How to programmatically import plugins and fragments from jar files

I have some plugins and snippets exported to some jar files. I need to programmatically import these plugins and fragments, as is usually done using the graphical interface, using File --> Import --> Plug-in Development --> Plug-ins and Fragments, so I have this in my current workspace. I read a few posts related to import projects (i.e. Using .project), but in this case I only have jar files.

Snippets and / or tips will be really appreciated.