I'm finding the same issue with 9.0.0.0.rc1 also. Your simple test case illustrates it well. It looks like you're using rvm or rbenv to launch jruby. I'm invoking it from jruby-complete.jar and getting the same result.

Trying to use "java_import" the ruby classes results in an error like:

NameError: cannot load Java class test

Even if I rename the input file "Test.rb" with a capital "T", and it generates a java class called "Test", I still get the error:

NameError: cannot load Java class Test

$ javap Test.class
Compiled from "Test.rb"
public class Test {
  public static void main(java.lang.String[]);
}

By the way, have you noticed how much cleaner the compiled classes are? Version 1.7.20 produces class files that look like this:

$ javap Test.class
Compiled from "Test.rb"
public class Test extends org.jruby.ast.executable.AbstractScript {
  public Test();
  public static org.jruby.runtime.builtin.IRubyObject __file__(Test, org.jruby.runtime.ThreadContext, org.jruby.runtime.builtin.IRubyObject, org.jruby.runtime.builtin.IRubyObject[], org.jruby.runtime.Block);
  public org.jruby.runtime.builtin.IRubyObject __file__(org.jruby.runtime.ThreadContext, org.jruby.runtime.builtin.IRubyObject, org.jruby.runtime.builtin.IRubyObject[], org.jruby.runtime.Block);
  public org.jruby.runtime.builtin.IRubyObject load(org.jruby.runtime.ThreadContext, org.jruby.runtime.builtin.IRubyObject, boolean);
  public static void main(java.lang.String[]);
}

Ok, this is fixed now for RC2. There's one caveat, however...

In order to speed load times, we have removed .class from load searching by default. In order to have JRuby search for .class, you'll need to pass -Xaot.loadClasses=true to JRuby or -Djruby.aot.loadClasses=true to the JVM. This probably needs to change in warbler or jruby-rack somewhere (what do you think, @kares?)

JRuby-Rack should be fine ... but Warbler might be affected by the .class loading change // cc @jkutner

With a quick warbler test, it looks like this fixes the problem (without the aot.loadClasses=true). I'll investigate further to make sure that's right, but I don't expect any difficulty. Thanks @headius!

I am bumping into this issue and I am packaging with warbler on 9.2.0.0

I tried passing this -Djruby.aot.loadClasses=true but the jvm rejected i.e. 1.8.0_171

I've opened up a new ticket since this one is closed and doesn't appear to be seen. See #5341 for similar issue in 9.2.0.0