Tuesday, May 26, 2009

Groovy on Grails

Grails is a web application framework build on top of well known languages, frameworks and libraries. It uses the Groovy programming language which gives it power because of it's dynamic nature. Under the hoods, Grails uses Spring framework(for MVC), Hibernate (for OR mapping), Quartz (for scheduling), Log4J (for logging), JUnit for unit testing, and Canoo Webtest for functional testing.

We already have a Gazillion frameworks, do we need Grails ?

Typically web development in Java is a very long and arduous process. When a web project is started, many configuration files have to be set up after which the project development begins. Even then we have to create domain objects, basic controller functionality, the model, stylesheets, views, and other aspects of business logic. Grails makes things easier by allowing us to do all of these things rapidly and in fewer lines of code. So how does Grails allow us to do all this with fewer lines of code? Grails uses convention over configuration.

If you have developed a JEE app with Struts, you probably remember configuring struts-config.xml to map ActionBeans, Actions, Action classes, Global forwards, and so on. A typical development workflow with Struts is as follows:

  1. Create struts-config
  2. Create ActionBean classes and write their validators
  3. Create Action classes and delegate persistence and other things to model classes
  4. Create a Hibernate configuration file
  5. Create views with JSP's using Taglibs
  6. Write unit tests (these two are not really the last two... remember TDD)
  7. Write functional tests

Whew.... isn't that a lot of work to do? In Java I have always felt like there is just a lot of coding and configuration that needs to be done to make even the smallest web application.

Grails takes away a lot of this pain. This means we do not have to specify and code the smallest of things if we follow certain conventions. We however have the ability to break the conventions if we want to (in case of integrating with legacy databases, etc) by adding configuration.

So, for example lets assume we want to make a simple application to manage a music collection. We start with creating a Grails app with a grails command, after which we create a domain class. Thats it. Grails will scaffold the application for us, meaning it will create the entire infrastructure to give basic CRUD functionality with our domain object (this includes the controller, and views for adding, deleting, updating, and modifying data). So within minutes we have something we can use. Off course in most situations we will not want something as simple as this. We will have to extend the application in various ways. But I suspect, even after extending the application we will still have saved some time by using Grails, and there is another benefit. Because Grails gives us something really quickly, we can use the Agile approach where we quick feedback on what we are trying to accomplish, and every feedback loop actually gives us something that is usable and .

Because Grails is written in Groovy which is a JVM language, we can take advantage of all the Java libraries that we have become familiar with and also gain benefits from the JVM's optimizations.

A few other features of Grails which I have noticed and like are:

  1. Ability to upgrade to a newer version of Grails with a single command
  2. Automated creating of test classes (thus prodding you to write unit tests)
  3. Ability to use different databases for testing, development and deployment
  4. Command for creating domain objects, and controllers
  5. Inbuilt UI templating
  6. Host of third party plugins that extend the Grails framework
  7. Extremely simple mechanism to create Tag libraries
These are some of the features that I have read about, but I am sure there are many more.

If you build web applications in Java, Grails is definitely be something you should look into.

More about Grails coming up in future posts.

1 comment:

Anonymous said...

Grails uses Sitemesh for layout rendering on the front end.