Java Web Start

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In computing, Java Web Start (also known as JavaWS , javaws or JAWS ) is a framework developed by Sun Microsystems (now Oracle) that allows users to launch application software for Java Platform directly from the Internet using a web browser. Some of the major benefits of this technology include unlimited version updates for globally distributed apps and greater memory allocation controls to Java virtual machines.

Video Java Web Start

Function

Unlike Java applets, the Web Start app does not run inside the browser. By default, they run in the same sandbox as the applet, with some minor extensions such as allowing to load and save files explicitly selected by the user through the file selection dialog. Only signed apps can be configured to have additional permissions.

Web Start has advantages over applets as it overcomes many compatibility issues with different Java browser plugins and JVM versions. The Web Start program is no longer an integral part of web pages, they are independent applications that run in separate frames.

Web Start can also launch unmodified applets packed in. Jar files, by writing the appropriate JNLP file. This file can also bypass the applet parameters. Such applets also run in separate frames. Applet launcher may not support some specific cases such as loading the class as a resource.

Like applets, Java Web Start is cross-platform.

In JDK9, Java applets are no longer used by Oracle with Java Web Start as the desired substitute.

Oracle will not include Java Web Start in Java SE 11 (18.9 LTS) and later. Developers need to transition to other deployment technologies such as jlink.

Maps Java Web Start

Implementation

The developer sets up a custom XML file with the JNLP extension. This file describes the application requirements, code location, parameters, and additional permissions (if any). The browser downloads this file like the others and (following its MIME type, application/x-java-jnlp-file ) opens it with the Web Start tool. The Web Start Tool downloads all necessary resources and launches the app.

Java Web Start provides a series of classes in the javax.jnlp package that provides various services to the application. Sun designed most of these services in order to allow careful controlled access to resources (such as file and system clipboard) while restricting applications to authorized operations.

Sun introduced version 1.0 Web Start in March 2001, while 64-bit Windows support was added only in Java 6 (slower than 64-bit Java was first available). Since J2SE 1.4 Web Start comes as a default part of the Java Runtime Environment (JRE) called javaws , the computer administrator does not need to install it separately.

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Programmers often talk about Java Network Launching Protocol ( JNLP ) interchangeably with the term "Web Start". The JNLP protocol, which is defined by an XML schema, determines how to launch Java Web Start applications. JNLP consists of a set of rules that define how exactly applying the launch 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 other parameters for the program. A properly configured browser sends a JNLP file to the Java Runtime Environment (JRE) which in turn downloads the app to a user's computer and starts executing it. JNLP development takes place under the Java Community Process as JSR 56. This includes the original 1.0 release, the next 1.5 maintenance release, and in 2006, the delayed 6.0 maintenance release.

Essential Web Start features include the ability to automatically download and install JRE in cases where users do not have Java installed, and for programmers to determine which version of JRE is required for certain programs to be executed. Users do not have to stay connected to the Internet to run downloaded programs, because they execute from locally managed cache. Software download updates from the Web and become available when the user has a connection to the Internet, thereby reducing the burden of deployment.

Any computer user can use JNLP just by installing the JNLP client (most commonly Java Web Start). Installation can happen automatically so the end user sees the client launcher downloading and installing the Java application when it first starts up.

JNLP works in a way similar to how HTTP/HTML works for the web. To render an HTML webpage, after a user clicks on a web link, the browser sends the URL to the web server, which replies with the HTML file. The browser then requests the resources referenced by this file (image, css), and finally renders the page after receiving enough information. Page rendering usually starts before all resources are downloaded; some unimportant resources for page layout (like images) can be followed afterwards.

JNLP reflects this process; in the same way as Web browsers render web pages, JNLP clients "render" Java applications. After the user clicks on the web link, the browser sends the URL to the web server, which replies with a JNLP file (not an HTML file) for the app. The JNLP client parses this file, requests the specified resource (jar file), waits to extract all necessary resources, and then launches the app. The JNLP file can list resources as "lazy," which tells JNLP clients that the app does not need those resources to start, but can retrieve them later when/if the app requests them.

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Example

The example below provides a simple JNLP file to launch the applet, specifying the code base, source, main class and window size. The file contains all the necessary references and enough to launch the app. Since no permissions are requested, the code will run in a sandbox. JNLP also states that this app can run offline (if it is cached) and should be updated as a background process.

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Compression Pack200

To reduce the size of Java Web Start applications Sun Microsystems introduced a compression system called Pack200 in Java 1.5.0. It can compress large jar files to one-nine of their original size if they contain only Java classes.

Java Web Start has supported Pack200 since it first appeared, but initially this feature requires server side collaboration and a certain amount of expertise to set up. When Sun introduced Java SE 6u10, Pack200 support became available without requiring special server support. An application designer can enable or disable this feature in a JNLP file.

On a slow connection, Pack200 provides improved performance in application start time and download time.

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signed Web Start App

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

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Alternative

The open-source IcedTea project provides an alternative JNLP implementation on IcedTea-Web .

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Important apps

• ArgoUML - UML diagramming app.
• CrossFTP - FTP client and server.
• Elluminate Live - a web conferencing program/virtual class.
• Ganymede - GPL licensed network directory management system
• Genie Workbench - a set of film production automation tools.
• Genevestigator, machine access to a curated bioinformatics database.
• Jake2 - A Java port from Quake 2.
• JOSM - OpenStreetMap Java Editor.
• JabRef reference management software that uses BibTeX as the original format
• muCommander File manager and Norton Commander are cloned with SSH and ftp features
• PoxNora - 3/4 perspective, turn based strategy, card game collection.
• Wurm Online - Massive Multiplayer 3D Online Simulator.
• yEd - graphics editor and diagram.

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See also

• Java applets, other Java application deployment technologies.
• Zero Install, a similar system that works for non-Java applications.
• Similar template ClickOnce, Microsoft.NET.

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References

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External links

• Java Web Start product page
• Java Web Start and JNLP in Curlie (based on DMOZ)
• Deploy Software with JNLP and Java Web Start
• Java Web Start Developer Guide (6.0)
• JSR 56: Java Network Launching Protocol and API
• Java Web Start Tutorial
• Get started with Java Web Start

Implementation of JNLP apart from Sun's reference implementation:

• Netx
• IcedTea-Web (based on Netx)
• OpenJNLP
• xito

Source of the article : Wikipedia