I have existing RPG4 programs with green screens, i would like to be able to call the rpg programs with Java and bypass the green screens.
I have done some research on this and IBM OAR (Open Access: RPG) keeps coming up. but i have not found a working example yet.
My goal is to create a web app to collect the the same information and feed it to the back end RPG
any help would be greatly appreciated
On
OAR is probably going to be your best bet....
However, every example I can think of that I've seen has resolved around building a handler to replace a printer file (PRTF) or physical file (PF).
Replacing a display file (DSPF) is a whole other ball game. Primarily because the 5250 protocol is an "intelligent" protocol; unlike dumb character type protocols such as used by ANSI/VT100.
It certainly can and had been done. If you have a single basic screen, you might be able to do it. But for a complex application with multiple screens and subfiles you'll probably have a tough time. Especially if you don't have a in depth understanding of the 5250 protocol.
I'd recommend you take a look at one of the vendor toolset designed to use OAR to replace a 5250 screen with a web page. Those vendors have put years of time and effort into developing the handler needed.
http://www.profoundlogic.com/solutions/rpg-application-modernization.html
https://asna.com/us/products/wings
You might find the following publication useful:
Modernizing IBM i Applications
Lastly note that ROA isn't the only option. There's an older technique, "screen scraping" in which your application basically emulates a 5250 terminal. It's simpler than a full ROA handler, but the end result is simpler also. IBM has it's own tool, HATS. And for instance Profound logic also has a tool, GENIE. But you could conceivably build your own screen scraper, the opensource TN5250J would probably be a place to start. But even this would be non-trivial.
On
You should use a mix of parsin json on the iseries(this eliminates the subfile problems), one good javascript framework( I've used Extjs) and The Apache server for I.
I've developed a HTTP services framework based on json parameters send directly from the browser using Ajax, processing each request with any ILE language program(mostly rpgle) and returning the result in pure json created inside the program. With this approach, you just send/receive business data, leaving the front-end to the Javascript framework.
Hope this helps. Contact me if you need more help.
EDIT
Delete: You can't.
Insert: A beginner will need to master several complex new concepts before tackling this.
END-EDIT
At least, not without changing the RPG program. Web requests are processed by server jobs, which run in batch - they are not connected to a 5250 terminal. Because they aren't connected to a terminal, when the RPG program tries to open the display file, it will fall over because there's no terminal to attach to.
In order for this to work you'd have to alter the RPG program to not try display file I/O if called by a batch process like a Java app (although Java isn't necessary in this web scenario).
One way to change the RPG program is to use input parameters; if you have them, then don't try to open the display file, but stuff the input parameters into the fields where the display file would have done. Since a display file also outputs from the program you'd need to reserve some parameters for the output information as well. This could get very ugly if a subfile is involved, as there would be potentially thousands of parameters.
OAR comes into the picture because one can write an OAR handler that continues to use the same display file I/O operations, but to direct the actual I/O elsewhere, like STDIN and STDOUT for an HTTP type application. Jon Paris and Susan Gantner have written an article called Getting a Handle on RPG's Open Access which you might find helpful. It's in the July 2010 e-edition of IBM Systems Magazine.
Better perhaps is to extract the business logic in the RPG program, implement it as stored procedures which can be called by the web application via traditional ODBC / JDBC. One can write stored procedures in RPG, so that's not as hard as it might seem.