Open source of provided librairies



Hi again MicroEJ team,

In the FAQ ([Debugging] Most methods implementations consist of “throw new RuntimeException()” statement) I see that most libraries come with NO source code.
Do you plan to release the source code in order to help debug ?

Best Regards


Hi again John,

Most of the foundation libraries (the core runtime) do not have public sources [1]. However the add-on ones have [2]. We also tend to deliver the sources of the foundation libraries to our partners for debugging.

Hope it’ll help.



Dear Mister Harel,
Does MicroEJ plan to deliver the source for foundation libraries too ? From your link [] I assume that most of the source comes from OpenJDK source code, using the [GNU classpath exception] that enables modifications and distributions of the source code (therefore there is little gain to keep the source secret) ?
If you plan to open source the foundation libraries, do you have a roadmap due date ?

Looking forward reading you
Best Regards


Hi John,

There is no legal issue with the source delivery of MicroEJ Libraries.
As previously explained in this post, Add-On Libraries are already delivered with the full source code and the legal licence (e.g.

For Foundation Libraries, here is what is currently planned for MicroEJ 4.2:

  • Foundation Libraries APIs will still be delivered with empty skeletons, as they have a dedicated life-cycle.
  • Foundation Libraries Implementations will be rebuilt to embed the sources in MicroEJ 4.2 Architectures.
  • In MicroEJ SDK, when debugging an application, the sources provided by the Platform will be displayed in place of API empty skeletons.



Thanks a lot for your detailed answer. I am transmitting to my colleagues such a very good news of having ALL MicroEJ libraries being distributed in Open Source soon.

Looking forward to using MicroEJ VEE on our next generation of wearable soon.