Problem / Scenario:
You have server code in Java implementing business logic, or you want to have such code. Java is your strategic choice.
But… you have a need for a client application that will be a native Windows application, for whatever reason. Sample reasons: (1) they need to run quickly and smoothly on a factory floor full of Pentium 150 or slower machines with limited RAM. (2) they need to work in disconnected mode, or talk to local hardware, so a web application won’t work.
How do you write server code in Java (in EJBs, for example) but access it easily from a native Windows clients, for example a Delphi application?
Solution #1: Talk JRMP from Delphi
Implement the Java RMI JRMP protocol in Delphi. This will be nearly impossible, since it is built on Java object serialization. So there are various approaches you could take.
Solution #2: Java on the Client, use JNI
Run Java on the client as well, and use JNI to communicate between Delphi and Java, then Java to do the client side RMI. This defeated the goal of keeping the client lean, though… a Delphi thin client can run well on an old, slow machine with 32 meg of RAM, Java can’t.
Solution #3: RMI-IIOP / CORBA
Some Java application servers can seamlessly (?) expose Java services (like EJBs) as CORBA objects. Borland has CORBA support available for Delphi. This will avoid the overhead of Java on the client, but is too vendor-specific for my tastes.
Solution #4: Your own Proxy on the server
Use a non-RMI way to communicate between the Delphi client and an extra "tier" at the server; this piece of middleware would communicate with Delphi using any of a number of methods, including DCOM. Then use JNI or other means to access the Java services on the same (server) machine.
Solution #5: ASTA-Java
ASTA has a product (though I don’t know if it’s in development, or ready to go) that provide an generic mechanism for invoking EJB operations, from a Delphi client. The challenge here is how to send and receive complex types, which are defined by Java classes.
Solution #6: Web Services with SOAP
Expose the server-side services as web services via SOAP. Choose an application server which will automatically expose your EJBs this way, if possible. Then use any available way to make a Delphi client talk SOAP. PureSOAP and Microsoft’s SOAP support are two possible ways. (This is really the most appealing choice to me, as of 2001.)
Solution #7: Homegrown web services
It’s really not all that hard to write wrapper code that exposes your server services via HTTP requests with parameters, via XML strings, etc. Such a thing would not be language specific, so the server could be on one language, the client in another. This solution has some appeal in cases where you want the pieces to be tightly "wrapped up" and not exposes in anything as standard as SOAP for some reason.
There many, many paths to use to get from point A to point B… if you have a different scenariou in mind, tell me about it and I will try to expand this page to cover it.
Need to do this for your own project? Consulting services are available.