I would like to raise an exception class defined in Ruby from Java code. How would one do this?

The examples given in https://github.com/jruby/jruby/wiki/JRuby-Reference#Exceptions all show how to work with Java exceptions, but I would like to raise a Ruby exception.

We have this code:

    try {
      string = (RubyString) value;
    } catch (ClassCastException e) {
      throw context.runtime.newArgumentError(e.toString());
    }

I tried:

        RubyClass cls = this.runTime.getClass("Mongo::GssapiNative::Error");
        RubyString msg = RubyString.newString(context.runtime, message);
        throw cls.newInstance(context, msg, Block.NULL_BLOCK);

This failed with:

src/main/org/mongodb/sasl/GSSAPIAuthenticator.java:141: error: incompatible types: IRubyObject cannot be converted to Throwable
        throw cls.newInstance(context, msg, Block.NULL_BLOCK);
                             ^

So I need to convert my Ruby class instance to a Throwable?

Related question: our existing code supports exception causes, how do I attach those to Ruby exception classes? Is this handled for me automatically somehow?

Thanks in advance.