You really don't want those in Java400/ext. That's where java extensions go. Java extensions are not subject to the same kind of security checks as normal jars and it is really hard to override jars in that path. For the most part, only security extensions to java should go in the ext path.
Create a directory in the IFS and put all your POI jars in there. When you start your RPG program, make sure the classpath includes a full path to*EACH* jar.
FWIW, depending on what operating system you're using, java will reside in either /QIBM/ProdData/Java400 or /QOpenSys/QIBM/ProdData/Java. All the J9 JVM's live only in QOpenSys.
As an Amazon Associate we earn from qualifying purchases.
Operating expenses for this site are earned using the Amazon Associate program and Google Adsense.