Java Web Start - Examples

Sandboxed demonstration of the methods of the BasicService (getCodeBase(), isOffline(), isWebBrowserSupported() & showDocument(URL)).

In Java 6+, a call to show another web start launch file (e.g. BasiceService.showDocument(another.jnlp)) will be handed directly to JavaWS, with no browser window appearing.

Sandboxed demonstration of the methods of the ClipboardService.

See the JWS - Lazy downloads page for further details and discussion.

Java web start (JWS) offers the installer-desc element to identify an installer/uninstaller for an application. The intent of the installer is to do any application set-up/pull-down that can not be handled by the standard JWS behaviour of caching the classes/resources at 1st launch, and clearing them at uninstall.

Two versions of this trivial application (a JLabel within a JFrame) are offered. The first will pop an 'End User Licence Agreement' before application launch, and it will appear either once (the user clicks 'OK') or as many times as the user wants if they cancel it. Once the user chooses to OK the EULA, the application will appear.

The second version also ensures the end user has a Java version suitable to call the uninstaller, which simply pops a JOptionPane that thanks the user for their patronage. Bug reports 6515728 & 6568950 refer.

The JNLP API provides services to allow even sandboxed applications to open and write to local files, with the specific permission of the end user.

If the application is trusted, a call to openFileDialog() (or equivalents) will go unchallenged and simply proceed to show a file chooser. Sandboxed applications, on the other hand, will invoke a trust dialog asking the user if they want to allow the program to access local files. The user can allow it (just once, or for the rest of that run), or cancel the request.

Note that the launch file prompts the user to associate file extension .zzz (simply a file type unlikely to clash with existing file associations) of content type text/sleepytime. The build file allows the file-type to be set at build time, see the build.xml in the distributable for details.

Java 1.5+ VM's should be able to provide a better user experience for sandboxed applications, in regards to 'double click-open' files. A 1.5+ VM comes complete with the ExtendedService, which allows us to open a FileContents object directly (without the file chooser), as soon as the user OK's that file.

This code has been mentioned on the Sun web-start forum under the title Example of using the JNLP file API *.

Caution: The FSS has a number of quirky aspects, see 6646622 & 6646617.

Sandboxed demonstration of the JNLPRandomAccessFile class of the web start API.

The Head'n'Tail application offers text areas in a split pane. The top text area shows the 'head' of any file the user chooses, while the lower text area displays the file's 'tail'. A combo box on top of the GUI determines the maximum number of bytes read and displayed (from 100-2000 bytes).

The JNLPRandomAccessFile instance provides methods that allow us to jump directly to the point near the end of the file from which to read the 'tail'. This represents a relatively trivial use of the JNLPRandomAccessFile - which also offers methods for reading and writing of Boolean, Byte, Float, Char, UTF, lines.. as well as moving around the file as needed - and so could represent an efficient way to access large data files.

This demo also uses FileOpenService & FileContents, examined in the FileOpen/SaveService example.

Demonstration of the methods of the PersistenceService.

The simple 'JotPad' application stores notes the user types in, as well as remembering the application's location, size, and PLAF.

Sandboxed demonstration of the PrintService.

This demo also uses FileOpenService & FileContents, examined in the FileOpen/SaveService example.

The SingleInstanceService ensures there is only one version of an application on-screen at any given moment. If the user opens the program while an instance is already on-screen, the application's notification method is called, and the developer gets to decide what action needs to be taken (such as opening a new editing tab with another file, or otherwise updating the parameters of the current instance).

This version simply alerts the user that new arguments have been received, and adds the time and arguments to the application's editing area.

This code has been mentioned on the Sun web-start forum under the title Example - using web-start SingleInstanceService *. It was also used as the test case in the bug report 6631056.