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This thread about RPG and Java got me started.
I wrote a quickie helloWorld that takes but one parm - the name. Compiled,
ran in QSH and it works. After doing some reading, I prototyped it in RPG
and commenced my struggle with the CLASSPATH. Hint: after changing
CLASSPATH via ADDENVVAR, sign off and on. It appears that the JVM reads the
class path when it is first started. To get a new class path, you need a
new JVM and thus, a new job. Anyway, I finally got the thing to run. I
think. It flashes something very quickly and then it's gone.
Barbara's mention about DeleteLocalRef lead me to The Manual, in this case,
the RPG Programmers Guide. There's a bunch of cool things there, and among
them is 'Calling Java Methods from RPG', item 4:
"Normally, Java does its own garbage collection, detecting when an object is
no
longer needed. When you create objects by calling Java constructors from
your
non-native RPG procedure, Java has no way of knowing that the object can be
destroyed, so it never destroys them. If you know you are not going to need
an
object any more, you should tell this to Java by calling the JNI function
described in "Telling Java you are finished with a temporary object" on
page 174."
I don't want stuff floating about: I want to use freeLocalRef to clean up my
Java string in the RPG program. It appears I need to obtain the JNI
environment pointer first. So off to page 176 I go and my real odyssey
begins. I copy/paste the getJniEnv procedure into Code/400 and it's
hideously misaligned and uses a goofy character for the apostrophe. Fix
that and compile. No prototypes. I read a bit more and sure enough,
QSYSINC/QRPGLESRC member JNI has a PILE of prototypes. Add that and
compile. Binding fails. Turns out there's a Java service program QJVAJNI
that has all the stuff I need. That guy is in binding directory QUSAPIBD.
(Neither of these things is mentioned in the book.) Add that and compile.
"Definition not found for symbol '_QRNX_JNI_FREE_OBJ'."
Well, this isn't in my RPG source and it isn't in the /copy JNI member.
It's not in the cross reference the compiler prints either, so I'm guessing
it's some internal thing. Other '_QRNX' references appear in QRNXUTIL,
QRNXIE and QRNXIO.
Searches in the APAR and PTF database on '_QRNX_JNI_FREE_OBJ' and 'RPG Java'
reveal nothing. What am I doing wrong?
h thread(*serialize) bnddir('QUSAPIBD')
* dbgview(*list) tgtrls(V5R2M0)
d helloWorld pr extproc(*java:
d 'helloWorld':
d 'main')
d static
d args o class(*java: 'java.lang.String')
d const
d dim(256)
d options(*varsize)
d newJavaString pr o extproc(*java:
d 'java.lang.String':
d *constructor)
d inpValue 256a const varying
d getJniEnv pr *
* the IBM JNI library
/copy qsysinc/qrpglesrc,JNI
d string s like(newJavaString)
c eval string = newJavaString('Buck')
c callp helloWorld(string)
c eval *inlr = *on
* getJniEnv
p getJniEnv b export
d getJniEnv pi *
d rc s like(jint)
d rpgRc s N
d jvm s * dim(1)
d env s *
d bufLen s like(jsize) inz(%elem(jvm))
d nVMs s like(jsize)
d initArgs ds likeds(JDK1_1InitArgs)
d attachArgs ds likeds(JDK1_1AttachArgs)
/free
//----------------------------------------------------------------
// See if there s a JVM started
//----------------------------------------------------------------
rc = JNI_GetCreatedJavaVMs (jvm : bufLen : nVMs);
//----------------------------------------------------------------
// If JVM is started, just attach to it, to get the env pointer
//----------------------------------------------------------------
if (rc = 0
and nVMs > 0);
attachArgs = *ALLX'00';
JavaVM_P = jvm(1);
rc = AttachCurrentThread (jvm(1):
env : %addr(attachArgs));
//----------------------------------------------------------------
// If JVM is not started, start it with the default classpath.
//----------------------------------------------------------------
else;
initArgs = *ALLX'00';
rc = JNI_GetDefaultJavaVMInitArgs (%addr(initArgs));
if (rc = 0);
rc = JNI_CreateJavaVM (jvm(1) : env : %addr(initArgs));
endif;
endif;
if (rc = 0);
return env;
else;
return *NULL;
endif;
/end-free
p getJniEnv e
// Hello, world!
// to use: java helloWorld <yourname>
import java.io.*;
public class helloWorld
{
public static void main(String argv[])
{
System.out.println("Hello, " + argv[0]);
return;
}
}
--buck
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