IBM Java on Linux

Question

What would be the use case of installing IBM Java on a Linux machine? We tested our application on Linux using Oracle Java but one of ours customers installed it on a machine which only has IBM Java and the application gives errors for some missing classes and jars.

I'm assuming that the IBM java would probably have been installed because some IBM products mandate use of IBM java but this should not be a deterrent to install Oracle Java in addition to IBM java. Is my understanding correct?

Please share your thoughts.

• Elliott Frisch: Did you know that IBM supports Java on hardware that Sun does not support? For example, the iSeries.

Answer 1

I believe IBM doesn't ship its Java as an independent package -- so, yes, if IBM Java is present it's because an IBM product was installed that came with the IBM Java environment. (IBM supports Java on some platforms Sun doesn't; I believe the reverse is also true -- I don't think IBM bothers producing its own Java for Solaris, for obvious reasons.)

There's no problem having multiple Java's installed, each in its own directory. In some Linuxes, the alternatives mechanism can be used to select which Java is the default when you type java at the command line; in others, you would have to manually change the path or adjust symbolic links appropriately (the later is what alternatives does semi-automagically).

If you're working in Eclipse, its configuration menus will let you pick which installed copy of Java it will use to execute/debug applications, either on a workspace-default level or per launch.

(I have something like eight JREs/JDKs installed on my Red Hat machine -- a mix between Sun and IBM. Some are for my own use, for testing code for compatibility or trying to reproduce customer bug reports. Some were installed because a particular tool shipped with its own JRE rather than risk possible incompatabilities with another version; that's the only reason I still have a Java 1.5 JRE installed, for example. It's an annoyance, and it slightly belies Java's original promise of "write once, run everywhere", but it does work.)

Answer 2

There is nothing stopping you from having multiple installs of Java on a single linux system. However when running your application, you need to make sure that you are using the oracle version of java and not the IBM version.

which java

and

java --version

can help you find which version of java you are using.

Java is usually installed under /usr/lib/jvm or something similar to that. Checking there can help you find which java installs you have available.

Answer 3

You are correct that IBM java comes with IBM product installation - IBM does not ship their Java as standalone product. However, they provide provision to download their JRE for Linux from developerworks.

Ideally product running on Oracle JRE should run on IBM JRE and vice versa. However, to ensure that each product on the system runs on the JRE they are tested on, set java home properly for respective products. In case both the products use the same system-wide environment variable (which should not be the case anyway) - you may need to tweak your product settings so it does not break any IBM product running on the system.

As long as you properly isolate multiple JREs as used by different products through product/system property settings, there should not be any issue.