Slides from a workshop about Grails.

1. Introduction to
Łukasz Tenerowicz
lukasz.tenerowicz@gmail.com
lukasz.tenerowicz@itsilesia.com

2. Disadvantages of web apps in Java ?
● Hard configuration (e.g. XML soup )
● Large amounts of boilerplate code ( vs.
scripting languages like PHP, Python)
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3. Grails = No disadvantages of Java
● Convention over configuration - like in
RoR
● Groovy as a primary language
○ Short syntax
○ Easy!
○ Functional elements
● Configuration also in Groovy
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4. … + its advantages
● Lots of libraries
○ Spring ( DI, Transactions, Spring Security )
○ Hibernate
○ Quartz
○ Lots of APIs ( e.g. Amazon Web Services Java
SDK)
● Deployment via .war file
● ~20 years of JVM development
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5. About Grails
● version 1.0 in 2008
● Looks similar to Ruby on Rails
○ MVC
○ convention over configuration
○ console
● Based on Spring MVC, Hibernate
● Used in LinkedIn, Netflix, Sky TV,
Vodafone
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6. Folder structure source : https://grails.org/Quick+Start
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7. Our first task will be ...

8. Hello World!
What else ? :D

9. Controller
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● Class name and
method name maps to
an URL
○ /hello/index
○ /hello/show

10. Controller - parameters
● URL parameters are mapped to method
arguments
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● Also accessible
from params map

11. Hello world!
● render(“Hello world”)
● render(“Hello “ + user)
● Views! ${user}
● render(view: ‘index’, model: [user: ‘user’])
● return [user: ‘user’]
● redirect(action: ‘index’)
● GSP -> g:if, g:each
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12. But that’s all static HTML...
Give me the DB!

13. Domain classes
What our application is all about

14. Domain classes
● Mapped to database via GORM
○ Class is table, property is column
● Constraints
○ nullable, unique, blank, size, ...
● Relations
○ hasMany, belongsTo
● Properties
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15. Domain classes - constraints
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16. Domain classes - relationships
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17. Domain classes - properties
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18. Domain class: finders and other functions
● Person.findByName(‘asdf’)
○ Person.findByNameAndAge(‘asdf’, 16)
○ Person.findAllBy...And…
● Person.save()
○ Person.discard()
○ Person.refresh()
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19. Data binding
Powerful!!!

20. Databinding of a domain class
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21. Validation
● Domains and all classes with
@Validateable
● Occurs on obj.validate() or during
databinding
● If any constraints are violated, error
codes are added to obj.errors map
● Those errors can be rendered via i18n
codes
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22. Internationalisation - i18n
● Based on codes found in /grails-app/
i18n/messages.properties
● Tags : <g:message code=”com.some.code” />
● So yes, we can render errors too!
○ <g:message error=”${object.errors}” />
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23. Dependency
Injection
Easier than ever!

24. Other features
Maybe next workshops :P

25. Other features
● REST controllers - http://grails.
org/doc/latest/guide/webServices.html
● Spring Security - http://grails.org/plugin/spring-security-core
● Database migrations - http://grails.org/plugin/database-migration
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26. Thank you!
Questions ?