(A case for) GRAILS

Mark DaughertyCITYTECH, Inc.July 7th, 2010

Outline

• Inspiration• Grails overview• Comparison of Java/Spring/JPA application to

Groovy/Grails

Context

• February 2010 : wrote a small Groovy/Grails app to learn the technologies

• March 1st, 2010 : started on CDGA project (Struts, Spring, JPA)

• March 1st, 2010 (later that day) : realized that CDGA had an enormous amount of boilerplate code that Grails could eliminate

(Additional) Context

• May 7th, 2010 : wrote CITYTECH blog post about code savings from replacing Spring DAO code with Grails

• May 8th, 2010 – present : blog is read by a total of 4 CITYTECH employees

• July 7th, 2010 : Grails begins to learn at a geometric rate. It becomes self-aware at 2:14 AM, Eastern time.

Grails Primer

• Web application framework built with Groovy (Java-based dynamic language) on top of proven Java technologies– Spring MVC, Hibernate

• Full stack for rapid development– Embedded Tomcat container, HSQLDB, (G)Ant,

scaffolding features– Get a basic app running within minutes

You may notice…

• Convention over configuration– Little-to-no initial configuration– Project structure is predefined according to best

practices– Command line scripts for common tasks• Create new application, compile, test, run• Generate domain classes, controllers, services, test

cases• Install plugins

– Contrast with your last Maven-built project

In practice…

Simple Domain

Delegate 1 ∞ UserDelegate 1 ∞ Application

A “delegate agency” has one-to-many users and one-to-many applications. An application contains various forms, input by users, to collect data about the delegate agency.

JPA (Java Persistence API)@Entity@Table(name = "USER")public class User implements Serializable {

@Id private Integer id;

@OneToOne(fetch = FetchType.LAZY) @JoinColumn(name = "DELEGATE", referencedColumnName = "ID") private Delegate delegate;

// getters and setters, equals(), hashCode(), toString()…}

(More) JPA@Entity@Table(name = "DELEGATE")public class Delegate implements Serializable {

@Id private Integer id;

@OneToMany(cascade = { CascadeType.ALL }, fetch = FetchType.EAGER) private Set<User> users;

@OneToMany(cascade = { CascadeType.REMOVE }, fetch = FetchType.LAZY) private Set<Application> applications;

// getters and setters, equals(), hashCode(), toString()...}

(Still more) JPA@Entity@Table(name = "APPLICATION")public class Application implements Serializable {

@Id private Integer id;

@ManyToOne(cascade = { CascadeType.REFRESH }, optional = false) @JoinColumn(name = "DELEGATE”) private Delegate delegate;

// getters and setters, equals(), hashCode(), toString()...}

Grailsclass User {

static belongsTo = [delegate:Delegate]}

class Delegate {static hasMany = [users:User, applications:Application]static mapping = { users lazy:false

applications cascade:'delete'}

}

class Application {static belongsTo = [delegate:Delegate]static mapping = {

delegate cascade:'refresh'}

}

DAO

• JPA/Hibernate = verbose, repetitive– Even a small domain model can have 1000’s of

lines of code for basic CRUD operations– Tedious to maintain

GORM!

• Hibernate under the hood• Groovy + runtime code synthesis to eliminate

boilerplate code

Basic CRUD

Dynamic Finders

Additional GORM Features

• ORM DSL for mapping to legacy DB schemas– Custom mappings for non-standard table and

column names• Event handlers (beforeInsert, afterUpdate)• Customizable caching and fetching strategies,

transactions

Web

• Render XML or JSON responses using markup builders– Automatic marshalling of domain classes to

XML/JSON

(More) Web

• GSP– Similar to JSP, but with better tag libraries• findAll, grep (filter) for collections• Method calls

• Templates• Sitemesh (decorator) layouts• Customizable URL mappings

Validation

• Often painful, less so with Grails

More Features

• Spring Web Flow– Supports subflows, conversation scope (similar to

Seam)• Interceptors / Filters• AJAX– DOJO, GWT plugins

Even more to like

• Groovy tests– Ideal for TDD– Unit tests created automatically from command line script– Dynamic language features for easy mocking

• Easy RESTful web services– URL mappings– Controllers can render XML or JSON– Consider attending a CGUG meeting

• Extremely active community– 400+ plugins (Spring Security, JQuery, GWT, Google App Engine, Flex)– Wide range of tutorials– Frequent releases

Summary

• Grails compared to Spring, EJB, JPA– Substantially less code without compromises– Easier to maintain and test– Shorter iterations and release cycles– Same proven underlying technologies– Gain competitive edge

• Why not?