Thursday, June 21, 2007

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.

10 comments:

dacc said...

Nice work, and very useful. =)

Thanks for posting the details.

El Raichu said...

i think the recommended way of extending is through self.included base instead of self.append_features base (even though rails uses #append_features instead of #included).

Thomas Enebo said...

You can probably take this a step further and have the first reference to spring bean method redefine itself so it does not need to go through application_context.get_bean() every time. Not sure it would make a big difference, but it is an option.

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