Jump to content

Java Web Start

From Wikipedia, the free encyclopedia
This is an old revision of this page, as edited by Rawlogic (talk | contribs) at 20:12, 13 January 2009 (→Signed Web Start applications: - Publishers should sign the Web Start apps, not the end-users.). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.
Java Web Start, introduced in Java 2, allows provisioning applications over the Web by clicking a desktop icon or a link on a website.

In computing, Java Web Start (also known as JavaWS or as javaws), a framework developed by Sun Microsystems, allows users to start application software for the Java Platform directly from the Internet using a web browser. Unlike Java applets, Web Start applications do not run inside the browser, and the sandbox in which they run need not have as many restrictions, although this can be configured. Web Start has an advantage over applets in that it overcomes many compatibility problems with browsers' Java plugins and different JVM versions. On the other hand, Web Start programs cannot communicate with the browser as easily as applets. To assist migration, users can also invoke a Java Applet as a Java Web Start application.

Web Start provides a series of classes in the javax.jnlp package which provide various services to the application. 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.

Sun introduced version 1.0 of Web Start in March 2001.[1] Since J2SE 1.4 Web Start comes as a default part of Java Runtime Environment (JRE) and computer administrators no longer have to install it separately.

Java Web Start resembles ClickOnce in the .NET framework.

Java Network Launching Protocol

Programmers often speak of the Java Network Launching Protocol (JNLP, a closely-related concept) interchangeably with the term "Web Start". The JNLP protocol, defined with an XML schema, specifies how to launch Java Web Start applications. JNLP consists of a set of rules defining how exactly to implement the launching mechanism. JNLP files include information such as the location of the jar package file and the name of the main class for the application, in addition to any other parameters for the program. 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 development of JNLP took place under the Java Community Process as JSR 56. It 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; developers need not pay a license fee in order to use it in 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 a given program needs in order to execute. The user does not have to remain connected to the Internet to execute the downloaded programs, because they execute from a locally-maintained cache. Updates of the software download from the Web are available when the user is connected to the Internet, thus easing the burden of deployment.

Any computer user can use JNLP by simply installing a JNLP client (most commonly Java Web Start). The client installation can occur automatically, so that the end users can see the client launcher downloading and installing before the Java application the first time they launch the latter.

JNLP works in a similar fashion to how HTTP/HTML works for the web. For rendering a HTML webpage, after the user clicks on a weblink, the browser submits a URL to a webserver, which replies with a HTML file. The browser then requests the resources refered to by this file (images, css), and finally renders the page once enough information has been retrieved. The page is usually rendered before all resources have been retrieved; some resources not critical to the layout of the page (images), can be retrieved afterwords or on request should 'Load Images Automatically' browser setting be unset.

This process is mirrored for JNLP; in the same way that a Web browser renders a webpage, a JNLP client 'renders' a Java app. After the user clicks on a weblink the browser submits a URL to a webserver, which replies with a JNLP file (instead of a HTML file) for the application. This file is parsed by the JNLP client, which then requests the resources referenced by this(jar files), and then launches the application once all required resources have been retrieved. Some resources can be marked 'lazy' within the JNLP file, which informs the JNLP client that the application does not need those resources to start, but can be retrieved later on when/if the application requests them.

Signed Web Start applications

By default, Java Web Start applications run restricted, which means that they do not have access to some system resources such as local files. But publishers can remove these restrictions by signing their Web Start applications with the jarsigner tool that comes with the JDK.

Well-known applications

See also

References

  1. ^ Java Web Start 1.0 press release
Retrieved from "https://en.wikipedia.org/w/index.php?title=Java_Web_Start&oldid=263877092"