How to get issue's and project's SLA data with JAVA API

Hello everyone!
Can someone help me to understand how to work with JSD internal classes and interfaces?
As I know, JSD SLA classes mostly undocummented, so there is no support from Atlassian.
But some plugin developers uses these classes (Adaptivist etc).
So maybe someone can share a little bit info?
I want to use this API in groovy scripts