Call my own Java code from C#

Question

Having my own Java code I'm using C# to call some unmanaged code that call (via JNI) the java code. I'm using JNI since I need to ensure:

• the ability that the Java code will run over real JVM and not over some .NET VM
• the ability to attach to the VM for debugging (IKVM does'nt support it)
• I need free solution
• The current free solutions are not applicable (e.g. IKVM)

Anyway, my question is how can I manage strings passed between these layers in the best manner without leaks. I'm doing something like:

[DllImport(@"MyDll.dll")]
public extern static void receive_message(string receDest, StringBuilder response);

This means I'm allocating the memory for the response in the managed code. I want to avoid that since I don't know in advance the response length. How can I write a JNI appropriate method that will allocate the right buffer for the managed code without leaks. The JNI code should be thread safe.

Any suggestions?

Thanks,

Guy

Answer 1

You may need JNI, but your requirements don't really indicate it.

The requirement to use a real JVM does not dictate the use of JNI. I'd suggest sharpening your requirements, or considering looser coupling. For example, socket comms, web services, a shared database, a shared file, or a queue.

If you really need Java and .NET to be run in the same process, with tight coupling, consider JNBridge.
They've solved the problem you are confronting.

Answer 2

You might be interested in trying to convert your Java bytecode code in .NET CIL with IKVM.NET.

Answer 3

You essentially need to make a remote call into the java program from your .NET-code.

With your current skillset I would suggest that you create a web service in the Java machine - this is relatively easy in Java 6 - and based on the WSDL create a client in your .NET program.

This is probably the cleanest solution with todays technologies.

If that for some reason isn't good enough, then add to your question.

Answer 4

I think you could use jni4net as a bridge library. Or you could just look at source code and grab some ideas (LGPL/GPL).

Answer 5

Guy -- Regarding Cheeso's response, and your respones to it:

• JNBridgePro does allow the JVM to be started automatically and run inside the .NET process (in addition to the option of starting it explicitly). See the "shared-memory" communications mechanism discussed in the documentation.

• JNBridgePro does allow you to attach a Java debugger, even when the JVM is running inside the .NET process. Contact [email protected] for details, as well as for details on configuring the JVM.

• Can't do much about it not being free, but it might be worth your while to check it out anyway.

Disclosure: Yes, I am with JNBridge.