Question: Has anyone had good experiences of talking direct to RPG programs running on a V5R4 iSeries machine from Java? If so, what are the recommendations of the community, and what pitfalls should I try to avoid?

From the various pieces of literature and spike solutions I have attempted it looks as though we can use ProgramCallBeans (either through PCML or xPCML), talking to the DataQueues (for asynchronous comms), or even JNI.

I'm looking for something that's robust, performant, quick to develop, easy to maintain, and easy to test (aren't we all!?!).

Answer: 
I suggest using IBM's Java Toolbox for Java. Put the JT400.jar into your classpath (or JT400Ntv.jar if the Java is running on the iSeries). I've used both the ProgramCall class and the CommandCall classes.

The com.ibm.as400.access.CommandCall class is easy to use. It has a simple constructor that you pass a com.ibm.as400.access.AS400 class to. Then just use the run method like this:

```
CommandCall command = new CommandCall(as400);
command.run("CPYF FROMFILE(BLAH) TOFILE(BLAHBLAH) CRTFILE(*YES)");

```

Of course, you wouldn't use that particular CL command, but you get the idea. When using the CommandCall class, it's always a good idea to process any messages that came from the command. In the one program I use this for, I display the messages to the user in a textbox on their screen like this:

```
AS400Message[] messageList = command.getMessageList();
for (int i=0;i < messageList.length;i++) {
String sMessageText = messageList[i].getText();
    sMessage+=sMessageText + "\n";
}

```

The com.ibm.as400.access.ProgramCall class takes more work, but it allows you to access the returned parameters. I use this one more often because I'm usually calling existing RPG worker programs that return values. For this, define a com.ibm.as400.access.ProgramParameter array. When you pass parameters to a program from Java, remember to convert them to AS/400-friendly values using a class like com.ibm.as400.access.AS400Text. The details of the ProgramCall command are better researched using IBM's documentation: <http://publib.boulder.ibm.com/infocenter/iseries/v5r4/index.jsp?topic=/rzahh/page1.htm>
I've had some success with PCML documents. I decided to use PCML since encoding the commandcall into a string when passing parameters to an RPG program can get really ugly.

PCML allows you to somewhat transparently pass java data types to an rpg program as a parameter. The drawback is that the xml in the PCML doc becomes a static interface and must be updated if the program is ever updated. With the right build tools, it might be pretty straightforward to automate the update of the pcml xml, but right now I'm doing this manually.

I've used this approach when the rpg program needs to be called from java, and the logic flow is controlled by the java program.

In a case where the logic flow was controlled by an rpg program, I've used dataqueues for both synchronous and asynchronous calls to java. This required writing a significant amount of code to standardize on how to read and write to dataqueues in a coordinated manner from different programming languages