Grails Overview

  What is Grails and why should I care? 

  Building on Java’s strengths 

  The Groovy language 

  A tour of Grails 

  Ancillary tools useful in Grails 
© 2009 DevJam ‐ All rights reserved.

  Web application development environment  
  Built on the Java Platform 
  Groovy as the primary language 
  Java can also be used and intermixed with Groovy 
seamlessly 
  Favors Convention over Conﬁguration 
  Similar in spirit to Ruby on Rails 


  Java web development can be tedious 
  The JVM, class libraries, and frameworks are 
the real strength of the Java Platform 
  Groovy is an excellent dynamic language for 
the JVM 
  Compiles to Java bytecode (.class ﬁles) 
  Favor convention over conﬁguration 
  Grails is an opinionated framework 
  Enhances productivity 

  Built on top of the Java Virtual Machine 
  Maturity 
  Optimization and performance 
  Runtime familiarity  
  Integration with Java applications   
  Groovy classes are Java classes 
  Reuse what works from traditional Java stack 
▪  Java EE: Servlet API, JDBC, JMS  
▪  Hibernate, Spring Framework, Spring MVC, SiteMesh 

  Hibernate  
  Object/relational mapping (ORM) 
  Spring Framework 
  Dependency injection services 
  Application lifecycle facilities 
  Spring MVC 
  Web framework 
  SiteMesh  
  User interface layout and theming facilities 


  Grails convention dictates…  
  Where components reside in the application 
  How the component is named 
  How the component is wired and collaborates 
with other application components 
  How applications can be extended through the 
use of third‐party plugins 


  Standardized conﬁguration 
  Log4j, database datasources 
  Autowiring and dependency injection of 
components 
  Standardized build 
  Gant scripts 
  Standardized domain model 
  GORM facilities injected into domain objects 
  Standardized services 
  Automatic transaction support  

  Features inspired from Python, Ruby, and 
Smalltalk 
  Can be compiled to Java bytecode 
  Groovy classes are Java classes 
  Groovy can seamlessly use Java classes 
  Java can seamlessly use Groovy classes* 
  Lots of new languages features 
  GPath, GString, internal iterators, closures, Meta‐
Object Protocol (MOP), and many others 

  JDBC is used for communicating with 
databases 
  HSQLDB: default datasource 
  DataSource.groovy  
  Configuration of DataSources for all your 
environments 
  Easy to switch to a different database, even across 
different deployments 


  Domain classes are central to a Grails 
application 
  Located in grails‐app/domain 
  All attributes persistent unless marked in the  
transients property 
  No getters and setters necessary 
  Validators: speciﬁed in constraints property 
  GORM mapping: customized in the mapping 
property 

  Grails Object Relational Mapping 
  Leverages Hibernate 
  Automatically maps domain objects to 
database 
  Provides query and update facilities 
  Finding objects in the persistence store (ﬁndBy… 
methods). 
  Persistence lifecycle methods (save, update, 
delete). 
  Criteria and HQL query facilities. 

  No need to extend a common persistent base 
class 
  Grails injects GORM functionality into objects at 
run‐time. 
  Declare properties for your domain objects  
  The id or version properties are injected 
automatically. 
  All properties are not null/required by default 


  Associations 
  One‐to‐one, one‐to‐many, many‐to‐many 
  Uni‐directional and bi‐directional  
  Owners deﬁned by using belongsTo property 
  Inheritance hierarchies 
  Table‐per‐hierarchy: All classes map to a single 
table 
  Table‐per‐subclass: Each class maps to its own 
table and JOINs are used 

  Retrieving objects 
  get(), getAll(), read()
  Listing objects 
  list(), listOrderBy*() methods 
  order, sort, offset, and max named 
arguments 
  Dynamic ﬁnders (findBy*()) 
  Use property names of the class 
  Support for many expressions in ﬁnder method 

  Built on Hibernate’s Criteria API 
  Groovy builder is used to build up the criteria 
  Hierarchy of method calls and closures for 
building tree‐like structures 
  Each domain class has a createCriteria() 
method 
  Call get, list, scroll, or count on criteria 
  The criteria builder is used to restrict the query 
  Supports associations and projections 

  Support for Hibernate Query Language 
  find(hql), findAll(hql), and 
executeQuery(hql) for queries 
  executeUpdate(hql) for DML‐style 
opera3ons (sets of updates or deletes) 
  Support for positional and named parameters 


  Handles HTTP requests and determines 
rendering responsibility 
  Many objects are available to your controller 
closures 
  log, params, request, response, session, 
servletContext, ﬂash 
  Interceptors on a controller 
  beforeInterceptor and afterInterceptor closures 


File upload/multipart requests 
 
  Automatic binding to domain objects 
  <g:uploadForm />
Binary response writing 
 
  response.outputStream  
  response.contentType
  Overloaded << operator to append content 
Request InputStream reading 
 
  def incomingText =
request.inputStream.text


  Built upon Spring’s validation framework 
  org.springframework.validation package 
  Domain objects have validation baked in 
  save() and validate() methods trigger validation 
  Validation errors populate errors property on 
domain object 
  Errors 
  Interrogate the domain object instance 
  hasErrors() method and errors property 

  Similar to JSPs 
  Utilizes GPath and GStrings and other cool 
Groovy language features 
  Automatic discovery of Grails taglibs 
  Support for templates 
  Small snippets of view code that other views can 
use 
  Useful for AJAX responses 


  Grails ships with a standard set of taglibs 
  Iteration, filtering, switching, logical taglibs 
  HTML markup creation: links, forms, form fields, 
date picker 
  Validation error checking and rendering 
  Paginating views 
  View template rendering (reusable sub‐views) 
  Custom taglibs are easy 
  Groovy class with a TagLib suffix and resides in 
grails‐app/taglib directory 

  Grails uses Prototype library by default   
  Easily changed to another JavaScript provider 
through Grails plugin system 
  Grails taglibs insulate you from the raw 
JavaScript 
  Remote links, remote forms, remote form ﬁelds, 
before and after callbacks, event handling, eﬀects, 
animations 


  Grails has built‐in support for managing 
message bundles, locales 
  Message ﬁles are managed in the grails‐app/
i18n directory 
  Grails taglib can be used to retrieve messages 
from message bundles 
  Supports parameterized messaging 
  Support for special URL mappings to support 
encoding locale information in the URI 

  Allows for centralization of application 
behavior 
  Necessary component in any non‐trivial Grails 
application 
  Transactional by default, set through the 
transactional property 
  Use the expose property to expose a service 
via remoting to other processes 
  Use with various remoting plugins 

  Reﬂection and the Groovy MetaClass  are 
used to scaﬀold CRUD functionality 
  Enable in the controller class… 

class UserController {

def scaffold = User
…
}


  Extension mechanism for integrating third‐
party functionality 
  About 80 or so plugins today and many more 
coming on board 
  AJAX, JavaScript, Flex/Flash, UI widgets 
  Security, Crypto, CAPTCHA, CAS 
  Database migration, code coverage, functional 
testing 
  Many others…ﬁnd at grails.org/plugin/list 

  Swing GUI console 
  Allows execution of arbitrary Groovy 
statements 
  Your Grails domain model is accessible in this 
environment 
  GORM facilities are available 
  Great way to tinker and play with your domain 
object model 


  Eclipse 
  Plugin available, but the story is not good at the 
moment 
  NetBeans 
  Groovy and Grails support in version 6.5 
  IntelliJ IDEA 
  JetGroovy plugin by JetBrains oﬀers good support 
for Grails 
  Seems to be the leader at the moment 

  Take Grails on a test drive! 
  grails.org 
  Books 
  Groovy in Action 
  The Deﬁnitive Guide to Grails, Second Edition 
  Beginning Groovy and Grails 
  Grails in Action 
  Groovy and Grails Recipes 
  Grails Persistence with GORM and GSQL 


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