Distributing software across the Web in the tradition manner requires the user to find the installer on the Web, download the installer, locate the installer on the system, and then execute the installer. Once the installer is executed, it prompts for installation directories and installation options such as full, typical, or minimum. This is a time-consuming and complicated task, and one that must be repeated for each new version of the software.
By contrast, Web-deployed applications, such as your favorite HTML-based email client and calendar, auction sites, and so on, are a breeze to install and use. The Web browser has automated the entire process. There is no complicated download, setup, and configuration steps, and you are guaranteed to always be running the latest version.
Java Web Start technology provides the same benefits to full-featured applications as described above for HTML-based applications. Java Web Start technology is an application deployment solution for the Web. Using a full-featured application instead of an HTML-based client can have many benefits:
On each launch, Java Web Start checks the Web server to see if a new version of the application is available, and if so, automatically downloads and launches it. Thus, applications are automatically brought up to date. There is no complicated upgrade procedure.
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.
The Java Tutorials contain examples that can be launched with a single click of a mouse; see Java Web Start Development Examples and Using Swing Components: Examples. Try launching the different applications by clicking on the Launch links or buttons. The Web browser will launch Java Web Start, which will then download, cache, and execute the given application. You will notice that the second time you launch an application, it starts much more quickly since it is already present locally and does not need to be downloaded again.
Most of the demos on the page are just downloaded and executed without any user intervention. These applications run in a restricted environment in which they are prevented from accessing the local disk and network, and can be guaranteed not to install any viruses on your computer.
Some demos 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.
The Application Manager is a built-in part of the Java Web Start product. It lets you quickly and easily launch applications that have previously been launched by Java Web Start. It is a combination of a History menu and a Start/Programs menu for your Web deployed Java-technology-based applications. The Application Manager also allows you to see additional information about the applications, with links the applications' home pages.
You launch an application from the Application Manager by double clicking on the application icon or by clicking the launch button.
Another important feature of the Application Manager is the Preferences dialog which lets you examine and modify settings used by Java Web Start. For example, this includes tabs which allow you to:
The Application Manager is launched by either clicking on the Java Web Start icon on the desktop or in the Start Menu on Microsoft Windows. On the Solaris Operating Environment and Linux, it is launched by invoking the javaws command in the Java Web Start installation directory. The Application Manager can also be launched from a Web browser; click the following link to launch it:
Shortcuts can also be added and removed by using the Application Manager, using the Application/Create Shortcut, and using Application/Remove Shortcut menu item.
If the proxy setting cannot be automatically detected, then you will be prompted to specify the proxy settings the first time you use Java Web Start. Java Web Start will also prompt you for a user name and password required to access an authenticating proxy server. This user name and password will be stored for the current invocation of Java Web Start. However, at the time a newly invoked Java Virtual Machine, if accessing a secure web site, will prompt you for the user name and password since this information is stored within a Java Virtual Machine instance.
You can also use the Java Web Start Preferences panel to view or edit the proxy configuration. Launch the Application Manager, either by clicking on the icon on the desktop (Microsoft Windows), or type ./javaws in the Java Web Start installation directory (Solaris Operating Environment and Linux), and then select Edit/Preferences. If you are in an environment where access to the Web is through a proxy server, you are encouraged to use the Java Web Start Preferences panel to check that these are set-up correctly.
