Java Web Start

The technology enables seamless version updating for globally distributed applications and greater control of memory allocation to the Java virtual machine.

IcedTea-Web provides an independent open source implementation of Java Web Start that is currently developed by the AdoptOpenJDK community, RedHat and Karakun AG, and which is bundled in some OpenJDK installers.

Web Start has an advantage over applets in that it overcomes many compatibility problems with browsers' Java plugins and different JVM versions.

Sun designed most of these services with the aim of allowing carefully controlled access to resources (such as files and the system clipboard) while restricting the application to authorized operations.

Since J2SE 1.4 Web Start comes as a default part of Java Runtime Environment (JRE) called javaws, computer administrators no longer have to install it separately.

Programmers often speak of the Java Network Launching Protocol (JNLP) interchangeably with the term "Web Start".

The JNLP protocol, defined with an XML schema, specifies how to launch Java Web Start applications.

A properly configured browser passes JNLP files to a Java Runtime Environment (JRE) which in turn downloads the application onto the user's machine and starts executing it.

The browser then requests the resources referred to by this file (images, css), and finally renders the page once it has received enough information.

The example below gives a simple JNLP file to launch the applet, specifying code base, source, main class and window size.

[7] Java Web Start has supported Pack200 since it first appeared, but initially this feature required server-side cooperation and a certain amount of expertise to set up.

By default, Java Web Start applications run "restricted", which means that they do not have access to some system resources such as local files.

[9] The tool includes all the functionality of IcedTea-Web and adds extended features, such as native installers for Mac OS, Windows, and Linux.