RE: Re: RPGIV: RPG and Java

Thanks, Bill. I'll keep your tips in mind. 

I was wondering...some of my Javabeans simply read DB2 files and write a
text file (e.g., xml, csv, fixed-width format) to a PC folder.  I could code
a Java program that instantiates and calls the Javabean methods, then simply
have an RPG program call the Java program. Would I get better performance by
calling a Java program from an RPG program rather than having the RPG
program use the Javabean methods directly via prototyping?

Thanks,
Kelly

-----Original Message-----
From: William Fly [mailto:billfly@xxxxxxxxxxxxxx]
Sent: Monday, January 12, 2004 9:43 AM
To: kcookson@xxxxxxxxxxxx
Subject: Fw: Re: RPGIV: RPG and Java


Kelly,
     I have written an RPG ILE portal program to a Java XML translator.  I
learned quite a bit getting it to work.  First of all, the initial call from
the RPG to the Java is pretty slow, because the Java Virtual Machine is
beining loaded into that job.  After the JVM is initialized, everything
moves swiftly.  Also, it take extra calls into Java to pass and return Java
Strings.  I would highly recommend passing in RPG character (varying) fields
which Java can handle as byte arrays.  Also, returning a byte array will
return an RPG character field with the varying keyword.  That way you do not
create extra Java String objects that are difficult to get rid of and can
cause a tremendous amount of garbage collection and you Java program to slow
down over time.  Using the byte arrays seems to keep the execution of the
Java program very consistent over time.  Assuming your Java program is not a
static method, you will need to call the Java program's constructor which
returns a Java 
 object.  That Java object must be return on every method call as the first
parameter, but do not define that parameter in the prototype.  Example:
      d xml             s               o   class(*java : SboXmlXlator)
 
      d constructor     pr              o   extproc(*java : SboXmlXlator :
      d                                             *constructor)
 
      d xml2Fixed       pr         32767a   varying
      d                                     extproc(*java : SboXmlXlator :
      d                                             'xml2Fixed')
      d                            32767a   varying const
      d                            32767a   varying const
      d                            32767a   varying const
 
        xml = constructor();
        response =  xml2Fixed(xml : object : tag : request);  // notice 1st
parameter is
                                                          // object returned
from
                                                          // constructor,
not in prototype.
 
Also, you must set your classpath with an ADDENVVAR command before doing
anything.  The Java object must be in the an IFS directory and that
directory must be on the classpath.  That should save you some of the scars
that I have accumulated getting this to work.
Bill
(copy of post to RPGIV@xxxxxxxxxxxxxxx)

> I have coded a few servlets that use Toolbox for Java to process iSeries
DB2
> files. I would now like to turn these servlets into beans and run them on
> the iSeries. However, since Java is not a standard language in our shop, I
> need to make the beans available through RPG programs.
> 
> One strategy would be to make RPG programs that call (and pass parms to)
the
> Java programs. The Java programs would then instantiate and use the beans.
> Another strategy would be to use Java-RPG interoperability and have the
RPG
> programs use the beans' methods directly. 
> 
> I'd appreciate any insights into why and under what circumstances one
> strategy would be preferable to the other.  I'd also like to hear about
any
> pitfalls of Java-RPG interoperability, and whether people think Java-RPG
has
> a bright or gloomy future.
> 
> Thanks,
> Kelly
> 
> -- 
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