xperienced web developers know well how many layers of conversion they have to go through to present persistent information to the user:
- Mapping web requests to executing code
- Converting objects to relational data
- Rendering markup from their object structures
Open source frameworks (particularly Spring and Hibernate) have become extremely good at easing the pain of these conversions, but that ease has come at a price: reams of XML configuration. On a typical web project using Spring and Hibernate, I spend a great deal of my time writing, updating, and debugging configuration files rather than implementing the valuable business logic I am paid to write.
Just imagine how much easier life would be if Spring knew where all your controllers were and Hibernate could find your domain objects all by themselves. Well, it turns out they can thanks to coding by convention, a development paradigm introduced by Ruby on Rails.
Coding by convention is at the heart of Grails, a rapid application development framework implemented in Groovy, a dynamic language that is syntactically similar to Java and runs in the Java Virtual Machine (JVM). Grails is implemented through a series of plugins. Each of these plugins is executed during application initialization and is able to register beans in the Spring ApplicationContext. There is a plugin to configure Hibernate, another plugin to tell Spring and Hibernate that all classes in the domain directory can be persisted to the database, another plugin to register all classes under the controllers directory as Spring controllers, and so on.
This article shows the power of Grails through the practical example of building a blog application. It does not cover Groovy in any depth, rather, it providing explanations only of the particular Groovy syntax that is used in the example. Simply put, Groovy can make calls to Java classes directly, so if you put your Groovy code in the right place, Grails does the rest.
Go to your development workspace and run this in the command prompt:
grails create-app groovypublish
This will create a folder called groovypublish and a grails-app directory under that, which contains the following directories:
This article concentrates on the controllers, domain, and views folders. If you are familiar with the Model View Controller (MVC) pattern, you can figure out what goes in each of these directories, but they will be introduced in more detail as the example progresses.