Java Version Checker Applet

Introduction

Applet Parameters
Deployment Options Comparison
JRE check options

Embedded in applet page
Redirect to applet page

Version History
See Also

The VersionCheck applet checks for a specific Java major release & if not available, redirects the user to another page. The redirect page might be a page of your own, or Sun's download page. VersionCheck represents an alternative to Sun's deployJava.js, or the older style HTMLconverter.

VersionCheck will work even if JavaScript is disabled.

Applet Parameters

The applet parameters are..

<param name='targetVersion' value='1.6'> The version of the JRE required for applets on this page (or the applet page).
<param name='redirect' value='oldjava.html'> A page to show if the required JRE is not installed.
<param name='applet' value='ourapplet.html'> (Optional) An applet page to go to, if successful. Use this form to avoid having to embed the version checking applet directly in every applet page that requires versioning.
<param name='bouncer' value='bouncer.html'> (Optional) A page via which to direct offsite URLs. It is a good idea to implement this if allowing the applet to be scripted based on the URL query parameters.

Deployment Options Comparison

This table summarises the effects of using VersionCheck with or without an applet parameter.

Deployment aspect	No applet parameter	With applet parameter
Jumps to applet page	1	2
Applet page breaks 'back' button	false	true
Jumps to redirect page	2	2
Redirect page breaks 'back' button	true	true

JRE check options

Embedded in applet page

Use this form for an applet that has the version checker embedded in the page. Used this way, the client goes directly to the applet page (the 'back button is not broken') but is sent to the redirect page if insufficient Java is available to run the main applet (at which point, the 'back button is broken').

An example applet element for using the embedded form of the CheckVersion applet..

<APPLET
  CODE='org.pscode.tool.applet.VersionCheck'
  ARCHIVE='lib/vc.jar'
  ALT='Enable Java to proceed'
  WIDTH='200'
  HEIGHT='30'>
<param name='targetVersion' value='1.6'>
<param name='redirect' value='http://www.java.com/'>
This applet requires the Java Plug-In available from
<a href='http://www.java.com/'>www.java.com</a>.
</APPLET>

Redirect to applet page

Use this form to bounce the version checker to an applet in another page, should the end user have the required java. Used this way, the 'back button is broken' for both the applet page and the redirect page.

Further, search engines are not going to detect this type of link to an applet page, the page will be invisible to them (unless there is also a direct HTML link). Of course, if the only interesting thing on the page is the applet, search engines will not document much besides the page meta tags and title in any case. Java binaries are not 'search engine friendly'.

An example applet element for using the redirect form of the CheckVersion applet..

<APPLET
  CODE='org.pscode.tool.applet.VersionCheck'
  ARCHIVE='lib/vc.jar'
  ALT='Enable Java to proceed'
  WIDTH='200'
  HEIGHT='30'>
<param name='targetVersion' value='1.6'>
<param name='redirect' value='oldjava.html'>
<param name='applet' value='applet.html'>
This applet requires the Java Plug-In available from
<a href='http://www.java.com/'>www.java.com</a>.
</APPLET>

Version History

Version 1.0. 2008-07-12
- Included functionality to parse the query parameters of the page URL and use them to override (in most cases*) the applet parameters written in the page. To do this we add a script dependency, using JavaScript to parse the URL parameters and write the applet element. This might be done using a servlet, but we thought it beneficial to show how to do it for a plain old web page. E.G.
  - http://pscode.org/check.html?ver=1.6&applet=http://rabbitbrush.frazmtn.com/pong2.html Would check the user browser is running 1.6 or better, then refer it back to the applet page at frazmtn.com (a 'Pong' game). If it is running 1.5 or less, they will be directed to the default page defined in the applet parameters.
  - http://pscode.org/check.html?ver=2.5&redirect=http://www.java.com&applet=applet1.html Would check the user browser is running 2.5 or better, then refer it back to an applet page on this site. If it is running 2.4 or less, they will be directed to Sun. This link currently demonstrates the 'bouncer' page, since Java 1.6 is the current version and 1.7 is only available in beta builds.
- Added some very basic functionality to decode URL Encoded data. This was directly to support URL parsing. Most of Java's functionality to encode/decode URLs seems to have been introduced in Java 1.2 - so we go for a simplistic, home rolled version.
- Added a bouncer attribute as a local page to show before shifting a client browser 'off-site'. The page gets the destination URL added as a query parameter. Since so much of the applet is now configurable by URL, it opens the checker page to be used by 3rd party sites. That is - the checker page is used coming from links on the 3rd party site, and navigating back to the 3rd party site. The bouncer attribute allows you to put another page between the versioning applet, and returning to the final destination. This leaves it up to you what to do with that final link (and possibly the user's attention for a few moments). * The bouncer attribute is one that cannot be overriden in the URL!
Version 1.0-beta. 2008-07-05 SDN Share code - applet entirely rewritten.
- Class changed from the (default package) JavaVersionApplet to org.pscode.tool.applet.VersionCheck.
- Converted from using class availability to determine version, to parsing it from the java.version system property. This represents a fundamental improvement to the applet in that it no longer needs to be recompiled for each new release.
- Introduced dialog to provide user with messages, in case this is a very small applet running in a browser with no status line.
- URL construction simplified (within the code).
- Introduced fail-safe dialog message on failure to showDocument().
- Introduced the applet attribute to specify an applet web page to redirect to if successful. This allows us to have one page (with dynamically generated parameters) containing the version checking applet, to redirect to any number of applet pages that require version checking.
- Dropped all support for the target attribute of the redirecting URLs. Specifying targets has become more problematic and contentious over time.
Version 0.2 works on Win2K for the browsers mentioned above. Still untested in browsers on Mac, Linux, Unix, Solaris...
Version 0.1 works for IE 5, Mozilla 1.3a, NN 6.2 on Win2K. It fails for Opera 6.0, no redirect happens for JRE 1.5. As yet untested in browsers on Mac, Linux, Unix, Solaris...
The beta version had a faulty call to a method introduced in the 1.2 JRE