Implementing Excel Function in POI API

How can I implemen开发者_开发技巧t an unimplemented Excel function in the POI API without recreating the jars to change the FunctionEval class and possibly some other classes?

Can I just create a function and register it somehow?

Depends on what kind of formula function you're adding

For User Defined Functions, you can register them. See the User Defined Functions page for details on both writing them and registering them

For regular built in functions which are missing / not implemented, your best bet is to knock up a implementation and submit it as a patch to be included in POI itself :)

For some more details on writing functions, and how it all works, see this talk that was given at ApacheCon last year.