How to check JRE version prior to launch?
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 using java-only stuff? I'd like the solution to work on Windows/Linux/MacOSX - if the JRE version is too low a message should be displayed. Currently I'm getting an exception if i try to run it on Java 1.5 (the app is built for Java 1.6). If there's no universal solution, what's the best way to do it on Windows?
Answer
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.