Groovy and Grails Introduction

1. The Buzz About Groovy and Grails
Presented at
The Chicago Groovy User Group
by Eric Weimer
on March 10, 2009

2. Bio
• Eric B. Weimer
• 26 years developing software
• 10 years with Java stack
• Redpoint Technologies (sponsor)
• Roles
• Developer
• Independent consultant
• Application Architect
• Project/Program Manager
• Director Level
• Approach
• Fun and Agile
• “Life is a banquet”

3. Objectives
This talk is a presentation of my research. It will
answer the following questions:
• What is Groovy?
• What is Grails?
• What do they mean to Java developers?
• What do they mean to IT managers?
• Hidden secrets such as “how do I get first class
plane tickets for the price of coach?”

4. Groovy Defined
Groovy:
• Is a general purpose programming language
• Is a superset of Java syntax
• Fully Object-Orientated (no primitives!)
• Provides many “next generation” features from
Smalltalk, Python, Ruby and others.
• Designed to improve productivity
• Has become wildly popular

5. Grails Defined
Grails:
• Is a web application framework
• Is “full stack”
• Runs on Groovy
• One of many Groovy frameworks available
• Wildly popular
• Leverages Rails‟ Convention over Configuration
• Leverages Closures

6. Putting it all together
Groovy
runs on
Java Object Model
runs on
Java Virtual Machine
6

7. Putting it all together
Groovy
compiles to
Bytecode
runs on
Java Virtual Machine
7

8. Putting it all together
Frameworks
Grails (web Griffon (Swing
applications) applications)
Groovy
8

9. History of computing languages
The first programs looked like this:
0010 1101 0101 1100 0100 1011 0100 1010 1011 1100
0110 1110 0001 0000 0101 0011 0010 1111 0111 0011
0101 0011 0100 1111 0001 1000 0110 0101 1011 1100
0010 1101 0101 1100 0100 1011 0100 1010 0111 0011
0110 1110 0001 0000 0101 0011 0010 1111 1011 1100
0101 0011 0100 1111 0001 1000 0110 0101 0111 0011
0010 1101 0101 1100 0100 1011 0100 1010 1011 1100
0110 1110 0001 0000 0101 0011 0010 1111 0111 0011
0101 0011 0100 1111 0001 1000 0110 0101 1011 1100
0010 1101 0101 1100 0100 1011 0100 1010 0111 0011
0110 1110 0001 0000 0101 0011 0010 1111 1011 1100
0101 0011 0100 1111 0001 1000 0110 0101 0111 0011

10. Historical Documents

11. Early Russian Programmers

12. Programming was quite lucrative

13. How do I install Groovy and Grails
Easy:
• Download and unzip Groovy and Grails
• Set GROOVY_HOME, GRAILS_HOME
• Add %GROOVY_HOME%/bin to Path
• Add %GRAILS_HOME%/bin to Path
Optional:
• Install your IDE‟s Groovy plugin

14. Groovy Buzz Words
• Groovy Truth
• Duck Typing
• Syntactic Sugar
• Fully Object Orientated
• Closures
• Dynamic Objects
• Mixins
• Meta Object Protocol
• And more…

15. Groovy Truth
How Groovy handles boolean comparisons
•Groovy supports the standard conditional operators on
boolean expressions
•In addition, Groovy has special rules for coercing non-
boolean objects to a boolean value.
•Empty collections are false, non-empty are true.
•Empty maps are false, non-empty are true.
•Null object references are false, non-null are true.
•Non-zero numbers are true.

16. Groovy Truth
Examples:
def obj = null;
if ( obj ) …
obj = new Person()
if ( obj ) …
def numSnakes = 0
if ( numSnakes ) …

17. Duck Typing
If it looks like a duck and quacks like a duck, …
def identity = new Identity()
…
identity = new Person()
…
identity = “Eric”

18. Syntactic Sugar
Syntactic Sugar
•An alternative syntax
•More concise
•Improved clarity
•Improves productivity
•Syntactic sugar usually provides no additional
functionality

19. Syntactic Sugar
// Semicolons are only required when necessary:
String friend = „Matt‟
// Parentheses are optional
println “eric has ${numDogs}‟s dogs”
// Except when the compiler cannot tell:
person.save(); children.save()
// return is optional

20. Syntactic Sugar
// Class variables are private by default in Groovy.
// Groovy generates the getters and setters for you:
class Person {
String firstName
String lastName
}
// In Groovy these are the same:
String firstName = p.getLastName( )
String firstName = p.lastName

21. Syntactic Sugar
// Groovy makes great use of the dot operator.
//
// Consider a web page. Groovy supports syntax for navigating
// hierarchical structures with Groovy Builders:
def page = DomBuilder( … )
// Get all the anchors in a page
List anchors = page.html.body.‟**‟.a

22. Syntactic Sugar
// Groovy supports the Java for loop:
for (int i = 0; i < 10; i++) { … }
// However a “sweeter” version of this is
(0..9).each { … }
// Or just
10.times { … }

23. Syntactic Sugar
// constructor sweetness
def person = new Person(
firstName: quot;Ericquot;,
lastName: quot;Weimerquot;,
address: new Address(
addressLine1: quot;101 Main Streetquot;,
city: quot;Lislequot;,
zipCode: quot;60532quot;)
)

24. Syntactic Sugar
//Define an ArrayList:
def petList = [„Rocket‟,‟Portia‟,‟Cleo‟,‟Java‟]
// Define a HashMap
def employeeCellPhoneMap =
[Karl: „847-699-3222‟,
Emelye: „630-605-4355‟,
Natalie: „312-555-1234‟]

25. Fully Object Orientated
// Common Java bug
public boolean sameName (String aName) {
String name = “Matt”;
return name == aName;
}
…
boolean b = sameName(“Matt”);

26. Fully Object Orientated
Java primitives (int, short, long, double, char, etc.)
• In Java, operators only make sense for primitives
• What to do with comparison operators? (==, >, <, ...)
• Answer: Make them work for objects
• Via operator overloading!
• But isn‟t operator overloading a bad thing?
• Not unless it is abused…
• Groovy makes it intuitive

27. Groovy Operators
Groovy Comparison Operators
Operator Method
a == b a.equals(b)
a>b a.compareTo(b) > 0
a >= b a.compareTo(b) >= 0
a<b a.compareTo(b) < 0
a <= b a.compareTo(b) <= 0

28. Groovy Math-like operators
Groovy Math-like operators
Operator Method
a+b a.plus(b)
a-b a.minus(b)
a*b a.multiply(b)
a/b a.divide(b)
a++ or ++a a.next()
a-- or --a a.previous()
a << b a.leftShift(b)
Array Operators
Operator Method
a[b] a.getAt(b)
a[b] = c a.putAt(b, c)

29. Fully Object Orientated
// Groovy version works as expected!
public Boolean sameName (String aName)
{
String name = “Stu”
name == aName
}
…
boolean b = sameName(“Stu”);

30. Closures
• A closure in Groovy is an object
• Java has syntax for strings: String x=“eric”;
• Groovy contains a syntax for closures
• In Groovy, a closure is defined by braces {…}
• As an object, you may assign it to a variable
• As an object, you may pass it to methods
• It can also reference any variables in scope

31. Closures
// A trivial example:
public void printList(List a) {
def pl = {println it}
a.each (pl)
}

32. Closures in Grails
class ItemController {
def save = { …
}
def search = { …
}
def get = {
}
}

33. Dynamic Objects
• You can add methods and properties to classes
or objects.
• You can intercept method calls.
• Many examples such as tracking changes to a
POGO or POJO, logging, business rules, etc.

34. Mixins
Add methods to ANY class at runtime (even Java final).
// Assume you‟ve defined methods wordCount,
charCount:
File.mixin WordCount, CharCount

35. Meta Object Protocol
Metaprogramming
Metaclasses represent the runtime behavior of your
classes and instances. Available per class and per
instance.
ExpandoMetaClass DSL streamlines metaclass use.
Number.metaClass.multiply = { Amount amount ->
amount.times(delegate) }

36. Meta Object Protocol
Metaprogramming
Metaclasses can add properties:
File.metaClass.getWordCount = {
delegate.text.split(/w/).size()
}
new File('myFile.txt').wordCount

37. There is much more to Groovy
• Builders
• DSL
• Swing support (Griffon)
• Template framework
• Groovy Server Pages
• AST transformations
• Grape
• JMX Builder, OSGi support, etc. etc. etc.

38. Grails – what is it?
• Grails is a modern, full stack web application
framework in a box
• Grails is built in Spring and Hibernate
• Grails comes complete with a web server,
database, testing framework, automated build and
logging.
• Grails is not an RoR clone, it is inspired by Rails.
• Best demoed by example.

39. Grails – what is it?
• A full stack web framework built on Groovy
• Leverages proven industry standards like Spring
and Hibernate
• Supports “Convention over configuration” like Rails
• Makes use of closures like Rails
• Not designed to be a Groovy-based Rails, but
designed to be better than Rails

40. Groovy Myths
• Groovy is a scripting language
• Sun favors JRuby over Groovy
• Groovy is slow and full of bugs
• Java is sufficient for our needs
• Now that SpringSource has acquired Groovy,
and now that Spring favors paying customers,
does that mean Groovy is destined to be closed
source and require a fee?

41. Barriers to entry
Approval to use a new language can be difficult.
• Some shops require an elaborate process to
approve a new language.
• Hint: Begin with Groovy for unit testing
• Hint: Use Groovy for Ant scripting
• Present results of polls, statistics, etc. to show
Groovy has a large community of support
• Create a compelling argument for Groovy
adoption
• Emphasize productivity gains, competitive
advantage

42. In conclusion
How compelling are Groovy and Grails?
• Production ready
• Improves developer productivity
• Reduces bugs
• Eases migration for legacy Java developers
• Excellent documentation
• Community is growing geometrically
• Mainstream community awareness through
SpringSource
• Widespread anecdotal evidence of the claims above
• Lacks published metrics to support claims above

43. Recommended Reading
For beginners without Rails or Django experience:
Beginning Groovy and Grails: From Novice to Professional (Beginning from Novice to
Professional) by Christopher M. Judd, Joseph Faisal Nusairat, and Jim Shingler
Groovy and Grails Recipes (Recipes: a Problem-Solution Approach) by Bashar Abdul-Jawad
For the experienced:
Groovy in Action by Dierk Koenig, Andrew Glover, Paul King, and Guillaume Laforge
Programming Groovy: Dynamic Productivity for the Java Developer (Pragmatic
Programmers) by Venkat Subramaniam
Groovy Recipes: Greasing the Wheels of Java (Pragmatic Programmers) by Scott Davis
The Definitive Guide to Grails, Second Edition (Expert's Voice in Web Development) by
Graeme Rocher and Jeff Brown

44. In conclusion
You can find these slides on my blog at:
ericbweimer.blogspot.com
Thanks for coming!
Don‟t forget to stay for the prizes donated by Redpoint.