Introduction to Groovy

October 3, 2015

by Jenn Strater

@jennstrater

Current

http://jlstrater.github.io/intro-groovy-osn

Slides(source)

About Me

Professional

Senior Consultant - Object Partners
Co-Founder - Gr8Ladies

About Me

Experience

source: http://tjvantoll.com/2014/12/29/so-you-want-to-write-a-tech-book/

About Me

Minneapolis, MN

Twitter @jennstrater
LinkedIn https://linkedin.com/in/jennstrater
Github https://github.com/jlstrater

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

Groovy

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

Open Source

Apache

http://groovy-lang.org

To contribute: https://github.com/apache/incubator-groovy

The Groovy Ecosystem

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

Download Locally

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

SDK Manager (formerly GVM)http://sdkman.io/
```
curl -s get.sdkman.io | bash
```

Groovy Shell

Groovy Console

Web Console

http://groovyconsole.appspot.com/

Things to Remember

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

Hello, World!

groovy>println "Hello, Open Source North!"

Hello, Open Source North!
===>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

Lists

(examples in console)

definition
get/set values
append
multiply

List m = ['a', 'b', 2]
println m[2]
-> 2

m[2] = 3
println m
-> [a, b, 3]

m << 'c'
println m
-> [a, b, 3, c]

m.push(4)
-> [a, b, 3, c, 4]

m.pop()
-> 4

List m = ['a', 'b', 2]

m.multiply(2)
 -> ['a', 'b', 2, 'a', 'b', 2]
 
m * 2
 -> ['a', 'b', 2, 'a', 'b', 2]
 
m + 2
 -> ['a', 'b', 2, 2]

Maps

(examples in console)

definition
get/set values
get all keys/values

Map m = [val1: 'a', val2: 'b', val3: 2]

println m.val1
 -> a
println m['val3']
 -> 2
 
m.val4 = 3
println m
 -> [val1:a, val2:b, val3: 2, val4: 3]
 
println m.keySet()
 -> [val1, val2, val3, val4]
 
println m.values()
 -> [a, b, 2, 3]

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]

Functions

Integer timesTwo(x) {
  x + x
}

Flexible, familiar syntax
Optional

Parenthesis when calling functions
Parameter typing
return statements

println timesTwo(10)
 -> 20
def result = timesTwo 10
println result
 -> 20

Closures

Code as Data

(to the console)

definition
calls

Closure c = { name, year = 2015 ->
  println "Hello, $name $year!"
}

c.call('Open Source North')
-> "Hello, Open Source North 2015!"

c('Open Source North', 2016)
-> "Hello, Open Source North 2016"

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!

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

is verifies object identity

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

-> 1
-> 2
-> 3

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

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

Every

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

Object Oriented Programming (OOP)

class Person {
  String first
  String last
}

Person me = new Person(first: 'Jenn', last: 'Strater')
println me.first
println me.last

-- add String company to class --
me.company = 'Object Partners'
println me.properties
-> [class:class Person, first:Jenn, company:Object Partners, last:Strater]

class Person {
  String first
  String last
  
  String getFullName() {
    this.first + ' ' + this.last
  }
}

Person me = new Person(first: 'Jenn', last: 'Strater')
println me.fullName
 -> 'Jenn Strater'

Scripts

(save previous script as people.groovy)

groovy people.groovy
-> Jenn Strater

Script Parsing

println doubledValue(10)

def doubledValue(x) {
  x * 2
}

File Processing

Creating and Writing to Files

def myFile = new File('foo.txt')
myFile.write 'Hello, \n'
myFile.append('Open Source North!')

foo.txt

Hello,
Open Source North!

Reading Files

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

 -> Hi,
 -> Open Source North!

APIs

(copy to console)

@Grab(group='org.codehaus.groovy.modules.http-builder', module='http-builder', version='0.7.1')
import groovyx.net.http.RESTClient
def http = new RESTClient("http://www.gr8ladies.org")
http.get(path: '/api/companies') { resp, reader ->
  reader.sort { -it.percentageTotalWomen } // sort by percentage women in descending order
  reader[0..4].each{ // only the first 5
    if(it.totalEmployees) { // if the value of total employees is not 0 (to eliminate companies that didn't report that field)
      println 'name:' + it.name
      println 'country:' + it.country
      println 'total employees: ' + it.totalEmployees
      println 'total men: '+ it.totalMen
      println 'total women: '+ it.totalWomen + '\n'
    }
  }
}
return null // don't print the entire result at the end

APIs

(copy to console)

@Grab(group='org.codehaus.groovy.modules.http-builder', module='http-builder', version='0.7.1')

import groovyx.net.http.RESTClient

def http = new RESTClient("http://api.icndb.com")

http.get(path: '/jokes/random/5', query: [exclude: 'explicit']) { resp, reader ->
  reader.value.joke.each{
    println it + '\n'
  }
}

Other Cool Groovy Things

Regex
MetaClass
Groovy for Android
Compile Static Annotation

Conclusions

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

References

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

Questions?

@jennstrater

jenn@gr8ladies.org