so good about JNLP? First off, for seamless operation both the browser and the Web server that hosts the JNLP-enabled application must support application/x-java-jnlp-file MIME type. Some hosting providers do not support it. Moreover, versioning and incremental updates require additional support from the Web server, which has to be implemented using servlets, cgi-bin scripts, etc.
On the client side, a major browser would be configured to recognize the above MIME type during installation of the JWS engine, but users of less popular browsers, such as Opera, may have to do that manually.
JNLP-enabling an application may involve minor changes in its code and (re)packaging it into a set of jar files.
Before J2SE 5.0, JWS had very little to offer in terms of desktop integration - all it could do was create a desktop icon and/or a Start Menu entry for the application. On Windows, the application will not show up in Add/Remove Programs, so end users would have to run the Java Web Start application manager in order to remove your application.
Finally, JWS user interface needs much polishing. As of J2SE 5.0, users still complain about ugly windows with incomprehensible messages.
To sum it up, JWS can be a viable option in a controlled environment, such as corporate intranet, but it is not ready for the consumer market, where you may be better off using
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