I recommend the following reference material to developers who would like to contribute to SimpleJTA.
Distributed TP - The XA specification
- This is the basic reference for how XA transactions are supposed to work. Although it describes a C api, it is pretty relevant because the Java XA specification is merely a wrapper for this.
Java Transaction API (JTA) Specification
- This is the reference documentation for JTA. My personal view is that the documentation is inadequate and one has to refer to the XA Specification to get clarity on many points. The vagueness of the JTA documentation is one reason why JTA implementations are so poor in quality.