Re: FW: java to RPG problem -- JAVA400-L



If I am not mistaken, this sample shows how to attach to previously started
JVM in the same job (if JVM was already started for this job, it is
reasonable to reuse it).
I do not think you can attach to any JVM on system.

    Alexei Pytel
always speaking for myself




                      "Christopher J.
                      Jewell"                  To:       
<java400-l@midrange.com>
                      <jewellcj@jewellc        cc:
                      onsult.com>              Subject:  FW: java to RPG problem
                      Sent by:
                      java400-l-admin@m
                      idrange.com


                      12/11/2002 08:01
                      PM
                      Please respond to
                      java400-l







>>Naturally I disagree with James' comments about Java!

I meant to say that I disagree with James' comments about RPG also: I guess
I need hardly say that ILE/RPG is a terrific and elegant language, superb
for programmer productivity and well-suited to heavy duty database
transaction processing native on the iSeries. The integration features with
Java are extremely well done - the only issue with Java integration that I
can see is the necessity to serialize for thread-blocking at the level of
the module (as mentioned earlier).

When it comes to calling Java from RPG, however, I need to be reassured
that
it is possible for an ILE RPG procedure to call into a specific instance of
a JVM running in OS/400 - for example a WebSphere Application Server
Instance. The RPG Programmers manual has the following rather obscure code
for finding an existing running JVM:
 *
      * See if there's a JVM started
     C                   Eval              rc = JNI_GetCreatedJavaVMs(
     C                                          jvm : bufLen: nVMs)
      *
      * If JVM is started, just attach to it to get the env pointer.
     C                   If                rc = 0
     C                                      and nVMs > 0
     C                   Eval              attachArgs = *ALLX'00'
     C                   Eval              JavaVM_P = jvm(1)
     C                   Eval              rc = AttachCurrentThread (jvm(1)
:
     C                                       env : %addr(attachArgs))
      *
      * If JVM is not started, start it with the default class path.
     C                   Else
     C                   Eval              initArgs = *ALLX'00'
     C                   Eval              rc =
JNI_GetDefaultJavaVMInitArgs(
     C                                           %addr(initArgs))
     C                   If                rc = 0
     C                   Eval              rc = JNI_CreateJavaVM(jvm(1) :
env:
     C                                           %addr(initArgs) )
     C                   EndIf
     C                   EndIf

The question is: how can the program know which is the correct JVM to
attach
to? For example, there may be a requirement always to attach to a given WAS
JVM instance. I suppose an alternative would be to customize the WAS
instance, on start up, to call out to RPG in order to insure that the WAS
instance is known to RPG. Maybe I'm way off-base here - if so, can someone
let me know!


Chris Jewell



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