I'm going to propose to a client that I build some batch jobs in Java that will run on their mainframe and/or AS/400s (sorry System z and System i). Both platforms are up to date system software wise. I'm wondering if anyone has done this and can provide any pointer or gotchas to watch out for.
The motivation is to have access to the tools and libraries available to java for doing things like calling web services and creating PDFs.
Java is well supported on both machines.
On z/OS the whole Webshere application server suite and associated process servers and ESBs have been ported.
The main motivation is to get direct access to legacy DB2 (and to a lesser extent IMS) databases from a "modern" application.
I have also seen Java for CICS but it was very problematic (JVM was constantly re-initialised).
I have written some JNI code to expose a native assembler application API over websphere.
I am not sure of the situation on the iSeries, but most iSeries shops I know are still clinging to RPG IV.
The main gotchas are are UTF-16 to/from EBCDIC conversions. They take time and you really need to be careful about LOCALE settings (its easiest if your USS shells, DB2 database are set to identical code pages).