Where should the Toolbox jar files be installed on IBM i?

There have been many situations in the past where problems were caused because users had old versions of the Toolbox jar files installed in non-standard locations on their systems, but didn't realize it.
Here are some locations where "rogue copies" of Toolbox jars and classes have been found on customers' IBM i systems:

/QIBM/ProdData/Java400/
/QIBM/UserData/Java400/ext/
/QIBM/ProdData/OS400/Java400/ext/
/QIBM/ProdData/OS400/Java400/jdk/lib/ext/
/QOPT/WEBSPHERE/was/setup.jar

Putting jars in extensions directories is dangerous and a frequent cause of hard-to-diagnose problems, because classes are found there before they are found in the application's normal Java classpath.

Note that some users have expanded the Toolbox jars into separate class files. So when hunting for rogue Toolbox classes, also look for files with pathnames such as .../com/ibm/as400/access/<className>.class

If your Java application is invoked from with Qshell, you could specify the "java -verbose" option. The output will be "noisy" on the screen, but afterwards you can press F6 to print the scroller, and then search the spool file for Toolbox classes to see where they are being loaded from.

To keep things simple, we recommend that the Toolbox jar files only be installed in their official locations:

/QIBM/ProdData/OS400/jt400/lib/jt400.jar
/QIBM/ProdData/OS400/jt400/lib/jt400Native.jar