Overview

Java Web Start Technology

Java Web Start is a helper application that gets associated with a Web browser. When a user clicks on a link that points to a special launch file (JNLP file), it causes the browser to launch Java Web Start, which then automatically downloads, caches, and runs the given Java Technology-based application. The entire process is typically completed without requiring any user interaction, except for the initial single click.

From a technology standpoint, Java Web Start has a number of key benefits that make it an attractive platform to use for deploying applications:

Java Web Start is built exclusively to launch applications written to the Java(TM) Platform Standard Edition. Thus, a single application can be made available on a Web server and then deployed on a wide variety of platforms, including Windows 98/NT/2000/ME/XP, Linux, and the Solaris^TM Operating Environment. The Java platform has proven to be a very robust, productive, and expressive development platform, leading to a significant cost savings due to minimized development and testing costs.
Java Web Start supports multiple revisions of the Java(TM) Platform Standard Edition. Thus, an application can request a particular version of the platform it requires, such as Java SE^TM 1.5.0. Several applications can run at the same time on different platform revisions without causing conflicts, and Java Web Start can automatically download and install a revision of the platform if an application requests a version that is not installed on the client system.
Java Web Start allows applications to be launched independently of a Web browser. This can be used for off-line operation of an application, where launching through the browser is often inconvenient or impossible. The application can also be launched through desktop shortcuts, making launching the Web-deployed application similar to launching a native application.
Java Web Start takes advantage of the inherent security of the Java Platform. Applications are by default run in a protective environment (sandbox) with restricted access to local disk and network resources. It allows the user to safely run applications from sources that are not trusted.
Applications launched with Java Web Start are cached locally. Thus, an already-downloaded application is launched on par with a traditionally installed application.

The technology underlying Java Web Start is the Java^TM Network Launching Protocol & API (JNLP). This technology was developed via the Java Community Process (JCP). Java Web Start is the reference implementation (RI) for the JNLP specification. The JNLP technology defines, among other things, a standard file format that describes how to launch an application called a JNLP file.

Security

Java Web Start is built on top of the Java(TM) SE platform, which provides a comprehensive security architecture. Applications launched with Java Web Start will, by default, run in a restricted environment ("sandbox") with limited access to files and network. Thus, launching applications using Java Web Start maintains system security and integrity.

An application can request unrestricted access to your system. In this case, Java Web Start will display a Security Warning dialog when the application is launched for the first time. The security warning will show information about the vendor who developed the application. If you choose to trust the vendor, then the application will be launched. The information about the origin of the application is based on digital code signing.

Where to find Java Web Start

Java Web Start is included in the Java Runtime Environment available at http://java.sun.com. The JNLP specification can be found at JSR 56: Java Network Launching Protocol and API.

Using Java Web Start Software

Java Web Start allows you to launch Java-technology-based applications directly from the Web. An application can be launched in three different ways:

From a Web browser by clicking on a link.
From desktop icons or the Start Menu.
From the Java Cache Viewer

Regardless of which way is used, Java Web Start will connect back to the Web server each time an application is launched to check whether an updated version of the application is available.

Launching from a Web browser

Point your web browser to a page with a link to a jnlp application, and click on that link.

Some applications require extra privileges, such as access to your local hard disk. For these applications, a security dialog will pop up with information about the origin of the application based on who digitally signed the code. The application will run only if you decide to trust the vendor.

That is really all there is to using Java Web Start, but how does it work? The HTML links that launch the applications are, in fact, standard HTML links. However, instead of pointing to another Web page, they link to a special configuration file called a JNLP file. The Web browser examines the file extension and/or the MIME type of the file, and sees that it belongs to Java Web Start. It then launches Java Web Start with the downloaded JNLP file as an argument. Java Web Start proceeds with downloading, caching, and running the application as directed by the JNLP file.

Launching from desktop icons and the Start Menu (Microsoft Windows and Unix running GNOME 2.0+)

Java Web Start technology can automatically create shortcuts for your application on the desktop and in the Start Menu for Web-deployed applications developed with Java technology. You can use the Java Control Panel to control the shortcut settings. Shortcuts can also be added by using the Java Web Start Cache Viewer, using the install shortcut menu item.

Using Java Web Start Software Behind a Proxy Server/Firewall

Java Web Start software must be configured with the correct proxy settings in order to launch applications from outside your firewall. Java Web Start software will automatically try to detect the proxy settings from the default browser on your system (Internet Explorer or Netscape^TM browsers on Microsoft Windows, and Netscape browsers on the Solaris Operating Environment and Linux). Java Web Start technology supports most web proxy auto-configuration scripts. It can detect proxy settings in almost all environments.

You can also use the Java Web Start Control Panel to view or edit the proxy configuration. Refer to the Java Control Panel for more details.

Requirements

Desktop/Client requirements:

The client machine requires support for the Java Runtime Environment (JRE), version 1.3 or later. Java Web Start is available for Windows 98/NT/2000/ME/XP, the Solaris Operating Environment, and Linux.

Server requirements:

Applications can be deployed from any standard Web server. In order to use Java Web Start, the Web server must be configured with support for a new MIME type. See Setting Up the Web Site.