It is Java as it should be. Easy and intuitive, it offers new features unknown to its parent yet, and come up with those benefits that form the basis of the DSLs

Giancarlo Frison

Groovy Overview

Groovy is a super vision of Java. It can leverage Java’s enterprise capabilities but also has closures and dynamic typing, without all ceremonial syntax needed in Java

● Introduction● Data types ● Language features● Closures● Meta programming

What is Groovy?

Groovy = Java – boiler plate code+ mostly dynamic typing

+ closures+ domain specific languages

Introduction

● Fully Object oriented● Closures: reusable and

assignable piece of code● Groovy Beans● Collection Literals (lists,

maps, ranges, regular expressions)

● Meta programming (MOP, Expando, AST transformations, Mixins/Categories)

● Gpath expressions ● Grep and switch● Builders (XML, Json, Swing,

Ant, Tests)● Additional operators (? Null

safe)● Default and named

arguments● String enhances● Osgi

Groovy Overview

● Grails Web framework inspired by Ruby on Rails

● Gradle The next generation build system

● Griffon Desktop framework inspired by Grails

● Grape Add dependencies to your classpath

● Gorm Grails ORM persistance framework

● Gpars Concurrency/parallelism library

Frameworks

Less tedious syntax

A better Java…

…a better Java…

…a better Java…

…a better Java…

…a better Java…

…a better Java…

…a better Java…

…a better Java.

Better JavaBeans…

…a better JavaBeans…

…a better JavaBeans.

Data Types

● Multi-line stringsdef tt = '''

She sells, sea shellsBy the sea shore''‘

● String interpolationdef fullname = “$name $surname”

● Regexsassert'-36'==~ ‘/^[+-]?\d+$/’

GStrings● Rangesassert fullname[0..5] == name

● Comparison operatorsa==b a +-* ba<=>b a[]

● Groovy-gdkhttp://groovy.codehaus.org/groovy-jdk/java/lang/String.html

● Literal syntaxlist = [3,new Date(),’Jan']assert list + list == list * 2

● Mapsmap = [a:1,b:2]assert map['a']==1 && map.b ==2

● Rangesdef ls = ‘a'..'z‘,nums = 0..<10assert ls.size+nums.size == 36

Collections● Overloading operatorslist << new Date()

● Loop closuresmap.each{key, value ->

println “$key : $value”}

● …loop closureseach, every, collect, any, inject, find, findAll,upto, downto, times, grep, reverseEach, eachMatch, eachWithIndex, eachLine eachFile, eachFileMatch…

● No more :BigDecimal.divide(BigDecimal right, <scale>,

BigDecimal.ROUND_HALF_UP)

● Insteadassert 1/2 == new java.math.BigDecimal("0.5")

Math operations

use ( groovy.time.TimeCategory ) { println 1.minute.from.now println 10.hours.ago println new Date() - 3.months

def duration = date1 - date2 println "days: ${duration.days}, Hours: ${duration.hours}"}

Dates

Language Features

● It can handle any kind of valueswitch (x) { case 'James':

break case 18..65:

break case ~/Gw?+e/:

break case Date:

break case ['John', 'Ringo', 'Paul', 'George']:

break default:}

Improved Switch

● Any expression could be used and evaluated whereas Java requires a boolean.

● Number 0 return false● Empty string, lists, maps, matchers return false● Null objects return false● Of course… boolean false return false

Groovy Truth

● Null-safe version of Java's '.' operator

people << new Person(name:'Harry')

biggestSalary = people.collect{ p -> p.job?.salary }.max()

println biggestSalary

Null Object Pattern

send(String from, String to, String subject, String body) { println "sender ${from}" println "sender ${to}" println "sender ${subject}" println "sender ${body}"}

send from:"john@example.com", to:"mike@example.com", subject:"greetings", body:"Hello Goodbye"

Named arguments

def (a, b, c) = [10, 20, 'foo']assert a == 10 && b == 20 && c == 'foo‘

def geocode(String location) { // implementation returns [48.824068, 2.531733]}def (lat, long) = geocode(“Bassano del Grappa, Italia")

Multiple assignments

● expression language integrated into Groovy which allows parts of nested structured data to be identified.

● a.b.c -> for XML, yields all the <c> elements inside <b> inside <a>

def feed = new XmlSlurper().parse('http://gfrison.com/rss')println feed.channel.item[0].title

● a.b.c -> all POJOs, yields the <c> properties for all the <b> properties of <a> (sort of like a.getB().getC() in JavaBeans)

GPath

Closures

● Treats data structures and operations as Objectsdef clos = { println "hello!" }clos()

● Closures as method argumentsdef houston = {doit ->

(10..1).each{ count->doit(count)

}} houston{ println it }

Closures

● Groovy has 3 variables inside each closure for defining different classes in his scope:

● this: As in Java it refers to the closure itself.● owner: Enclosing object of the closure.● delegate: The same of the owner, but it can be replaced

● When a closure encounters a method call that it cannot handle itself, it automatically relays the invocation to its owner object. If this fails, it relays the invocation to its delegate.

Closure delegate

Closures for better design…

…more better design.

Meta Object Programming

● Runtime● ExpandoMetaClass● Closures● Categories

● Compile-time● AST Transformations

Groovy MOP

● Allow to dynamically add methods, properties…

String.metaClass.swapCase = {-> def sb = new StringBuffer() delegate.each { sb << (Character.isUpperCase(it as char) ? Character.toLowerCase(it as char) : Character.toUpperCase(it as char)) } sb.toString()}

println "hELLO wORLD".swapCase()

ExpandoMetaClass

● It is a container for everything added by developer

def bean = new Expando( name:"James", location:"London", id:123 )assert "James" == bean.nameassert 123 == bean.id

Expando

● Add functionalities to classes to make them more usableclass StringCategory { static String lower(String string) { return string.toLowerCase() }} use (StringCategory) { assert "test" == "TeSt".lower()}

use (groovy.time.TimeCategory ) { println 1.minute.from.now println 10.hours.ago println new Date() - 3.months}

Categories

● Grape@Grab('org.mortbay.jetty:jetty-embedded:6.1.0')def server = new Server(8080)println "Starting Jetty, press Ctrl+C to stop."server.start()

● Slf4j@Slf4jclass HelloWorld { def logHello() { log.info 'Hello World' }}

AST Examples

● compile-time metaprogramming capabilities allowing powerful flexibility at the language level, without a runtime performance penalty.

● Global transformations adding a jar● Local transformations by annotating code elements:@Immutable @Delegate @Log @Field @PackageScope @AutoClone @AutoExternalizable @ThreadInterrupt @TimedInterrupt @ConditionalInterrupt @ToString @EqualsAndHashCode @TupleConstructor @Canonical @InheritConstructors @WithReadLock @WithWriteLock @ListenerList @Singleton @Lazy @Newify @Category@Mixin @PackageScope @Grab @Bindable @Vetoable

AST Transformations

Giancarlo Frison - gfrison.com

Questions?

…and Happy coding!