GR8Conf 2009. The Grails Plugin System by Graeme Rocher

Grails Plugins

Modularizing your application with
Plugins

Copyright 2008 SpringSource. Copying, publishing or distributing without express written permission is prohibited.

Objectives

• Understand the basics of the Grails plugin
system
• Explore how to create modular applications
through plugins
• Unlock the potential of Convention over
Configuration

Copyright 2008 SpringSource. Copying, publishing or distributing without express written permission is prohibited. 2

Agenda

• Plugin basics
• Creating, packaging and installing plugins
• Building functional plugins
• Automating configuration
• Enhancing behavior


The Background

• Grails is designed to wire
together different libraries
and make them easy to use
• In this sense it can be seen
as a "platform for runtime
configuration"
• De-coupling those
components was hard
without a well defined
system

The Plugin Architecture


The Extension Points

• Build System
• Spring Application Context
• Dynamic method
registration
• Auto Reloading
• Container Config (web.xml)
• Adding new Artefacts


What is a Plugin?

• Just like a normal Grails
project!
• The only difference is the
presence of a
*GrailsPlugin.groovy file
• Use grails create-plugin
to create one!


Creating and Running a
Plugin

• A plugin is just a regular Grails project
and can be developed like one:

$ grails create-plugin blog

$ cd ../blog

$ grails run-app


A Plugin Project

A Plugin project is the
same as a regular Grails
project except it has a
special plugin Groovy


The Plugin Descriptor

class LoggingGrailsPlugin {

def version = 0.4
def dependsOn = [core:"1.0 > *"]

... Plug-in
Dependencies
The Plugin Version
}


Packaging & Installation

• Installation of Grails plugins can then be
achieved with a few simple commands:

$ grails package-plugin

$ cd ../my-project
$ grails install-plugin
../logging/grails-blog-0.4.zip
// or remotely
$ grails install-plugin http://myserver/
grails-blog-0.4.zip


Plugins & Application
Modularity
Messaging Security Search
Plugin Plugin Plugin

Grails
Application

Blog Wiki Maps
Plugin Plugin Plugin


Adding Basic Artefacts

• A Plugin can add new tag libraries,
controllers and services simply by
creating them in the plugin project
• Since a plugin project is just like any
project you can run and debug a
plugin in its own project before
distributing it
• Once you're done package and
distribute it!


Demo

Building a Functional Plugin


Automating Configuration
import org.springframework.cache.ehcache.*
import grails.util.*
Implement ‘doWithSpring’
to modify Spring context
def doWithSpring = {

blogCache(EhCacheFactoryBean) {
if(Environment.current ==
Environment.PRODUCTION) {
timeToLive = 2400
} Sets the “timeToLive” of
} the cache for
Configures a Spring production only
bean called “blogCache”

Automating Configuration

• Plugins allow you to manipulate the underlying
Spring context based on:
– The Environment
– The Conventions
– The State of other Plugins
• Simply implement the doWithSpring plugin
hook
• See the user guide for a description of the
Spring Domain Specific Langauge (DSL)


Enhancing Behavior
def doWithDynamicMethods = { ApplicationContext ctx ->
application.domainClasses.each { domainClass ->
domainClass.metaClass.constructor = {->
ctx.getBean("Bookmark")
} Support auto-wiring from
Spring in regular constructors!
// adds a new Foo.load(21) method
def template =
new HibernateTemplate(ctx.getBean("sessionFactory"))

domainClass.metaClass.static.load = {Long id->
template.load(delegate.getClass(), id)
}
}
} Interact with the
Hibernate session!17

Enhancing Behavior

• Plugins can add new methods and APIs using
metaprogramming techniques
• Simply implement the doWithSpring plugin
hook
• See the metaprogramming guide on Groovy’s
website: http://groovy.codehaus.org/
Dynamic+Groovy
• Huge number of possibilities are opened up
via plugins


What plugins enable...



• Test Grails: selenium,
fitnesse, code coverage etc.



• Rich Grails: Flex, GWT,
GrailsUI (YahooUI) etc.



• Secure Grails: Spring
Security, JSecurity, OpenID
etc.



• Secure Grails: Spring
Security, JSecurity, OpenID
etc.
• Integrate Grails: Search,
Jasper Reports, JMS etc,


The Plugin Portal
• http://grails.org/


Summary

• Plugins are crucial the the Grails story
• Everyone is a plugin developer, not just
the gurus
• Plugins help create modular applications
• Plugin automate configuration through
Convention over Configuration


Q&A


GR8Conf 2009. The Grails Plugin System by Graeme Rocher

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GR8Conf 2009. The Grails Plugin System by Graeme Rocher