Running Multiple Java Versions

Question

Hopefully someone can help me because I am apparently brain dead. I have searched and read through a lot of this forum as well as others for help in resolving my problem and I am just not getting it.

I have 2 Java WebApps that I need to run for Johnson Control HVAC units. The one unit is old and strictly requires Java 1.6.0_21. There are no upgrade options available for this unit. Just hundreds of thousands of dollars to replace the whole system. But the system works just fine so I am not interested in replacing it.

Now I have another unit which my company just took over at another location that uses a similar control unit but runs on Java 1.7.0_49 or 69 I can't remember. I have both versions installed on my computer but only the newer unit with Java 1.7 works. My older one now comes up with Unable to Launch Application Error. I have tried all these things and either I am just plain doing it wrong or something else that I am not catching is up.

I tried going into the Java Control Panel and unchecking Enable 1.7. That had no affect, even after rebooting.

I went into the Environmental Variables and under Path I have no Path to Java. So I added the path to the Java 1.6 version which also had no affect.

I have a batch file on my desktop to run the older app because it's web URL is a mile long. In this batch file I tried to add set JAVA_HOME variable and a set PATH variable for Java 1.6 which also had no affect.

I tried just doing java -version:1.6 from the cmd prompt which also did not allow the program to start.

I got it so when I did java -version from the cmd prompt it would tell me 1.6.0_21 for the version but I still can't get the program to load.

So I uninstalled 1.7 from the computer and tried it again. Still would not load the program. I had to reinstall the 1.6 before the older program worked. But once I reinstalled 1.7 I was back in the same boat.

I tried re-installing both programs using the STATIC=1 command through cmd prompt and still only version 1.7 runs and the older 1.6 does not.

I do get a message when I try to load the 1.6 that says, the program has requested an older outdated version of the program. Open with new version recommended or open in the older requested version 1.6.0_21. I select open in the older version but still get the Can Not Launch Application Error.

I have also tried going into the advanced settings and unchecking Internet Explorer for the Browser in the 1.7 control panel and going into the 1.6 control panel and checking Internet Explorer.

What am I doing wrong here or what am I missing? Any help would be appreciated.

This is a Windows XP 32 bit computer. Nothing special, just a word processor mostly.

Answer 1

You are swimming upstream, but it isn't a very large or strong stream, and this can be done.

The upstream part is that most instructions for doing this assume you are going to run only one version of the JVM on a given machine.

The good news is that Java doesn't require this, and is not set up so that it is difficult to run two at the same time. You just have to be rigorous about where each of them get their information.

I would recommend not "installing" EITHER of them. Do not put the executables' or the libraries' directories on your path variable, and do not define a CLASSPATH variable on the machine globally. You will need to unpack a runtime environment for each JVM, each in their own directory tree.

Make one batch file to run each version. It will define its own path variable, and its own classpath (either with SET CLASSPATH= or using the classpath JVM argument).

Good luck.