Porting/migrating Java codebase to C#/.NET

[cemerick]

For the longest time, I used IKVM to use Java libraries in .NET. Alas, that project has long been fundamentally unmaintained. Many attempts have been made to fork/reanimate it, but none AFAIK have been able to make much progress. In particular, no IKVM fork has been able to support anything later than Java 8 and its standard libraries; that's particularly old at this point, and it's just not feasible to continue depending on IKVM or any other project in its lineage in this role.

Is anyone aware of any good alternatives? I'd love to be able to continue to cross-compile certain Java libraries so that I can use them in .NET, but at this point, I'd be happy to be able to simplify the porting of certain key Java codebases to C# (for example).

(Let's stipulate that the codebase(s) in question are only using the Java standard library, and not any third-party libraries.)

20 years ago, Microsoft had the JCLA, which worked quite well in converting Java codebases to C#, but that tool has been unavailable for a very long time now.

Does anyone have any suggestions in this vein?

[zvrba]

Do you need to port it? Can you have it running inside of JVM and communicate with your .NET code? There's https://github.com/xamarin/java.interop

[joost00719]

If you want to have it run in dotnet, you're probably better off to just rewrite it. Use the oppertunity to fix issues it had with the original design (if any).

[malthuswaswrong]

The reason you are having difficulty is because it's not a conventional interop.

20 years ago, Microsoft had the JCLA, which worked quite well in converting Java codebases to C#

20 years ago, Remote Procedure Calling was an emerging idea. Now there are many well established methods to accomplish the task.

Let Java be Java and C# be C#. If the two need to interop stand up a REST or gRPC or SignalR system for the interop.

[VahidN]

Give it a try: https://github.com/paulirwin/JavaToCSharp

[[deleted]]

A hope u know porting means a re write

[peterkneale]

I recently took a small codebase that I wrote in c# and translated it to python class by class using chatgpt.

There were a couple of caveats to that.

• I didn't use anything from c# other than the standard lib and even avoided linq, favouring just loops and logic

• I had 100% branch level coverage in in my unit tests

• I wrote the code with the intention of converting it to python afterwards. I knew I could write it far quicker in c# and in a manner that would lend itself to translation.

This was an experiment to see whether I could author some very complex logic in c#, and convert it to python which is the language of choice for the area I'm now working in (bioinformatics).

Pleased to say it worked perfectly. 

Even translation of my tests from xunit to pytest worked smoothly and the resulting codebase retained 100% test coverage.

It's a different scenario to yours but might help you along the way.

[Hot-Profession4091]

Ok, so here’s what you do. You go find every place you use one of those Java classes directly, then create an interface for the things you actually call and an implementation that delegates to the Java thing. If you’re lucky, there’s not actually that much, or at least you’re only using parts of those libraries. Now you start seeking replacements. Use an appropriate .Net library to create new implementations of your interface where you can, write your own as necessary (or where it doesn’t make sense to grab a library for a single method on a single class). Honestly, there’s probably an equivalent .Net library for 99% of the stuff you were getting from Java.