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Introduction to Grails by Jason McDonald Java Users Group Charleston, SC June 25, 2008 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 http://www.grails.org 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 ${…} Tag Libraries • Ordering and sorting <g:sortableColumn property="releaseDate" defaultOrder="desc" title="Release Date" titleKey="book.releaseDate" /> • Form display <g:form name="myForm" action="myaction" id="1"> <g:passwordField name="myPasswordField“ value="${myPassword}" /> ... </g:form> • Formatting <g:formatDate format="yyyy-MM-dd" date="${date}"/> Custom Tag Libraries • • • Custom tag libraries are just groovy classes that end with TagLib Defaults to ‘g’ namespaces unless declared Closure defines actual tag: class FormattingTagLib { static namespace = ‘fmt’ def dateFormat = { attrs -> out << new java.text.SimpleDateFormat( ‘dd-MM-yyyy’).format(attrs.date) } } <fmt:dateFormat date=‘${plan.effDate}’ /> 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’]) 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