Using C# to serialize a Java deserializable object

Question

I have two application that need to talk to each other. App1 needs to be able to serialize an object that App2 can then deserialize. Easily done, right? Here's the problem; App1 is C# based, App2 is Java based. So App1 needs to write out the file in the Java binary file format. How can this be done?

The way I see it, I have two options. The first is figure out some way to serialize a Java object in C#, so that App1 just creates the appropriate file. My other option would be to write a converter in Java that reads in a file and populates the object accordingly and serializes the newly populated object. That way the C# app would only have to write out some sort of formatted text file that the converter then interprets.

I can't make any changes to the Java application.

How should this be done?

Update:

The Java application is already in the hands of customers so changing the serialization scheme would cause the customers existing data to be incompatible. The Java App uses the native java serialization when dealing with this object. Modifications to the Java app can't happen.

The C# app uses protocol buffers to serialize its own data.

Answer 1

Your best bet would be to write something that uses Java Native interface. Not fun, but it'll work.

You can do this directly using JNI (not fun but doable) or there may be some tools out there that will generate code for you -- take a look at SWIG: http://www.swig.org/

You would call Java from C# to do the persistence for you.

Answer 2

Just use XML serialization. Both frameworks have good support, and the simplicity will make it easier to debug / maintain. Write a small program in Java that just imports the XML and writes the binary file.

Answer 3

"IKVM" might be something you could use. This product allows you to convert compiled java bytecode (.jar, etc.) into a .NET DLL. It's super easy to use, and might give you the interop you need.

Other than this, the easiest way to accomplish this without a binary-level interop is to just use a plain text format, such as a CSV or XML.

Answer 4

The best answer is option 3: use a language-neutral serialization scheme.

I use JavaScript. Thrift is another option, protocol buffers I believe are more focused on RPC, but should be usable for serialization as well. XML or a custom binary format would be other options.

Edit: Sorry, didn't notice that you can't make changes to the Java application. That said, the best way to do it would probably be to create your own well defined format, write a java app that can read that format, then output a serialized java object for the legacy app.