Java Users Group

1
Java Users Group
Introduction to Grails
by Jason McDonald

• 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
• 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
• Thats 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
• 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
  herestatic mappings "/product/id?"(contro
  ller"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 sortingltgsortableColumn
  property"releaseDate"
  defaultOrder"desc" title"Release
  Date" titleKey"book.releaseDate" /gt
• Form displayltgform name"myForm"
  action"myaction" id"1"gt ltgpasswordField
  name"myPasswordField value"myPassword"
  /gt ...lt/gformgt
• FormattingltgformatDate format"yyyy-MM-dd"
  date"date"/gt

20
Custom Tag Libraries

• Custom tag libraries are just groovy classes that
  end with TagLib
• Defaults to g namespaces unless declared
• Closure defines actual tagclass
  FormattingTagLib static namespace fmt
  def dateFormat attrs -gt out ltlt new
  java.text.SimpleDateFormat( dd-MM-yyyy).forma
  t(attrs.date) ltfmtdateFormat
  dateplan.effDate /gt

21
Internationalization Support

• Based on Java i18n specifications
• Define properties files with language specific
  entries
• Views can read i18n entries with a
  tagltgmessage codemy.message argsOne,
  Two/gt
• Tag libraries can read entries with
  codeg.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 withinstatic
  constraints date(nullable false)
• Can define custom messages using convention
• className.propertyName.constraint Err msg
• Automatic parameter mapping from
  viewbook.properties params

23
GORM

• Grails Object Relational Mapping
• Uses Hibernate3
• Dynamic methods for findingBook.findByTitle(The
  Dark Tower)Book.findByTitleAndAuthor(The Dark
  Tower, Stephen KingBook.findByTitle(Christine
  , sort edition, order asc )
• Relational mapping defined within
• One to manystatic hasMany
  attendancesAttendance
• One to oneAttendance attendance

24
GORM Caching

• Provides the same caching mechanisms that can be
  found with Hibernate3
• Updates to DataSource.groovy can toggle
  cachinghibernate cache.use_second_level_c
  ache 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 alloweddef
  allowedMethods save'POST', update'POST'
• GET is the default
• Auto scaffolding sets up CRUD without filesdef
  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
• Provide RESTful mappings in UrlMappings.groovy
• Implement controller to accept and return
  marshalled data
• SOAP
• Supported through XFire plug-in
• Simply expose a servicestatic expose xfire

29
Testing

• Test framework based on JUnit
• Unit 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
  linegrails dev Dserver.port9999 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