1.
Learning Groovy (in 3 hours)!
Adam L. Davis
The Solution Design Group, Inc.
Author of “Learning Groovy”
(& What’s New in Java 8 & others)
14 years Java Dev.
github.com/adamldavis
/2017-gr8conf-learning-groovy

2.
Java ~ Brian Goetz (Java Language Architect)

3.
Groovy

4.
<Insert your
hated language
here>
PHP

5.
groovy-lang.org
sdkman.io

6.
● Dynamic or Static
● (@CompileStatic @TypeChecked)
● As fast as Java (with static & indy)
● Meta-programming
● Optional semi-colons
● Optional parentheses
● Short-hand for Lists and Maps
● Automatic getters and setters
● A better switch
● Groovy GDK…
Groovy 2.4 Features

7.
● Closures
● Currying
● Method references
● Map/Filter/Reduce as collect, findAll, inject
● Internal iterating using each
● Operator Overloading (+ - * % / …)
● methodMissing and propertyMissing
● AST Transformations
● Traits
…
Groovy 2.4 Features (cont.)

8.
Starting Out
Option 1: Using sdkman.io
– sdk install groovy 2.4.9
Option 2: Download from groovy-lang.org
– Alter your PATH
● Export PATH=$PATH:/usr/lib/groovy/bin
● Option 3: Mac – see http://groovy-lang.org/install.html
● Option π: Windows – see https://github.com/groovy/groovy-windows-installer
Then: $ groovyConsole
IntelliJ IDEA or NetBeans

9.
Dynamic typing
● def keyword
● Parameters’ typing optional
● Possible to mock using a map
– def dog = [bark: { println ‘woof’ }]
● Using @TypeChecked or @CompileStatic you
can make Groovy statically typed in some
classes

10.
Groovy Strings
● ‘normal string’
● “groovy string can contain $variables”
● “can also do expressions ${x + 1}”
● Use triple quote to start/end multi-line strings
‘’’
This is a
Multi-line
String
‘’’

11.
Math, Groovy Truth, and Equals
● Numbers are BigDecimal by default not Double
– 3.14 is a BigDecimal
– 3.14d is a Double
● Groovy truth: null, “”, [], 0 are false
– if (!thing) println “thing was null”
– if (!str) println “str was empty”
● Groovy == means .equals
– For identity use a.is(b)

12.
Property Access
● Everything is public
by default
● Every field has a
getter and setter by
default
● Gotcha’s
– Map access
– String.class->String
● Property access automatically
uses getters and setters
● foo.bar == foo.getBar()
● foo.bar = 2 == foo.setBar(2)

13.
Lists and Maps
● def emptyList = [ ]
● def emptyMap = [:]
● def numList = [1,2,3]
● def strMap = [cars: 1, boats: 2, planes: 3]
● def varMap = [(var1): 1, (var2): 2, (var3): 3]

14.
Maps Continued...
● def map = [cars: 1, boats: 2, planes: 3]
● String key access: map.cars
● OR map[‘cars’]
● Also works for modifying:
– map.cars = 42
– map[‘cars’] = 42

15.
Code Demo

16.
A better switch
● Switch can use types, lists, ranges, patterns…
Switch (x) {
case Map: println “was a map”; break
case [4,5,6]: println “was 4, 5 or 6”; break
case 0..20: println “was 0 to 20”; break
case ~/w+/: println “ was a word”; break
case “hello”: println x; break
case BigDecimal: println “was a BigDecimal”

17.
Groovy GDK
● Adds methods to everything! Adds its own classes...
● Collections: sort, findAll, collect, inject, each,…
● IO: toFile(), text, bytes, withReader, URL.content
● Ranges: x..y, x..<y
– GetAt syntax for Strings and Lists:
● text[0..4] == text.substring(0,5)
● Utilities: ConfigSlurper, Expando, ObservableList/Map/Set

18.
Safe dereference & Elvis operator
● Safe dereference ?.
– String name = person?.name
– Java: person == null ? null : person.getName()
● Elvis operator ?:
– String name = person?.name ?: “Bob”
– Java: if (name == null) name = “Bob”

19.
Closures
● Closure: “a self-containing method” (like Lambda exp.)
– def say = { x -> println x }
– say(‘hello gr8conf’)
– def say = { println it }
– def adder = { x, y -> x + y }
● Closures have several implicit variables:
– it - If the closure has one argument
– this - Refers to the enclosing class
– owner - The same as this unless it is enclosed in another closure.
– delegate - Usually the same as owner but you can change it (this
allows the methods of delegate to be in scope).

20.
Closures Continued...
● When used as last parameter, closure can go
outside parentheses
– methodCalled(param1, param2) { closureHere() }
– methodWithOnlyClosure { closureHere() }

21.
Regex Pattern Matching
● Regex = regular expressions
● Within forward slashes / is a regex
– You don’t need to use double
● =~ for matching anywhere within a string
– if (text =~ /d+/) println “there was a number in it”
● ==~ for matching the whole string
– if (email ==~ /[w.]+@[w.]+/) println “it’s an email”

22.
Meta-programming
● Every class and instance has a metaClass
● String.metaClass.upper =
{ delegate.toUpperCase() }
– “foo”.upper() == “FOO”
● Traits can be used as
mixins
● Maps can be cast to
actual types using as
[bark: {println “Woof!”}]
as Dog

23.
Code Demo

24.
Other Surprises for Java Devs
● Default values for method parameters
● groovy.transform.*
– @EqualsAndHashCode
– @TupleConstructor
– @ToString
– @Canonical
● Generics not enforced by default

25.
Advanced Groovy
● Groovy Design Patterns
– Strategy pattern
– Categories
– Method caching
● DSLs – Domain Specific Languages
– Operator Overloading
● Traits
● Functional Programming
– curry

26.
Spock
Grails
Gradle grooscript
The Groovy Ecosystem
and many others….
Griffon

27.
Gradle
Imperative, not declarative
Relies on plugins
Tasks
Vanilla groovy
Easy to build plugins
Easy to do sub-projects

28.
Spock
Built on JUnit
Somewhat enhanced groovy
“test names can be any string”
given: when: then: expect:
Built-in mocking
Table-syntax for provided test data
Pretty assert output

29.
Thanks!
Adam L. Davis
“Learning Groovy”
github.com/adamldavis
/2017-gr8conf-learning-groovy
adamldavis.com
@adamldavis
groocss.org
@groocss
How? Gedit + https://github.com/aeischeid/gedit-grails-bundle