Modello Java Mojo is marked as threadsafe, but is not

[cstamas]

The Modello Java Mojo (did not check others) is marked as threadsafe, but is not.

Proof: try to build maven-3.9.x branch with any of these: -T (either plain or smart builder) or mvnd, and Modello fails badly. Code generator is stateful singleton, and generated sources are not landing on desired place...

[gnodet]

Superseded by #415

[cstamas]

This issue is not solved by 2.2.0, tested locally. While the generators are made prototypes (non singletons), the 2 core components (managers) are still singletons, and the fact they inject Map<String, Generator> still makes generators singletons...

My test build with 2.2.0 still fails. My test build passes if I make non-singletons these:

• DefaultGeneratorPluginManager
• DefaultMetadataPluginManager