1. Introduction to Grails
by Jason McDonald
Java Users Group
Charleston, SC
June 25, 2008

2. Getting Started

3. Grails Basics Open Source Fully integrated with Java Groovy based
Uses ANTLR to compile Groovy down to JVM compatible bytecode
Predicated on DRY principle

4. Underlying Technologies
Spring
Hibernate
Log4J
Junit
Quartz
Ant

5. Native Support HSQL MySQL Servlet container servers AJAX and DHTML
Jetty
Tomcat
AJAX and DHTML
Dojo
Prototype
Yahoo!

6. Installation Visit http://www.grails.org Download and extract files
Create GRAILS_HOME environment variable
Add %GRAILS_HOME% to PATH environment variable
That’s it!

7. Grails Structure

8. Goovy Roots Built on top of Java Very similar syntax to java
Supports closures
Method returns can be slightly different
Case sensitive
No semi-colons needed
All classes end in .groovy

9. Conditional Environments
Environment conditionals allow for variations for a specific environment
Database
Initialization options
More
Three environment choices
Development
Testing
Production

10. Script Based Code Generation
grails create-app [app name]
grails create-controller [controller name]
grails create-domain-class [class name]
grails create-service [service name]
grails create-unit-test [test name]
grails create-tag-lib [taglib name]
grails generate-all [class name]
grails generate-views [class name]

11. Building, Deploying, and Managing
grails clean
grails compile
grails console
grails doc
grails install-plugin
grails run-app
grails war

12. Important Files conf/DataSource.groovy conf/UrlMapping.groovy
Database connections
conf/UrlMapping.groovy
Routing
conf/BootStrap.groovy
Bootstrap file
conf/Config.groovy
Configurations (MIME mappings, more…)

13. Routing Route rules found in conf/UrlMapping.groovy Default route:
application/controller/action/id[?params]
Additional rules and restrictions can be applied here static mappings = { "/product/$id?"(controller:"product"){ action = [GET:"show", PUT:"update", DELETE:"delete", POST:"save"] } }

14. Databases db configuration is in conf/DataSource.groovy
Can define at environment level or global level
Defaults to HSQL
Change to MySQL by:
Dropping MySQL connector in the lib
Changing DataSource.groovy to point at MySQL

15. Database Create Scheme
dbCreate
create-drop: creates tables on startup and drops them on shutdown (DEV)
create: creates tables on startup, deletes data on shutdown (DEV, TEST)
update – creates tables on startup, saves data between restarts (TEST, PROD)

16. Grails MVC

17. MVC Framework Standard MVC implementation Sits on top of Spring MVC
Reduces repetition of XML developers must maintain
Gives access to Spring DSL

18. Views Groovy Server Pages GSP extension Based on JSP pages Use
Tag libraries
Expressions
similar to JSP EL but allows any expression within ${…}

19. Tag Libraries
Ordering and sorting <g:sortableColumn property="releaseDate" defaultOrder="desc" title="Release Date" titleKey="book.releaseDate" />
Form display <g:form name="myForm" action="myaction" id="1"> <g:passwordField name="myPasswordField“ value="${myPassword}" /> ... </g:form>
Formatting <g:formatDate format="yyyy-MM-dd" date="${date}"/>

20. Custom Tag Libraries
Custom tag libraries are just groovy classes that end with TagLib
Defaults to ‘g’ namespaces unless declared
Closure defines actual tag: class FormattingTagLib { static namespace = ‘fmt’ def dateFormat = { attrs -> out << new java.text.SimpleDateFormat( ‘dd-MM-yyyy’).format(attrs.date) } } <fmt:dateFormat date=‘${plan.effDate}’ />

21. Internationalization Support
Based on Java i18n specifications
Define properties files with language specific entries
Views can read i18n entries with a tag: <g:message code=‘my.message’ args=‘${[‘One’, ‘Two’]}’/>
Tag libraries can read entries with code: g.message(code: ‘my.message’, args: [‘One’, ‘Two’])

22. Models POGOs Fields default to private
Getters and setters provided automatically
Must use wrapper objects – no primitives (1.5?)
Field validation defined within: static constraints = { date(nullable: false) }
Can define custom messages using convention:
className.propertyName.constraint = ‘’Err msg’’
Automatic parameter mapping from view book.properties = params

23. GORM Grails Object Relational Mapping Uses Hibernate3
Dynamic methods for finding Book.findByTitle(“The Dark Tower“) Book.findByTitleAndAuthor(“The Dark Tower”, “Stephen King” Book.findByTitle(“Christine”, [sort: ‘edition’, order: ‘asc’] )
Relational mapping defined within
One to many: static hasMany = [ attendances:Attendance ]
One to one: Attendance attendance

24. GORM Caching
Provides the same caching mechanisms that can be found with Hibernate3
Updates to DataSource.groovy can toggle caching: hibernate { cache.use_second_level_cache = true cache.use_query_cache = true cache.provider_class = ‘org.hibernate.cache.EhCacheProvider’ }

25. Controllers House actions (methods) that respond to a request
Actions should map to GSP of same name
index is the default action
Can define the method each action is allowed: def allowedMethods = [save:'POST', update:'POST']
GET is the default
Auto scaffolding sets up CRUD without files def scaffold = true // In Controller class

26. Action Responses All actions respond in one of three ways: redirect
Equivalent ot response.sendRedirect
Can specify actions, controller, params, and more
return
Returns a value and calls a GSP of the same name (action method ‘go’ will forward to go.gsp)
render
Calls a GSP by name
Has the ability to pass arguments

27. Grails in Action

28. Web Services REST SOAP Provide RESTful mappings in UrlMappings.groovy
Implement controller to accept and return marshalled data
SOAP
Supported through XFire plug-in
Simply expose a service: static expose = [‘xfire’]

29. Testing Test framework based on JUnit Unit tests Integration tests
By convention uses mock objects
Integration tests
By convention use real objects
Functional tests
Supports Canoo WebTest integration

30. Running the Application
Bootstrapping data
Allows for initialization and test data
Jetty Server
Specify port and environment on command line grails dev –Dserver.port=9999 run-app
Tomcat
As war
Exploded

31. The Example

32. Requirements Application needs to:
Store meetings, people, and which meetings each person attends
People should store first and last name
Meetings should store date and subject of meeting
Must have full CRUD capability
Must be web based
Must be able to integrate with Java environments (to meet future integration needs)

33. Open Discussion