Grails: Spring+Hibernate development re-invented Grails = Groovy + Spring + Hibernate

Power and simplicity Productivity and pleasure at last!

By Guillaume Laforge

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About me

Guillaume Laforge

Groovy Project Manager at Codehaus JSR-241 Spec Lead Initiator of the Grails Web framework

Co-author of « Groovy in Action » – Manning

Software Architect at OCTO Technology• A French-based consulting company focusing on

Software Architecture and Agile Methodologies

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Goal of this talk

Learn how to leverage the Groovy web framework Grails to improve developer productivity and code clarity

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Agenda

The pains of web development with Java frameworks What’s Grails? MVC through the pain point prism

Model: transparent Hibernate persistence View: GSP, SiteMesh layouts, dynamic taglibs Controller And Services, Jobs, Ajax…

Sweet spot: Enterprise-readiness Further reading

The pains of web development with Java frameworks

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Has it got to be that complex?

Seriously, web development is often painful!

The pain points: ORM persistence overly hard to master and get right Numerous layers and configuration files lead to chaos Ugly JSPs with scriptlets and the complexity of JSP tags

Grails addresses the fundamental flaws in Java web application development today without compromising the platform

What’s Grails?

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Grails principles

Grails is an MVC action-based web framework

Principles CoC: Convention over Configuration DRY: Don’t Repeat Yourself

Grails has the essence of frameworks like Ruby on Rails Django, TurboGears

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Grails foundations Grails is built upon solid bricks &

best of breed components

Spring: IoC, DI, Spring MVC, transaction support, etc… Hibernate: ORM, querying mechanism Groovy: for focusing on everything that matters SiteMesh: page layout and composition AJAX libraries: for Web 2.0 user interactivity

Pain point one ORM persistence overly hard to master and get right ibatis.xml

hibernate.cfg.xml

persistence.xml

ejb-cmp.xml

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GORM Grails Object Relational Mapping

The domain model is just a set of POGOs(Plain Old Groovy Object)

POGOs are automatically and transparently mapped to the DB on application startup

No more hibernate.cfg.xml!

Grails provides sensible defaults

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Let’s model a small domain

class Book { String title Author author Publisher publisher

def belongsTo = [Publisher, Author]

String toString(){ title }}

class Author { String firstName String lastName

def hasMany = [books: Book] String toString(){ "$firstName $lastName" }}

class Publisher { String name

def hasMany = [books: Book] String toString(){ name }}

Author has many Books Publisher has many Books

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Scaffolding to the rescue

Scaffolding is the art of generating parts of the application to get started quickly

Grails scaffolds controllers and views

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Constraints validationAdd an email to Author

class Author { String email static constraints = { email(email: true)} }

Add an ISBN to Book

class Book { String isbn static constraints = { isbn(matches: "[0-9]{9}[0-9X]")} }

Many constraints available blank, creditcard, email, inList, length, matches, max,

min, nullable, range, size, unique, url, validator

Custom validator even ( validator: { it % 2 == 0 } )

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Querying your model (1/3)

Forget about the boring DAO pattern!

Grails provides various querying mechanisms: Dynamic finder methods Query by example Criteria builders Full-blown HQL queries

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Querying your model (2/3)

Dynamic finder methods Book.findByTitle("The Stand")

Book.findByTitleLike("Harry Pot%") Book.findByReleaseDateBetween(start, end) Book.findByTitleLikeOrReleaseDateLessThan( "%Grails%", someDate)

Find by relationship Book.findAllByAuthor( Author.get(1) )

Affect sorting Book.findAllByAuthor( me, [sort: ‘title’, order: ‘asc’] )

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Querying your model (3/3)

Query by example Book.find ( new Book(title: ‘The Shining’) )

HQL queries Book.find(" from Book b where b.title like ‘Lord of%’ ") Book.find(" from Book b where b.title like ? ", [‘Lord of%’])

Criteria builder def results = Account.createCriteria() {

like("holderFirstName", "Fred%") and { between("balance", 500, 1000) eq("branch", "London") } order("holderLastName", "desc") }.list()

Pain point two Numerous layers and configuration files chaos

web.xmlxwork.xml

applicationContext.xml

sitemesh.xml

struts-config.xml

validator.xml

faces-config.xml

tiles.xml

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A sample controllerclass BookController { def index = { redirect(action:list,params:params) }

def list = { [ bookList: Book.list( params ) ] }

def show = { [ book : Book.get( params.id ) ] }

def edit = { def book = Book.get( params.id ) if(!book) { flash.message = "Book ${params.id} not found" redirect(action:list) } else return [ book : book ] }}

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Conventions and handy dynamic

methods URL mapping convention: controller/action/idhttp://localhost:8080/library/book/show/1

Scaffolding can be dynamic (def scaffold = true) static (code generation)

Controllers pass data to the view through simple maps Direct access to parameters Easy redirect and forward with dynamic methods Can define allowed HTTP methods for each action

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Services injected in your controllers

Services are Groovy classes that should contain your business logic

Automatic injection of services in controllers & services simply by declaring a field:

class BookController { MySuperService mySuperService}

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Job scheduling

You can create recuring events with Quartz under the hood, configured by Spring

Again a convention on name and directory Regular intervals, or cron definitions

class MyJob { def cronExpression = "0 0 24 * * ?" def execute() { print "Job run!" }}

Pain point three Ugly JSPs with scriptlets and the complexity of JSP tags

c.tld

fmt.tld

spring.tld

grails.tld

struts.tld

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Views Spring MVC under the hood Support for flash scope between requests GSP: Groovy alternative to JSP Dynamic taglib development:

no TLD, no configuration, just conventions Adaptive AJAX tags (Yahoo, Dojo, Prototype) Customisable layout with SiteMesh Page fragments through reusable templates Views under grails-app/views

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GSP: Groovy Server Pages

<html> <head> <meta name="layout" content="main" /> <title>Book List</title> </head> <body> <a href="${createLinkTo(dir:'')}">Home</a> <g:link action="create">New Book</g:link> <g:if test="${flash.message}"> ${flash.message} </g:if> <g:each in="${bookList}">${it.title}</g:each> </body></html>

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Rich set of dynamic taglibs

Logical: if, else, elseif Iterative: while, each, collect, findAll… Linking: link, createLink, createLinkTo Ajax: remoteFunction, remoteLink, formRemote,

submitToRemote… Form: form, select, currencySelect, localeSelect,

datePicker, checkBox… Rendering: render*, layout*, paginate… Validation: eachError, hasError, message UI: richTextEditor…

Many external contributions for new taglibs!

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Write your own taglib and reload it!

Yet another Grails convention:

class MyTagLib { def isAdmin = { attrs, body -> def user = attrs['user'] if(user != null && checkUserPrivs(user)) body() }}

Use it in your GSP:

<g:isAdmin user="${myUser}"> some restricted content</g:isAdmin>

Sweet spot: Enterprise-readiness

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Protect your investment

Reuse Existing Java libraries Employee skills & knowledge Spring configured beans Hibernate mappings for legacy schemas

(but still benefit from dynamic finders) EJB3 annotated mapped beans JSPs, taglibs for the view

Deploy on your pricey Java app-server & database

Grails will fit in your JEE enterprise architecture!

Further reading Groovy and Grails books Resources on the Web Grails eXchange 2007 conference Groovy London User Group

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Groovy and Grails books to go further

Groovy in Action Manning

The Definitive Guide to Grails Apress

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Groovy and Grails on the Web

Grails eXchange 2007 conference in London http://www.grails-exchange.com

Grails web framework http://grails.org

Groovy dynamic language for the JVM http://groovy.codehaus.org

AboutGroovy news site on Groovy & Grails http://aboutgroovy.com

Getting started with Grails InfoQ book http://www.infoq.com/minibooks/grails

GroovyBlogs javablogs-like agregator built with Grails http://groovyblogs.com

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Grails eXchane conference

Don’t miss the Grails eXchange 2007 conference! 4 tracks

The Groovy Language The Grails framework Ajax and Web 2.0 Java Enterprise Edition

Famous speakers from Interface21, Google, JBoss, Sun Tonight: London Groovy & Grails User Group meeting

18:30 at SkillsMatter HQ

Summary

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Summary and beyond! Grails

Lowers the barrier of entry onto the Java platform Brings back both productivity and pleasure of development Lets you build applications in an incremental way Allows you to scale your app in complexity and infrastructure

Only scratched the surface! We haven’t mentionned: Everything can be unit-tested easily, Canoo Web Test integration Flexible plugin architecture to create new artifacts Spring bean builder to script Spring configs Scripting environment (consoles to test your code manually) How we can reuse Java libraries, external mappings, spring confs

Questions and Answers