How to check JRE version prior to launch?

Question

What\'s the best way to determine if the version of the JRE installed on a machine is high enough for the application which the user wants to run? Is there a way of doing it

Answer 1

An application built for a higher-version JRE will not run on a lower-version JRE. So you wouldn't be able to just add code to your application to check the JRE version - if the JRE version was incompatible, your JRE-version-checking code would not run in the first place.

What you'd have to do is have some sort of launcher application that is built for a lower-version JRE (1.3?) that checks the version and then launches your app if necessary. This sounds kind of kludgy to me.

What about checking the version during installation? Are you installing the app in a way that allows you to check environment variables, or do any sort of scripting?

Answer 2

Hmm .. call me a boring guy, but what's wrong with using Launch4J or any other native launcher, for instance.

Use a native launcher to check the JVM version before actually running your code. Java only solutions (in my book) only make sense when you deal with developers; once you hit end-users, you'll realize that they dont care about Java or its technical details at all. If you would have written your application in GW-Basic they would not care less as long as your application works.

If Java 1.6 is not installed, lauchner4j will point the user to the download page for JDK 1.6. Thats probably more suitable for your problem than doing magic in Java.

Answer 3

You could do this using reflection and two compilers. Compile a main class with the oldest java version you want to be able to run at all with. It checks the version using System.getProperty("java.version"), or whatever, and then uses reflection to load your real main class if that check passes, possibly even loading the jar directly. The JRE shouldn't load any classes that weren't referenced by your outer main class at compile time.

Answer 4

You might consider Java Webstart. Even if the name implies something like applets, it's about standalone-applications. Webstart is a launcher, that checks a JNLP-file (a simple XML-file, where you configure the download-location of your app, the needed Java-version and some other metadata) and starts your app with the correct JRE. It even updates the application, if a newer version is available. The downside is, you have to write a JNLP-file. Here is an example:

<?xml version="1.0" encoding="utf-8"?>

<!--
###############################################################################
#
# @(#)draw.jnlp 1.6 02/09/11
#
# JNLP File for Draw Demo Application
#
###############################################################################
 -->


<jnlp spec="0.2 1.0"
      codebase="http://java.sun.com/javase/technologies/desktop/javawebstart/apps"
      href="draw.jnlp">
   <information> 
      <title>Draw 4 App</title> 
      <vendor>Sun Microsystems, Inc.</vendor>
      <homepage href="http://java.sun.com/javase/technologies/desktop/javawebstart/demos.html"/>
      <description>A minimalist drawing application along the lines of Illustrator</description>
      <description kind="short">Draw Demo Short Description</description>
      <icon href="images/draw.jpg"/>
      <offline-allowed/> 
   </information> 
   <resources>
      <j2se version="1.3+" href="http://java.sun.com/products/autodl/j2se"/>
      <j2se version="1.3+"/>
      <jar href="draw.jar" main="true" download="eager"/>
   </resources>
   <application-desc main-class="Draw"/>
</jnlp> 

A second possibility is to use a launcher-program. An example is the Apache Commons Launcher. You can also write some launcher app yourself, but that's usually not worth the effort.

Answer 5

You can require a Java version when running the Java command, e.g. java -version:1.6* com.me.MyClass. Not sure if this works on all releases of Java, but it works OK on 1.6 anyway.

Answer 6

Here is the code to get the JRE version installed in a system.

var list = deployJava.getJREs();
var result = "";
result = list[0];
for (var i=1; i<list.length; i++)
{
    result += ", " + list[i];
} 
document.write("jre version : "+result);