Using java (jar) libraries in go

[dpapathanasiou]

I'd like to use Titan Database[1] with go, but I could not find any
pre-existing drivers.

Titan is written in java, and is normally built with maven, producing
a jar library file[2] used by jvm languages.

If I wanted to write my own, what is the recommended approach?

Is there an equivalent of cgo for java jars?

[1] https://thinkaurelius.github.io/titan/
[2] https://github.com/thinkaurelius/titan/blob/titan10/BUILDING.md

[Justin Israel]

If you goal is just to communicate with a Titan Server, then I think all you need is a gremlin client, since its an abstraction layer over swappable graph database backends. I've not used this library, but a quick search shows a recent project for a gremlin client:

https://github.com/go-gremlin/gremlin

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[dpapathanasiou]

Thanks for the suggestion, that's a good idea.

I was thinking more in terms of a direct connection, though, especially
for smaller deployments where I don't have a full titan server running.

I did find this project, which takes advantage of the Java Native
Interface to use a C bridge, and finally cgo:

https://github.com/timob/jag

[Owen Tuz]

This is summed up on StackOverflow fairly well:
https://stackoverflow.com/questions/23872323/how-to-use-jar-file-in-golang

The short version is that the "simplest" (you'll see why that's in quotes in a second) approach would be to use cgo to call some C code, and use C's more tried-and-tested Java bindings to then call your Java library via the JNI.

For an example, you could look at this, sadly abandoned, Github repo where someone has done exactly that:
https://github.com/abneptis/GoJVM

I wouldn't really recommend it, however. It may be simpler to find another way to connect, or even to write your own drivers.

Cheers,

Owen

[Tim O'Brien]

Hi,

I'm the author of Jag, if you have relatively simple API on the Java side, it will generate a nice Go package to access it.

The Cgo code that uses JNI is in https://github.com/timob/gojvm. It is a fork from https://github.com/abneptis/GoJVM, it's in desperate need of some love, its old and crusty. I am taking another look at it with Go 1.5 Cgo changes, to see whether I should replace it, it won't effect the API of the package Jag generates.

Tim

[dpapathanasiou]

Thanks for that link, as well as the link to GoJVM; I'll study the source.

[dpapathanasiou]

Thanks! I'd be happy to start making pull requests once I wrap my mind around the concept.