include Spring

I've gotten a little farther with my JRuby on Rails Spring integration code. I think I have what may make the beginning of a Spring plugin for JRuby on Rails. Here's the code for the Spring module. This is my first foray into metaprogramming in Ruby, I'd welcome any feedback.

# spring.rb
# June 20, 2007
#


module Spring
  include Java
  import javax.servlet.ServletContext
  import org.springframework.web.context.WebApplicationContext
  import org.springframework.web.context.support.WebApplicationContextUtils
  
  def spring_bean (bean)
    class_eval "def #{bean.to_s}; application_context.get_bean(\"#{bean.to_s}\"); end;" 
  end
  
  # dunno if there is a better way to do this.  I need the spring_bean method
  # to become a class method on the includee, but application_context needs to be
  # a normal instance method
  def self.append_features(includee)
    includee.extend(Spring)
    includee.class_eval do
      def application_context
        WebApplicationContextUtils.getWebApplicationContext($servlet_context)
      end      
    end
  end
end

This gives you a handy spring_bean method in any class where you've included Spring. The spring_bean method will then dynamically add an accessor to the class you use it in. This is what it looks like in a controller:

class TestSpringController < ApplicationController
 include Spring
 spring_bean :descriptor1
 def showcontext  
   render_text descriptor1.displayName
 end

end

Obviously to have this working you need several things. You need to have the goldspike plugin (from SVN trunk as per my earlier post). You also need to have Spring and its dependent jars in your WEB-INF/lib. I just copied em in for playing around purposes, with a little tweaking of my conf/war.rb file I could probably make goldspike fetch them. And lastly, it assumes you have an applicationContext.xml in WEB-INF, and that you have the Spring ContextLoaderListener declared in your web.xml.

Wow, that's a lot of trouble, why the heck would I want to do all that? What's this all for anyways? First of all, if you need this you probably don't need to ask, you know who you are. No, I'm not even trying to suggest using Spring for greenfield JRuby on Rails applications. But if you need to do heavy Java integration or you have an existing Spring application you want to front end in Rails, this kind of thing could end up being quite handy. This is my situation: I have a pretty large Spring/Hibernate/Tapestry app and I'd like to make moving to JRuby on Rails a viable option. Rather than replace everything whole hog, I'd like to be able to leverage working Spring services easily from Rails. As you can see, doing this should be a piece of cake.

Spring + JRuby on Rails

I've only been threatening to do this for a year, but I finally added the necessary stuff to have JRuby on Rails talking to Spring. There's a lot more to come here, but this controller code demonstrates being able to get ahold of a Spring WebApplicationContext in a Ruby on Rails controller.

class TestservletController < ApplicationController
  include Java
  import javax.servlet.ServletContext
  import org.springframework.web.context.WebApplicationContext
  import org.springframework.web.context.support.WebApplicationContextUtils
  
  def showcontext
    app_context = WebApplicationContextUtils.getWebApplicationContext($servlet_context)
    render_text app_context.display_name
  end
end

In order for this to work, you'll have to use the very latest goldspike-snapshot plugin from SVN trunk. I just checked in the code to expose $servlet_context earlier today. Obviously this code will only work using a servlet container, and you'll need to have Spring and necessary deps in WEB-INF/lib and have the Spring context loader listener in your web.xml. From here, my next step is some metaprogramming to allow you to add spring bean accessors into your controllers.