Grails is an open source Web application framework written for Java platform. It is based on the Groovy programming language and is a competitor to Ruby on Rails.
Grails boost programmer productivity by eliminating configuration effort using the "coding by convention" paradigm.
Grails eliminates the need for downloading and configuring multiple sets of applications for starting development of a Java Web application. Grails provides a single package which contains test application server, ORM tool (Hibernate) etc. So in a nutshell, Grails is J2EE on steroids.
Books on Groovy
In order to be an expert on Grails, you need to learn Groovy. Groovy is a scripting language based on Java. Following are some of the good books available in Groovy.
Groovy in Action – This takes a detailed look at the Java scripting language Groovy. This is the favorite book on Groovy.
Groovy Recipes: Greasing the Wheels of Java– Groovy recipes one programming problem at a time and explores how it can be done in Groovy. This is a must have book if you want to be quickly productive in Groovy. This book also looks at Grails.
Programming Groovy: Dynamic Productivity for the Java Developer – This book is not yet released. This is intended for new programmers and will contain both Groovy fundamentals and advanced Groovy topics such as meta programming, unit testing and domain specific language creation.
Books on Grails
The Definitive Guide to Grails (Definitive Guide) – This is a comprehensive reference to Grails. It takes you through the complete Grails development lifecycle such as project configuration and automatic ORM mapping. This also contains a quick introduction to Groovy.
Getting Started with Grails – This book is available as a free Grails book download (PDF). This is a quick introduction to Grails platform. It takes you through the framework step by step. It also explores how a Web application is turned into concrete code from abstract code.