Intro to the Groovy Language and Ecosystem

About Me

About YOU

• Students
• Professional Developers
• Java
• .NET
• PHP or Ruby
• JRuby, Scala, or Clojure
• Groovy

Agenda

• Background & Ecosystem
• Getting Started
• Concepts
• Data Types
• Collections/Loops
• Functions
• Closures

Agenda

• Object Oriented Programming (OOP)
• Scripting
• File Processing
• APIs
• MetaProgramming

Groovy

• Dynamic, compiled language for the Java Virtual Machine(JVM).
• OPTIONALLY typed
• Interoperable with existing Java libraries
• Concise, easy to read code
• Ability to be statically compiled
• Used by many major companies including:
  • 
  • 
  • 
  • 
  • 
  • 

source: http://www.groovy-lang.org

Open Source

http://groovy-lang.org

https://github.com/apache/groovy

The Groovy Ecosystem

• Grails
• Griffon
• Gradle

• Spock and Geb
• Ratpack
• And Many More!

When to use Groovy

• existing Java libraries
• developers know Java or another JVM language
• infrastructure to support JVMs
• quick prototyping
• scripting
• writing tests

When Not to use Groovy

• lots of legacy code in another language
• need 'bare metal' level performance

Getting Started

• SDK Manager (formerly GVM)http://sdkman.io/

  curl -s get.sdkman.io | bash
  sdk install groovy

• Download Locally

  http://groovy-lang.org/download.html

Groovy Shell

Groovy Console

Web Console

http://groovyconsole.appspot.com/

Things to Remember

1. There is more than one way to do almost anything.
2. It's probably optional.
   • semi-colons
   • typing
   • parenthesis around parameters
   • getters and setters
   • return statements
3. By default, the last command executed is what's returned.

Hello, World!

groovy>println "Hello, DevFest Berlin 2017!"

Hello, DevFest Berlin 2017!
===>null

Data Types

• Optional Typing, NOT dynamic
• treated as objects
• int treated like Integer

int i = 10
println i.class.name
 -> java.lang.Integer
 
Integer i = 20
println i.class.name
 -> java.lang.Integer

def

when no type is specified or for a flexible type

def i = 10
println i * 2
 -> 20
 
i = 'abc'
println i * 2
 -> abcabc

Strings

(examples in console)

• Single Quoted
• Double Quoted
• Multi-line

Collections

Ranges

println (1..10)
  -> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

println (1..<10)
  -> [1, 2, 3, 4, 5, 6, 7, 8, 9]

Loops and Special Functions

• Basic For Loop
• Each
• Collect
• Spread Dot

Basic Loops

List dl = []

for(Integer i = 1; i < 4; i++){
  dl.add(i * 2)
}

println dl
 -> [2, 4, 6]

List dl = []

for(i in [1,2,3]) {
  dl << i * 2
}

println dl
 -> [2, 4, 6]

Each

List sl = [1, 2, 3]
List dl = []
sl.each { it ->
  dl << it * 2
}
println dl
-> [2, 4, 6]

Collect

Map m = [va1: 1, var2: 2, var3: 3]

List dl = m.collect { key, value ->
  value * 2
}

println dl
 -> [2, 4, 6]

Spread Dot

(1..3).multiply(2) -> [1, 2, 3, 1, 2, 3](1..3)*.multiply(2) -> [2, 4, 6]

Try It!

Let's groovy-fy this code

List l = [-1,2,-3,-17]
List al = []
for ( i in l ) {
  al << i.abs()
}
println al
--> [1,2,3,17]

[-1,2,-3,-17]*.abs()

Try It!

Print the sum of the numbers from 1 to 10

option 1:
Integer answer = 0
for(i in [1,2,3,4,5,6,7,8,9,10]) {
  answer += i
}
println answer
option 2:
Integer answer = 0
(1..10).each {
  answer = answer + it
}
println answerbonus answer:
println ( (1..10).sum() )

Groovy Truth

False values

• null
• Empty Set
• Empty String
• Zero

Equality

== verifies value same as .equals()

is verifies object identity

List numbers = [0,1,2,3]
numbers.each {
  if(it) {
    println it
  }
}

-> 1
-> 2
-> 3

Identity

Integer myInteger = 2
int myInt = 2

myInteger.is(myInt)

-> true

Identity

String world = 'World'
GString myGString = "Hello, $world"
String myString = 'Hello, World'

println myGString
println myString

myGString.is(myString)

-> Hello, World
-> Hello, World
-> false

Other Groovy Operators

• Ternary Operator

x ? return x : return 'something else'

• Elvis Operator

x ?: 'something else'

• Null Safe

myMap?.propertyA?.propertyB

Search

Map m = [val1: 2, val2: 4, val3: 6]

m.find { it.value % 2 == 0 && it.value % 3 != 0 }
-> val1=2

m.findAll {it.value % 2 == 0 && it.value % 3 != 0 }
-> [val1:2, val2:4]

Other List Methods

• Any

Map m = [val1: 2, val2: 4, val3: 6]
m.any { it.value % 2 == 0 }
-> true

• Every

m.every { it.value % 3 == 0 }
-> false

Scripts

(save previous script as people.groovy)

groovy people.groovy
-> Jane Doe

Scripts

println doubledValue(10)

def doubledValue(x) {
  x * 2
}

AST Viewer

Reading Files

def myFile = new File('foo.txt')
myFile.eachLine { line ->
  def processedLine = line.replaceAll('Hello', 'Hi')
  println processedLine
}

 -> Hi,
 -> DevFest Berlin!

MetaProgramming

Extending a class

Number.metaClass.getDollars = { delegate as BigDecimal }

Number.metaClass.getProperty = { String name ->
  def rates = [euros: 1.1f, pesos: 0.063f]
  delegate * (rates[name] as BigDecimal)
}

Adding different currencies together

def total = 20.dollars + 40.euros + 200.pesos
assert total == 76.60

MetaProgramming

Dynamic Methods

class Person {
  def methodMissing(String name, args) {
    if (name.startsWith('say')) {
      String message = (name - 'say').trim()
      println message
    }
  }
}

Trying out our dynamic method

Person you = new Person()
you.sayHello()
you."say You are awesome!"()

Other Cool Groovy Things

• Regex
• Groovy for Android
• Compile Static Annotation
• Domain Specific Language (DSL)s

Your first app

sdk use gradle 4.3

Your first app

gradle init --type=groovy-application

Your first app

(example in IntelliJ)

• Main
• Spock Test
• Build, Test, and Run with Gradle

Conclusions

Groovy
• provides the benefits of the JVM platform
• adds features to enhance productivity over Java
• is similar to other languages such as Ruby and Python

Resources

• Groovy in Action, 2nd Edition
• groovy-lang.org
• Practical Groovy Free e-book

Questions?