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

Getting Started

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

Underlying Technologies Spring Hibernate Log4J Junit Quartz Ant

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

Installation Visit Download and extract files Create GRAILS_HOME environment variable Add %GRAILS_HOME% to PATH environment variable That’s it!

Grails Structure

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

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

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]

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

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

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"] } }

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

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)

Grails MVC

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

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

Tag Libraries Ordering and sorting Form display... Formatting

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

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

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

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

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’ }

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

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

Grails in Action

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 service: static expose = [‘xfire’]

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

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

The Example

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)

Open Discussion