We're trying to determine how to implement a simple plugin framework for a service we are implementing that allows different types of calculators to be "plugged-in".
After reading a number of posts about Java plugin frameworks, it seems like the most common options are:
OSGI seems to be more than we need.
"Rolling your own" is ok but it would be nice to reuse a common library.
So we're down to the JPF and JSPF. JPF doesn't seem to be in active development anymore.
JSPF seems very simple and really all we need. However I haven't heard much about it. I've only seen one post on StackOverflow about it. Does anyone else have any experience with JSPF? Or any other comments on this design choice?
Update: There isn't necessarily a correct answer to this.. however we're going to go with Pavol's idea as we need just a really, really simple solution. Thanks EoH for the nice guide.
If you are planning to have just one (or only a few) not very complex 'extension points' than perhaps a well-defined SPI and a piece of configuration might be sufficient. No need to use a plugin framework.
By piece of configuration I mean some mechanism to find your plugins. For example something like META-INF/services/ or simply listing your plugins in a configuration file.
More details (upon request):
SPI = Service Provider Interface, an "implementer-side equivalent of an API". To learn more try searching for a difference between API and SPI. However in this context it is just a fancy term for an interface to be implemented by your plugins (i.e. defines the contract for your plugins).
A nice, short article "Creating a Service Provider Interface" by Ethan Nicholas describes how to create your own SPI in similar way as it is done in several part of the Java Platform itself.
META-INF/services/ can be seen as a more generalized approach to creating SPIs. More information can be found in the respective section of the JAR File Specification.