Grails 101

Grails
High-velocity development for Spring applications

About Me
David Jacobs
● Web Developer since '98

● Groovy since '06 Twitter
@MetaThis
● Grails focus in '08-'09

What is Grails?
Grails is an open-source framework for high-velocity
development of Spring applications
● Sensible defaults
● Convention-over-configuration
● DRY
● Dynamic metaprogramming
● End-to-end integrated stack
● Enables you to focus on the business problem

Best-of-Breed Java Technologies
● Spring
● Spring MVC
● Hibernate
● log4j
● jUnit
● SiteMesh

Integrated Stack
● Layers and technologies integrated and wired
out-of-the-box
● Default configurations based on industry best
practices
● 80/20 rule

Directory Structure
● grails-app - top level directory for Groovy sources
● conf - Configuration sources.
● controller - Web controllers - The C in MVC.
● domain - The application domain.
● i18n - Support for internationalization (i18n).
● services - The service layer.
● taglib - Tag libraries.
● views - Groovy Server Pages.
● scripts - Gant/Gradle scripts.
● src - Supporting sources
● groovy - Other Groovy sources
● java - Other Java sources
● test - Unit and integration test

GORM
● Object Relational Mapping (ORM)
● Data access layer
● Simplifies configuration through conventions
● Defaults to Hibernate implementation
● Provided as plugin, alternatives pluggable
● Extends and simplifies data access APIs
● Similar to ActiveRecord in Rails

GORM
Domain Modeling
//this is a complete Hibernate mapping!
class Employee {
String firstName
String lastName
Date startDate
}

GORM
Dynamic CRUD
def employee = Employee.get(1)
employee.delete()
def newEmployee = new Employee(firstName: “Joe”, lastName: ”Programmer”)
newEmployee.save()

GORM
Dynamic finders
Employee.findByLastNameAndHireDateGreaterThan(“Jones”, someDate)

findBy and findAllBy
● InList - In the list of given values
● LessThan - less than the given value
● LessThanEquals - less than or equal a give value
● GreaterThan - greater than a given value
● GreaterThanEquals - greater than or equal a given value
● Like - Equivalent to a SQL like expression
● Ilike - Similar to a Like, except case insensitive
● NotEqual - Negates equality
● Between - Between two values (requires two arguments)
● IsNotNull - Not a null value (doesn't require an argument)
● IsNull - Is a null value (doesn't require an argument)

GORM
Hibernate HQL
Employee.findAll("from Employee as e where e.lastName like :lastName", [lastName:"Jon%"])

//with pagination and sorting
Employee.findAll("from Employee as e where e.lastName like :lastName",
[lastName:"Jon%", max:10, offset:20, sort:"hireDate", order:"asc"])

GORM
Simplified Hibernate Criteria API
// Find incomplete tasks assigned to Jones where the company is Monsanto
// and the project name begins with “Rubic”, order by task name
def criteria = Tasks.createCriteria()
def tasks = criteria.list {
eq(‘completed’, false)
project{
like(‘name’ ‘Rubic%’)
company{
eq(‘name’, ‘Monsanto’)
}
assignedEmployees{
eq(‘lastName’, ‘Jones’)
}
}
order(‘taskName’, ‘asc’)
}

Web Layer
● Controllers built on Spring MVC
● URL mapping conventions map requests to controllers
● Naming and directory conventions map actions to views
● Built-in AOP action interceptors
● Every controller provides a beforeInterceptor and afterInterceptor
● Specifiable by action, optionally with patterns and exclusions
● Servlet objects and convenience extensions injected into controller actions at runtime and
provided as implicit variables
● servletContext, session, request, response, params, flash

Spring MVC
Request parameters parsed into multidimensional params map
● Easily accessed with powerful Groovy map support.

<input type=”text” name=”userName” />
//controller code
def userName = params.userName

<input type=”text” name=”user.address.zipCode” />
<input type=”text” name=”user.address.state” />
//controller code
def zipCode = params.user.address.zipCode
def state = params.user.address.state

Data Binding
def save = {
//bind params to new instance
def user = new User(params)

//persist
user.save()
}

def update = {
//get instance from database
def user = User.get(params.id)
//bind params
user.properties = params
user.save()
}

Request Format Transparency
Grails codecs (dynamic encode/decode methods) easily automap formats like XML and JSON to
the params map.

<user>
<id>42</id>
<address>
<zipCode>63122</zipCode>
</address>
</user>

//transparent to the controller code
def zipCode = params.user.address.zipCode
def user = new User(params.user)

Easily create custom codecs to support specific requirements

XML & JSON Marshalling
Groovy's popular XML support
+
Grails builders and codecs
+
Convenience methods

def list = {
render Project.list() as XML
}

def list = {
render Project.list() as JSON
}

Groovy Server Pages (GSP)
● Similar to JSP
● Tag library like JSTL, but much more powerful
● Easy custom tags
● Powerful templates
● SiteMesh is automatically configured for layout management

Groovy Server Pages (GSP)
Tags
actionSubmit fieldValue layoutBody render
applyLayout findAll layoutHead renderErrors
checkBox form layoutTitle resource
collect formRemote link select
cookie formatBoolean localeSelect set
country formatDate message sortableColumn
countrySelect formatNumber meta submitButton
createLink grep pageProperty submitToRemote
createLinkTo hasErrors paginate textArea
currencySelect header passwordField textField
datePicker hiddenField radio timeZoneSelect
each if radioGroup unless
eachError include remoteField uploadForm
else javascript remoteFunction while
elseif join remoteLink

AJAX
● Bundled with Prototype and Script.aculo.us
● Excellent jQuery plugin
● GSP tags for AJAX
● Adapters built-in for major JavaScript frameworks
● Plugins provide additional AJAX functionality

Configuration
Per-Environment Configuration Supports SCM
● Package or run as any configured environment. Default environments and build configurations defined for
development, test (staging) and production.
● Programmatic environment detection with provided Environment class.

environments {
development {
dataSource {
dbCreate = "create-drop" // one of 'create', 'create-drop','update'
url = "jdbc:hsqldb:mem:devDB"
}
}
test {
dataSource {
dbCreate = "update"
url = "jdbc:hsqldb:mem:testDb"
}
}
production {
dataSource {
dbCreate = "update"
url = "jdbc:hsqldb:file:prodDb;shutdown=true"
}
}
}

Plugins
Grails extensions are provided as plugins
● Created by core Grails team and community
● Powerful – a plugin IS a Grails application
● Plugins typically bring the idioms of convention-over-configuration and simplified APIs to
popular libraries
● Easy to create your own – provides a strong architecture for re-use across projects
● Examples
● Spring Security
● JMS
● Spring WS
● LDAP
● Quartz

Plugins
Plugin development is very active

The Bottom Line
● Increases developer productivity
● less code + less configuration = easier to maintain
● Smaller learning curve than other Java web frameworks
● Eases the learning curve for the underlying technologies
● Project layout conventions and a standard technology stack promote quicker ramp-up time from one
Grails project to another
● Increases agility potential through rapid proto-typing and quick customer feedback
● Guides solid technology choices by providing excellent defaults
● Developers enjoy it, which promotes morale and retention

Grails 101

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