How to run ferret (acts_as_ferret) with jruby?

I have an existing project, which uses the "acts_as_ferret" gem.

I installed it (and the other required gems) and tried to run the db-migration script.

I get the following error:

gems/rails-2.3.4/lib/rails/gem_dependency.rb:119:Warning: Gem::Dependency#version_requirements is deprecated and will be removed on or after August 2010.  Use #requirement
no such file to load -- ferret

and at the end:

script/server:4
Missing these required g开发者_JS百科ems:
  acts_as_ferret  = 0.4.4

when I list my gems, acts as ferret is listed. I assume it has something to do with ferret, which I am not able to install because I use jruby. (I get a native Extension Error)

How do I solve this problem? Thanks.