JRE version check?

Hi,
I want put restriction on lower version of JRE's.
Now I'm checking this in following ways.
           String version = System.getProperty("java.version");
            if ((version.indexOf("1.4") == -1) && (version.indexOf("1.5") == -1))
                  //Show error that inproper JRE version and return;
            }But I want to put restriction on only lower versions of 1.4 JRE, not on upper versions like 1.6.
How to achieve this?
Thanks in advance,
Vikas

As you suggested we can compile source code with 1.5 or 1.6 which won't run with 1.4.
But at the time of application invocation I want to show msg that, this application will not work with JRE 1.4
So I want put generic check for all lower versions like if version is lower than 1.5 show error msg.
Thanks,
Vikas

Similar Messages

Version check of JRE in app

Hi,
I want my application(not web-based or whatever) to know which version of JRE the client is using.
The thing is, I know it's with System.getProperty("java.version"), but I want to compare it with another version string in the application. The user JRE version must be equal or greater than the version.
For ex: if the application was build with 1.4.0_01 and the user has 1.4.1_01, it must be accepted, but not if it's 1.3.x or whatever.
I've done a temporary method with a string tokenizer to evaluate each number and see if it's up to date, but is there a method or utility already there that checks if the version is equal or better?
Thx
Frank

i just have the same kind of problem. even more so, since i noticed that there are possibly more non-numeric characters in the version string, like "1.4.0-beta3", so even using a StringTokenizer splitting the string by the "." and "_" characters (like i think you do, from the example in your posting), the last part would cause a NumberFormatException in many cases.
of course you could include the "-" character in the tokenizer and drop the last token, but you can never be sure if there won't be version strings like "1.5.2b" or such in the future. a workaround here would be taking each character from the token, check if it's a number, add it to another string if so, or stop if it's a non-numeric character or the end of the string. then you could transform the constructed string into an integer and compare it to the corresponding part of the required version.
however, this seems to be quite a lot of not too elegant trickery which i'm not even sure will work in all cases, and it's definitely too much work for a simple version check. anyway, i haven't found any other way yet, too :/ if anyone knows, please let me know...

Version Checking Methods for JRE

Hi,
I am trying to ascertain how the version checking mechanisms for JRE interoperate. I am aware of 2 methods that Java/JRE uses to check the Client Version JRE
Method 1 – Non Static Version Checking on the JRE Client Side
Method 2 – Class ID Version Checking on the Web Server Side
Q1. If a JRE Client connects to a Web Server that requires a specific version of JRE, then the client pc will be prompted to download that JRE version ?
Q2. However if the client already has a later JRE version installed and Non Static Versioning is enabled on the client, then the later JRE version will be used ? I presume in this case the client is not prompted to download JRE ?
Q3. Alternatively if the appsweb.cfg on the Web Server is using a Family CLSID ( or even a Dynamic CLSID for that matter ) and the Client already has installed a JRE version in that class, again I presume the Client will use this and the client will not be prompted to download JRE ?
Q4. Does anyone know where the latest Class Id’s for the various JRE versions are listed ? Oracle Note 290807.1 seems to list them. However the link it has to the latest JRE version points you to JRE 1.8.0_40, yet the Class Ids that the same note lists, does not go as far as that version ( it seems to only list up to JRE 1.8.0_31 ). I presume you could guess the Clas Id for Update 40, given the entries for the other versions i.e.
clsid : CAFEEFAC-0018-000-0040-ABCDEFFEBCBA
sun_plugin_version=1.8.0_40
Is the above correct ?
Any advice greatly appreciated,
Jim

Sounds exactly like a dns timeout issue.

I have been getting java.lang.ClassNotFoundException: ZeroApplet.class and java.lang.ClassNotFoundException: JavaToJS.class crashes with JRE version 1.6.0_26-b03-384-10M3425 VM executing a Java Applet. Is Apple aware of this problem? No longer supported?

My web page uses a Java Applet to allow my visitors to replay chess games; the Chess Viewer Deluxe applet was written by Nikolai Pilafov some time ago and has been working properly for some time (until recently). I don't monitor this part of my site regularly so I am not sure when it began to fail. On his web site [http://chesstuff.blogspot.com/2008/11/chess-viewer-deluxe.html] he has a link to check LiveConnect object functionality (which fails for OBJECT tags). His recommendation is to "seek platform specific support which might be available from the JRE developers for your platform".
I have been getting java.lang.ClassNotFoundException: ZeroApplet.class and java.lang.ClassNotFoundException: JavaToJS.class crashes with JRE version 1.6.0_26-b03-384-10M3425 VM executing a Java Applet. Until I checked the LiveConnect object functionality, I was unable to identify the source of the console error messages. This does seem to be the smoking gun.
Is Apple aware of this problem? Are these classes no longer supported? Has anyone else had this problem? You can attempt to recreate the problem locally by going to my web page: http://donsmallidge.com/DonSmallidgeChess.html
Thanks in advance for any help you can provide!
Abbreviated Java Console output:
Java Plug-in 1.6.0_26
Using JRE version 1.6.0_26-b03-384-10M3425 Java HotSpot(TM) 64-Bit Server VM
load: class ZeroApplet.class not found.
java.lang.ClassNotFoundException: ZeroApplet.class
    at sun.applet.AppletClassLoader.findClass(AppletClassLoader.java:211)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    at sun.applet.AppletClassLoader.loadClass(AppletClassLoader.java:144)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
    at sun.applet.AppletClassLoader.loadCode(AppletClassLoader.java:662)
    at sun.applet.AppletPanel.createApplet(AppletPanel.java:807)
    at sun.plugin.AppletViewer.createApplet(AppletViewer.java:2389)
    at sun.applet.AppletPanel.runLoader(AppletPanel.java:714)
    at sun.applet.AppletPanel.run(AppletPanel.java:368)
    at java.lang.Thread.run(Thread.java:680)
load: class JavaToJS.class not found.
java.lang.ClassNotFoundException: JavaToJS.class
    at sun.applet.AppletClassLoader.findClass(AppletClassLoader.java:211)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    at sun.applet.AppletClassLoader.loadClass(AppletClassLoader.java:144)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
    at sun.applet.AppletClassLoader.loadCode(AppletClassLoader.java:662)
    at sun.applet.AppletPanel.createApplet(AppletPanel.java:807)
    at sun.plugin.AppletViewer.createApplet(AppletViewer.java:2389)
    at sun.applet.AppletPanel.runLoader(AppletPanel.java:714)
    at sun.applet.AppletPanel.run(AppletPanel.java:368)
    at java.lang.Thread.run(Thread.java:680)

I just went up to check the LiveConnect object functionality page AND IT WORKED THIS TIME! I must confess, this is very mysterious. I will do some more checking and reply here if I can determine why it is working now (and more importantly, why it didn't work before).

JRE Versions...

Hi all,
I am newly employed at a different company and used to use Java to write little widgets and apps at my last job. I have started doing so again at my new job and people are pleased... for the most part. A big problem that has occured is the company I now work for has a tool that was writen in an old JRE, JRE v1.4.2_16, and according to our SW department it will not run in JRE 5 or 6. This is unfortunate as I do my developments with the latest JRE, and have already written a handful of tools for my team. Our SW folks tell us that we must uninstall JRE 5 or 6 and install the older version in order for the program to run.
This is now affecting me and everyone on my team very negatively. I've put in requests that the company update its SW so that it runs in the latest JRE, but to no avail. As my tools and widgets have become widespread (but everyone on my team HAS to use the copmany SW that only runs in JRE v1.4.2_16) my boss has decided that we all should uninstall my programs and the latest JRE. To try and continue to utilize my SW, my boss is going to buy me another PC which will have all of my tools on it that people can access via the network. While this seems like an ok solution, I was wondering if anyone had any other solutions. Is there a way to write some code somewhere or setup Java in the control panel so that when this particular program tries to run that it uses JRE 1.4.2_16? Note that the program is launched from a web browser.
Thanks for the input!

newbie_josh_ee wrote:
I am not sure exactly why the program won't run in Java 6. I have not been told.The real question here isn't why they say it, but if you explicitly run it in Java 6, will it actually work if you force it to.
I've got a similar problem here where we have these applets, and some people in another group have other applets they must use for things, and the people who supplied those 3rd party applets did the stupid thing of using the object/embed tags set so they can't run except in an explicit version.
This causes problems if running ours and it uses a newer JRE on the system, the 3rd party ones will not run due to Java plug-in collisions. I did some testing, and there is nothing specifically wrong with using their applets with newer Java versions, except that their web pages say no. But I can't deploy a modified version of the page.
My guess is the "logic" is that it works fine in version X, so if I restrict to version X only, I don't have to deal with complaints if there's a bug in Java version Y that breaks the app (which does happen sometimes). The problem with that is Java updates so frequently and a large user base is going to have any number of different versions of Java that if you force them into one specific version, you are going to cause conflicts with other tools, and that causes bad user experiences.
I've also seen sites that say (not so much anymore) that they can't run in IE7. Quick registry edit to make it look like IE6 and things work perfectly fine.
It's not likely the code will not actually work. Just bad html or run script. Unless the code actually does a version check, and then that's another issue. But still shouldn't be necessary for them to have done.

Java is blocked. Don't know why. Error: Application Blocked Java Plug-In 10.51.2.13 using JRE version 1.7.0_51-b13 Java HotSpot(TM) Client VM

I keep receiving this message when trying to use http://www.exodus-chats.org/DolTerias . it uses a java based chat system, and won't allow me to open the application. I've tried checking through my options menus, but I've found no reason as to why this can be blocked. The only thing I've come up with is my plug ins, but it doesn't allow me to change anything to allow the app to be used.
Application Blocked
Details: Java Plug-In 10.51.2.13 using JRE version 1.7.0_51-b13 Java HotSpot(TM) Client VM

Starting in Java 7 Update 51, sites that would normally be blocked based on your Java Security settings can be added to an Exceptions list, via the Java Control Panel. See the Java Help page [http://www.java.com/en/download/faq/exception_sitelist.xml How can I configure the Exception Site List?] for details.
Ref: http://kb.mozillazine.org/Java#Java_security_prompts

Problem selecting the right jre version with jnlp

I am using Webstart 1.4.2.
When instaling, it correctly found 2 jre versions on my system, 1.4.1_03 and 1.4.2.
Because our application currently is not working with 1.4.2 I need to force webstart to use 1.4.1_03.
I tried to set the tag <j2se version="1.4.1_03"
When loading from the websever I get a "Error Code 11 (11 Could not locate requested version) "...same if I explicitly set to 1.4.2.
I suspect that webstart is checking the "platform version" which are set for both to 1.4 and not the "product version" (see java preferences in webstart).
Does somebody know if there is another jnlp tag I can use to force a specific version? or any other workaround.
In my opinion this is a bug webstart should check the product version
Thanks Marc

had the same problem...
ad the url and try again:
<resources>
<j2se version="1.4.1_03" href="http://java.sun.com/products/autodl/j2se"/>
<jar href="...
as far as I now are not all JRE's available for autodownload.
Good luck!

Use different JRE versions in Oracle Discoverer 10g(10.1.2.0)

Hello.
We have a Oracle Forms application which also uses Discoverer Plus and Reports.
Problem is we have some user clients who uses XP/IE 6.0 while otheres has Vista IE 8.0.
Based on here
http://www.oracle.com/technetwork/middleware/ias/downloads/as-certification-r2-101202-095871.html#BABGCBHA
depending on OS/browser different plugin versions are required. If we
Can we have different JRE versions in separate clients? Kinda confused with the matrix.

Hi;
Please check below which could be helpful for your issue:
Overview of Using Java with Oracle E-Business Suite Release 12 [ID 418664.1]
Deploying Sun JRE (Native Plug-in) for Windows Clients in Oracle E-Business Suite Release 12 [ID 393931.1]
Oracle Jinitiator and Sun JRE/JPI Support for Oracle Forms Applications [ID 555720.1]
Regard
Helios

JRE version problem (XML Parsing)

Hi,
I posted a question earlier about an issue I'm having with an applet running in the Eclipse IDE but not in-browser. I have checked the JRE version for both and the browser is running 1.6.0_01 and the IDE is running 1.5.0_06. Now I could uninstall the former to force the browser to load the latter I believe but that doesn't solve the issue as I would need it to run on the newer JRE version.
So my question is, what would cause the following error to occur in a later version of the JRE?
Exception in thread "Thread-9" javax.xml.parsers.FactoryConfigurationError: Provider org.apache.xerces.jaxp.DocumentBuilderFactoryImpl not found
Thanks in advance,
Dan

It has nothing to do with new or old version of jre it has to do that the explorer jre (5) can not find the jar file it needs. It is looking for the class org.apache.xerces.jaxp.DocumentBuilderFactoryImpl but it can not find it.
In you Eclipse you do have this jar that's why it is running, just copy the jar to the lib or lib/ext folder in the jre 5 and everything should work.

JVM Loader Error: Unable to find supported JDK or JRE version

Hello,
I am trying to use Visibroker (Borland version 6.5) with JDK 1.5.2
When I try to run idl2java, it gives me the following message:
JVM Loader Error:
Unable to find a supported JDK or JRE version. The JVM Version should be either 1.3.1 or 1.4.1 and above.
Check your installation and use -VBJjavavm or -javahome(vbj only) to specify the JDK or JRE location
I am using eclipse IDE - i created an external tool configuration for idl2java giving the argument *.idl
I looked in the forum and tried the suggestions given in this thread
http://forum.java.sun.com/thread.jspa?threadID=376403&messageID=3052413
Where am I going wrong. Can someone help me?
Thaks
Manju

Hi,
I don't know if you got an answer to this problem. It looks like you need to install Borland Service Pack 1 (for BES 6.5) to fix this issue. I spent a couple of days squirming, trying to figure out this issue.
Hope this helps.
Regards,
Sony.

AIX JRE version vs Sun JRE version

hi,
we have a 3th party application installed on an AIX server. The minimum JRE-version for the application is 1.4.2_09. If you type java -version on AIX you get:
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2)
Classic VM (build 1.4.2, J2RE 1.4.2 IBM AIX build ca1420-20040626 (JIT enabled: jitc))
I was wondering if the IBM version-numbers are the same as SUN's or is it possbile that IBM 1.4.2 is 'the same' as SUN 1.4.2._10 or such?
many thanks!
Stijn

Hi George,
Apologies, these release notes were referring to some Security vulnerabilities with some specific JRE versions.
You can check the currently runing JRE version using:
This cannot be verified from UI, but you can verify from command-line (see command and output below).
C:\Program Files\Cisco Systems\Cisco IP Communicator\JRE\bin\java.exe" -version
java version "1.4.2_19"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_19-b04)
Java HotSpot(TM) Client VM (build 1.4.2_19-b04, mixed mode)
Not sure about the second part of this query, will let others to comment on that.
Thanks,
Anand

JVM version check -version:1.4* does not always work

Jdk1.5 (and later 1.4.2) has a version checking feature in java -version: flag.
i.e.,
[ronnc@bill ronnc]$ java -version:1.4.2_05-b04 -version
java version "1.4.2_05"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_05-b04)
Java HotSpot(TM) Client VM (build 1.4.2_05-b04, mixed mode)
[ronnc@bill ronnc]$ java -version:1.4* -version
java version "1.4.2_05"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_05-b04)
Java HotSpot(TM) Client VM (build 1.4.2_05-b04, mixed mode)
I have this working on some machine but on several machine it just refuses to work in a very perculia way.
[builder@apollo builder]$ java -version:1.4.2_05-b04 -version
java version "1.4.2_05"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_05-b04)
Java HotSpot(TM) Client VM (build 1.4.2_05-b04, mixed mode)
[builder@apollo builder]$ java -version:1.4* -version
Unable to locate JRE meeting specification "1.4*"
I've looked into the launcher source code (it checks version info from dir name or jre/RELEASE file) and I think i've setup everything right still having trouble understanding why it doesn't work on some machine. It seems to me that acceptable_release() function doesn't return correctly.
Anyone have any idea why? Also does anyone know how I can get the source to libjvm.so so that I can look at what it's doing.
rOnn c.

It's not documented anywhere except from the command line help
[ronnc@bill ronnc]$ java -showversion
java version "1.4.2_05"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_05-b04)
Java HotSpot(TM) Client VM (build 1.4.2_05-b04, mixed mode)
Usage: java [-options] class [args...]
(to execute a class)
or java [-options] -jar jarfile [args...]
(to execute a jar file)
where options include:
-client to select the "client" VM
-server to select the "server" VM
-hotspot is a synonym for the "client" VM [deprecated]
The default VM is client.
-cp <class search path of directories and zip/jar files>
-classpath <class search path of directories and zip/jar files>
A : separated list of directories, JAR archives,
and ZIP archives to search for class files.
-D<name>=<value>
set a system property
-verbose[:class|gc|jni]
enable verbose output
-version print product version and exit
-version:<value>
require the specified version to run
-showversion print product version and continue
-jre-restrict-search | -jre-no-restrict-search
include/exclude user private JREs in the version search
-? -help print this help message
-X print help on non-standard options
-ea[:<packagename>...|:<classname>]
-enableassertions[:<packagename>...|:<classname>]
enable assertions
-da[:<packagename>...|:<classname>]
-disableassertions[:<packagename>...|:<classname>]
disable assertions
-esa | -enablesystemassertions
enable system assertions
-dsa | -disablesystemassertions
disable system assertions
Do you see -version:<value> ? I've done my research please do yours.

IE not paying attention to version checking in JWS

I have an application which requires Java 1.6.0_10 or later, and I have the following JNLP:
<?xml version="1.0" encoding="UTF-8"?>
<jnlp spec="1.0+"
     codebase="http://pebbleit.hope.edu/game"
     href="HCG-Applet.jnlp">
    <information>
        <title>Pebble It</title>
        <vendor>HCG Group/Hope College</vendor>
    </information>
    <resources>
        
        <j2se version="1.6.0_10+"
              href="http://java.sun.com/products/autodl/j2se" />
        <jar href="hcg.jar" main="true" />
        <jar href="miglayout-swing.jar" main="false"/>
          <property name="jnlp.packEnabled" value="true"/>
    </resources>
     <applet-desc main-class="cusack.hcg.gui.TheApplet"
     name="Pebble It"
     width = "800"
     height = "600">
     </applet-desc>
</jnlp>And the following code to launch it:
<script src="http://www.java.com/js/deployJava.js"></script>
<script>
// using JavaScript to get location of JNLP file relative to HTML page
var dir = location.href.substring(0, location.href.lastIndexOf('/')+1);
deployJava.launchButtonPNG='http://pebbleit.hope.edu/images/Pebble_Button.gif';
var url = dir + "game/HCG-Applet.jnlp";
deployJava.createWebStartLaunchButton(url, '1.6.0_10+');
</script>In Firefox, the version checking works and it updates Java as needed.
In IE 8 (perhaps all IE), it does NOT check this, but tries to run it anyway. I was not totally suprised (but still irritated) when it did this with Java 1.6.0_7 installed since the documentation mentions that some browsers do not check the minor revision, but when I just tried it with Java 5.0 update 19, I was kind of shocked. It downloads the jarfile and tries but fails to run it (of course it fails!).
So, is there something wrong with my files?
Thanks.
EDIT: Well, I just tried with Firefox on a machine and it did the same thing. Strange. I KNOW in the past it did it correctly with Firefox. So now I suspect I introduced an error somewhere--Anything obvious in my files?
Edited by: WhyNotFerzle on Mar 27, 2010 1:04 PM
Another EDIT: I am starting to suspect that something is getting cached in some unknown location. I have done several tests using the machine in question, and I know it USED to update properly on that machine. This morning I deleted all new version of Java until I only had Java 5.0 update 19, and it now fails on both IE and Firefox--running JWS 5.0 and failing to load (obviously because the code is Java 6). So I am wondering if since it ran once, it is no longer doing the check properly, somehow storing information somewhere that it has the proper Java. Is this possible? I have tried clearing the JWS cache, and that didn't seem to help. I am baffled.
Edited by: WhyNotFerzle on Mar 27, 2010 1:08 PM

greencosmos wrote:
Hi, for the exact version check and update of JRE I actually do not know much.
Here's link for version checking and auto update.
http://java.sun.com/javase/6/docs/technotes/guides/javaws/developersguide/launch.html#creating
Hope this could be some help.The top of that page indicates that the information on it is out of date.
In any case, I have read and reread the documentation I can find about JWS, and it is inconsistent. Some pages claim that if the Java version does not meet the minimum requirement, it will redirect to the download page. Other pages claim it will automatically download it. As I have outlined above, it seems to do one or the other on different machines for no discernible reason.
I even looked at the source code for createWebStartLaunchButton:
     * Outputs a launch button for the specified JNLP URL. When clicked, the
     * button will ensure that an appropriate JRE is installed and then launch
     * the JNLP application. minimumVersion is of the form #[.#[.#[_#]]], and
     * is the minimum JRE version necessary to run this JNLP application.
     * minimumVersion is optional, and if it is not specified, '1.4.2'
     * will be used.
     * If an appropriate JRE or Web Start installation is detected,
     * the JNLP application will be launched, otherwise installLatestJRE()
     * will be called.
     * After installLatestJRE() is called, the script will attempt to detect
     * that the JRE installation has completed and launch the JNLP application,
     * but there are circumstances (such as when the JRE installation
     * requires a browser restart) when this cannot be fulfilled.
    createWebStartLaunchButton: function(jnlp, minimumVersion) {
        if (deployJava.returnPage == null) {
            // if there is an install, come back and run the jnlp file
            deployJava.returnPage = jnlp;
        var url = 'javascript:' +
                  'if (!deployJava.isWebStartInstalled("' +
                      minimumVersion + '")) {' +
                      'if (deployJava.installLatestJRE()) {' +
                        'if (deployJava.launch("' + jnlp + '")) {}' +
                      '}' +
                  '} else {' +
                      'if (deployJava.launch("' + jnlp + '")) {}' +
        document.write('<' + 'a href="' + url +
                       '" onMouseOver="window.status=\'\'; ' +
                       'return true;"><' + 'img ' +
                       'src="' + deployJava.launchButtonPNG + '" ' +
                       'border="0" /><' + '/' + 'a' + '>');
    },It clearly says in the documentation and can be seen in the code that it is supposed to automatically install the latest JRE.
So, why isn't it doing this consistently?
A further look at the file may help--the documentation for installLatestJRE:
     * Triggers a JRE installation. The exact effect of triggering an
     * installation varies based on platform, browser, and if the
     * Deployment Toolkit plugin is installed.
     * In the simplest case, the browser window will be redirected to the
     * java.com JRE installation page, and (if possible) a redirect back to
     * the current URL upon successful installation. The return redirect is
     * not always possible, as the JRE installation may require the browser to
     * be restarted.
     * In the best case (when the Deployment Toolkit plugin is present), this
     * function will immediately cause a progress dialog to be displayed
     * as the JRE is downloaded and installed.
     */So apparently if the Deployment Toolkit plugin is not present, it redirects. What is the Deployment Toolkit plugin? The script that calls the function is called the Deployment Toolkit script. Are these different things?
Seriously, why is this so difficult? All I want is for the JRE to update when needed if a user clicks the launch button. I do not know who thought just automatically redirecting to the download page was a good idea as a fallback, but it is very confusing to people. ("Java? What's Java? I don't want to download Java. I clicked on a button to play Pebble It. This must be a virus or something. I guess I'll go do something else."). At least it could pop up a window saying "You need a newer version of Java in order to run this. Do you want to download it now?"
In any case, doesn't ANYBODY know how to make this work properly? What should boil down to 1 line of code is taking me HOURS to figure out!
By the way, I'd add Duke Dollars, but the option isn't showing up. I must not have anymore.

Get default JRE version...

If several versions of Java were installed in a client machine,
and in IE -> Internet Options -> Advanced Tab only one is enabled / checked.
How to get the default / checked JRE version in JSP ?

They are called Java SERVER Pages for a reason. They run on the server, not the client. The client machine is completely irrelevant to JSP/Servlets, so what version of java you have installed their doesn't matter at all.
Unless of course you want to run an applet. Whereas you put the appropriate constraints into your applet/object tag.
Check out this page: http://java.sun.com/products/plugin/1.3/docs/tags.html

How to find out jre version installed ,using a java program?

Hello,
Is there any way to find out the installed JRE version using a java program ?
The requirement is as follows:
There is a html page with 4 steps to install a software. each step is a link, which upon clicking does its work.
the first step is to install jre 1.4.2_11 if its not installed in the system. But how can i find out whether jre 1.4.2_11 is installed or not ?
Thanks in advance

For the hell of it... here is a list of properties you can query:
java.version Java Runtime Environment version
java.vendor Java Runtime Environment vendor
java.vendor.url Java vendor URL
java.home Java installation directory
java.vm.specification.version Java Virtual Machine specification version
java.vm.specification.vendor Java Virtual Machine specification vendor
java.vm.specification.name Java Virtual Machine specification name
java.vm.version Java Virtual Machine implementation version
java.vm.vendor Java Virtual Machine implementation vendor
java.vm.name Java Virtual Machine implementation name
java.specification.version Java Runtime Environment specification version
java.specification.vendor Java Runtime Environment specification vendor
java.specification.name Java Runtime Environment specification name
java.class.version Java class format version number
java.class.path Java class path
java.library.path List of paths to search when loading libraries
java.io.tmpdir Default temp file path
java.compiler Name of JIT compiler to use
java.ext.dirs Path of extension directory or directories
os.name Operating system name
os.arch Operating system architecture
os.version Operating system version
file.separator File separator ("/" on UNIX)
path.separator Path separator (":" on UNIX)
line.separator Line separator ("\n" on UNIX)
user.name User's account name
user.home User's home directory
user.dir User's current working directory

JRE version check?

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