[Discourse.ros.org] [Client Libraries/rosjava] Is rosjava worth using when not using android

[Michael McConnell]

msmcconnell June 16

My team will be starting a large ros project soon. Much of our non-ROS legacy code is written in Java and we are debating how best to integrate ROS. I have some questions which would be helpful in making a decision. What is the usability of rosjava for large projects? It seems to still be in development and has been updated to kinetic, but much of the documentation and discussion around it seems to be a couple of years old. Would anyone recommend it for projects that don't involve android development? Is there a substantial performance impact from using rosjava vs ros-native? Is communication between a rosjava node and a ros-native node difficult? Also does it support tf2? I realize this is quite a bit to ask in one question, but I hope someone can help.

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[Juan Ignacio Ubeira]

jubeira June 16

Hi @msmcconnell!
Let me try to answer your questions the best I can:
- Rosjava can be used "as is" in a real project. I'm using it myself in a project where roscpp and rospy are not an option, and it does its job. The documentation in the wiki should be good enough to get started, and I offer myself to help to improve it if necessary.
It has some issues as you can see in its public repository, but its currently under active maintenance: if you find something that is wrong, or want to contribute a new feature, you will get a response within a short time lapse.
- I don't have an accurate answer about its performance; it will probably depend on what you want to do. What is your application about? My short answer would be that you shouldn't have problems with it (see next item).
- You can write native nodes and execute them from a java application if you want; Rosjava kinetic has support for that. I've tried it and it can be done. You can take a look here: http://wiki.ros.org/android_ndk/Tutorials/WrappingNativeRosjavaNode. (The link is under Android, but it can be done for pure java). Then, nodes can communicate through topics as usual in ROS. From the java side of the application, all the nodes have the same interface, so you don't care if the node's implementation is in Java or in native code when you execute it (does this answer your question?).
- TF2 messages are included in rosjava messages (here's the Maven artifact: https://github.com/rosjava/rosjava_mvn_repo/tree/master/org/ros/rosjava_messages/tf2_msgs).

Hope this helps! Don't hesitate to ask again if you need any clarification about anything.

[Michael McConnell]

msmcconnell June 16

Hello @jubeira,
Thank you so much for the detailed response! This has definitely cleared up most of my questions. I imagine performance won't be an issue since we can wrap native nodes. I'm going to start experimenting with rosjava a bit more, now that I know it is worth looking into. I'll let you know if I have any more questions. Thanks again for the great answer!

[Juan Ignacio Ubeira]

jubeira June 16

Awesome, good luck with that!
I will try to help you whenever possible, just let me know!

[Christian Mock]

Christian_Mock June 17

Can I use rosjava at my OSX without installing some ros-related installations ?
ROS OSX did not install and is no option at OSX Sierra :frowning:

Thanks for some suggestions
Cheers
Chrimo

[jcerruti]

jcerruti June 19

Christian,

Yes, that would work. Rosjava is a pure Java implementation.
Note that the available functionality is highly reduced compared to the core client libraries, but you would definitely be able to create nodes and connect to other ROS systems

[Michael McConnell]

msmcconnell June 26

I have another question. Is there an implementation of any tf2 functions beyond the messages. The Maven artifact you posted works well for creating tf2 messages, but I haven't been able to find any information on an implementation of the rest of the tf2 libraries. Have tf2 classes such as the transform broadcaster been ported/wrapped?

[Juan Ignacio Ubeira]

jubeira June 26

I've never worked with tf2 in depth, but a transform broadcaster or static broadcaster is not hard to implement: it's pretty much a node that publishes tf2 messages. There are also some helper classes around to handle geometry transformations and stuff like that.
Another option would be to use a cross compiled version of the Cpp library, but I'd only do that if the library you need is too complicated to implement in Java (for a simple publisher, I think it's not the case).

Perhaps if you open a concrete thread in ROS Answers I can be more helpful. Please point me to the link if you do so!

[Michael McConnell]

msmcconnell June 27

Ok. I am looking into implementing the transform broadcaster. It looks like it should be doable. I'll update after I give it a shot.

[jcerruti]

jcerruti June 27

That's great! Good luck and feel free to PR your contribution to the rosjava repo. We'll try to review and accept it quickly.

[Michael McConnell]

msmcconnell June 28

After digging into the structure of tf2 more I decided there was not much value in recreating the transform broadcaster. In order to fully utilize tf2 much of the library needs to be recompiled with JNI wrappers. This was done for RosTango 3 years ago, but has not since been maintained. I came across the FrameTransformTree in the ros_geometry package. This tree is compatible with tf2 and provides the same basic query functionality. This can be used with a simple subscriber setup to maintain the transforms from the /tf topic while still using tf2 tools for visualization etc.