Using Mahout from JRuby raises "missing class or uppercase package name" for some classes

Question

I'm attempting to use Mahout in JRuby by requiring the following three JAR files from the latest stable Mahout distribution.

• mahout-core-0.9.jar
• mahout-integration-0.9.jar
• mahout-math-0.9.jar

Some of the classes I'm trying to use work fine, but some in particular aren't loading. Instead I get exceptions like this one:

NameError: missing class or uppercase package name (`org.apache.mahout.cf.taste.impl.recommender.GenericBooleanPrefUserBasedRecommender')
  get_proxy_or_package_under_package at org/jruby/javasupport/JavaUtilities.java:54
                      method_missing at file:/Users/bloudermilk/.rbenv/versions/jruby-1.7.10/lib/jruby.jar!/jruby/java/java_package_module_template.rb:14
                              (root) at _test.rb:9

I'm sure that the class exists in the package, as it is mentioned in the docs. In fact I can also decompress the mahout-core JAR and see the respective .class file in there.

I uploaded a test repo to GitHub here: https://gist.github.com/bloudermilk/8832036

I don't have any Java experience so it seems likely I'm missing something obvious. Why isn't JRuby able to find this class? How can I remedy this?

Answer 1

When I tried this, I got an error like:

Java::OrgApacheMahoutCfTasteImplRecommender::GenericBooleanPrefUserBasedRecommender
NameError: cannot link Java class org.apache.mahout.cf.taste.impl.recommender.GenericBooleanPrefUserBasedRecommender, probable missing dependency:

My guess is that you don't have something on your classpath. I took the "big hammer" approach to get everything on the classpath and was able to get it to work:

Dir['./mahout/*jar'].each {|f| require f}
Dir['./mahout/lib/*jar'].each {|f| require f}
Java::OrgApacheMahoutCfTasteImplRecommender::GenericBooleanPrefUserBasedRecommender