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How can i use Java to call an existing RPG screen program?

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

EDIT
Delete: You can't.
Insert: A beginner will need to master several complex new concepts before tackling this.
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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.

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.

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.

Convert HTML to PDF in JAVA without using any librarys

So my problem is that we are trying to take a chunk of HTML code and, using java, create a PDF file from it for a customer to view. We don't want to make the customer install any third party converters, or use any of the java libraries (like Itext). Is this possible? The easier the solution the better. Maintaining format is a plus but not necessary.

Use a 3rd party library then wrap it up inside your distribution process so that the customer never sees it.
For example use a proper installer to install your program, there are lots of easy-to-use programs to generate installers for you.

Our solution is only client side Javascript and then uses external server to receive that, format it and return it. See http//www.xportability. com/XEPOnline/FOTestSuite.html for early example. The client side will be made available through github soon. The server side is a commercial solution with options for you or us to host. Or you could build your own as it works with XSL FO.

server-side network printing java / grails [duplicate]

I am java / grails developer working on redesigning a software system.
One of the requirements is to have a sever-side application send data to various network printers to print text data.
I searched the web for info on java network printing, and came up short
I looked into Java Print Service API, java.awt.print, javax.print and did not find anything on connecting to network printers.
Is what I am trying to do possible or favorable. The lack of findings leads me to believe that sever-side software does not interact with network printers directly.
If it can be done, please point me to some resources.

Network printers are typically treated no differently from locally connected printers; they are set up in the OS first and this makes them available to the Java Print Service.
If you need to print directly to a POS printer, they usually have their own binary protocol that you can use over TCP/UDP. Epson has the ESC/POS system, for example.
Depending on the print server, you may be able to send PostScript straight to the printer via CUPS/LRP/LPD/IPP. See http://www.cups4j.org and http://lpdspooler.sourceforge.net.

printer driver implementation in java

I need to implement a custom printer driver which does the following in the backgroud:
Create a PDF document of the document to print
Send the created PDF document to a predefined email address OR
call a web service and transmit the document there
The pinterdriver should be available for windows and mac osx. My prefered implementation language is Java.
Is this possible with Java?
Are there frameworks available which reduce the coding effort to a minimum?

Are you sure "driver" is really the word you are looking for here? Usually when one says a print driver they actually mean something that translates document data into commands for a printer. I think you are really looking for something of a pre-processor.
In any case, if you want it to look like a printer to the OS, it will be almost impossible to do purely in Java. Your best bet would be to create drivers for each of the platforms that use JNI(or just invoke a JVM), do your processing, then forward it on to the printer.
Although I do not know if a similar approach will work on Windows, what you want to do is almost trivial to do on OS X. Apple already provides a cups-pdf service that converts any printable document into a pdf, all you have to do is take that output, forward it to where it needs to go, then forward it to a printer, no need to do anything in Java.
For an example of how to do this, check out the following project:
https://bitbucket.org/codepoet/cups-pdf-for-mac-os-x/downloads

Windows can be configured to send printer output to a file. You can create a printer in Windows that uses a PostScript driver, and writes it to c:\myfile.txt
In Windows: Add a Printer, Select Local printer, Select Create a new port, and type the file name (Full path) you want to use. Then pick the driver you want, which your Java program will have to parse. Generic text could be useful in some cases, or Postscript if you need all that formatting, and can handle parsing it.
Unlike the "File:" option under existing ports, it will not ask the user for a filename. It will just automatically save to the specified file every time.
Your Java program can monitor this file for changes, and then process the data it receives.

Printing from a batch Java job

Have done some research into this topic, but found no relevant answers. What I need is to print a number of PDF files on one of three forms, which are loaded into different trays of a particular printer. I need to specify which printer to use and it's not the default printer. Additionally, I need to specify which tray to use based upon an attribute of each PDF file and be able to switch between them at run time. Java PrintService seems to only be interested in the local default printer. I'd appreciate any suggestions on how to accomplish this task. Thanks.

The Printer API does allow for talking to different printers other than the default. That being said it is limited. What we did in our shop is to write a JNI layer that talks directly to the Print Queue of Windows and we use that. If you want finer control than the PrintService API provides you will need to write a JNI layer and access that from Java.

You could configure a different printer for each tray in your OS, Then print to that printer depending on the properties of your file.

Thanks for all the suggestions, but I think I have worked this out now. I'm using LPR for the printing and org.apache.commons.net.ftp.FTPClient for the tray switching commands. The actual tray commands are in text files. My tests (so far) have been successful and I did not have to install the printer on my workstation.