Intro to Groovy

J. David Beutel

2013-03-18

Presenter's Background

1991 Comp. Sci. BS from RIT

1996- using Java

2000- developing web apps in Java

2005- staff at UH ITS/MIS

2009- using Groovy

2010- app with Groovy/Grails/Geb/Spockin production since 2012 June

LOC: 14K production, 13K test

Presentation Objectives

recognize and understand Groovy code

get interested in Groovy coding

(not introducing Spock/Geb/Grails yet)

Outline

What is Groovy?

Why do I care?

How is it different?

How can I use it?

What is Groovy?

dynamic extension of Javasyntax

API (GDK)

enables less code, more clarity

compiles to Java classes

seamless integration with Java

backed by SpringSource/VMware

good IDE support inIntelliJ IDEA (the best, IMHO)

Eclipse Groovy/Grails (Spring) Tool Suite

Syntax

optional

;

( )

public

return

catch

types

literal

String'foo'

List['foo', 'bar']

Map[name: 'David', age: 43]

Range3..7

regex Pattern~/\d+/

multi-line String'''helloworld'''

keyword

in

as

def

featureexample

propertiesassert URL.'package'.name == 'java.net'

Closureolder = employees.findAll {it.age > 39}

GString$name was ${age - 1} years old last year

Groovy truthassert age

yet another for loopfor (e in employees) {totalAge += e.age}

named paramse = new Employee(name: 'David', age: 43)

multiple assignments(first, last) = 'John Doe'.tokenize()

Syntax

featureexample

default importsjava.io.*, java.lang.*, java.net.*, java.util.*

negative/range indexeslast = employees[-1]; allButLast = employees[0..-2]

dynamic propertiesobj[propertyName]

dynamic methodsobj.$methodName(params)

meta-programmingInteger.metaClass.cos 39}

findObjectfirstOlder = employees.find {it.age > 39}

anyBooleanhasOlder = employees.any {it.age > 39}

everyBooleannoYounger = employees.every {it.age > 39}

eachvoiddef totalAge = 0employees.each {totalAge += it.age}

eachWithIndexvoidemployees.eachWithIndex { e, i -> println ${e.name} is at index $i}

grep(classifier)Listdavids = employees*.name.grep ~/David.*/

collectListtripleAges = employees.collect {it.age * 3}

API (GDK)

method on Filereturnsexample

eachFile(closure)voidnew File('somedir').eachFile {println it}

getText()Stringpid = new File('app.pid').text.toLong()

readLines()Listlines = new File('grammar').readLines()

eachLine(closure)Objectfile.eachLine {parse(it)}

withWriter(closure)Objectnew File('report').withWriter {out -> employees.each {it.write(out)}}

on Stringreturnsexample

split()String[]assert 'a b c'.split() == ['a', 'b', 'c']

tokenize(token)Listassert '/tmp:/usr'.tokenize(':') == ['/tmp', '/usr']

normalize()Stringassert 'a\r\nb'.normalize() == 'a\nb'

find(regex)Stringassert 'New York, NY 10292-0098'.find(/\d{5}/) == '10292'

Why do I care?

My 1st job after college was programming client/server apps in C and X Windows on Unix, for 6 years. Java was released towards the end, and I loved its exceptions, safe memory, garbage collection, and simpler API. Memory management and error handling in C took so much time programming around and debugging, while Java did it automatically or more cleanly, that I couldn't stand C anymore. For example, compare error handling in C with Exceptions in Java...

Example: Exceptions

C

Java

Java's journey

versyearfeatureexample

1.01996initial release1.11997inner classesHibernateTemplate hibernateTemplate = new HibernateTemplate(sessionFactory);List products = (List) hibernateTemplate.execute( new HibernateCallback() { public Object doInHibernate(Session session) throws HibernateException { return session.find(FROM example.Product WHERE price > ?, new Integer(1000), Hibernate.INTEGER); } });

reflectiontry { Class c = Class.forName("Foo"); c.getMethod("hello").invoke(c.newInstance());

} catch (ClassNotFoundException e) { e.printStackTrace();}catch (InvocationTargetException e) { e.printStackTrace();}catch (NoSuchMethodException e) { e.printStackTrace();}catch (InstantiationException e) { e.printStackTrace();}catch (IllegalAccessException e) { e.printStackTrace();}

other new APIJDBC, RMI

Java's journey

versyearfeatureexample

1.21998CollectionsList stooges = Arrays.asList(new String[] {Larry, Moe, Curly});

1.32000dynamic proxiesFoo f = (Foo) Proxy.newProxyInstance(Foo.class.getClassLoader(), new Class[] { Foo.class }, handler);

other new APIJNDI, JPDA

1.42002assertassert 1 + 1 == 2

regexassert Pattern.compile("\\d{5}").matcher("12345").matches();

other new APINIO, logging, XML, XSLT, JAXP, JCE, JSSE, JAAS

1.52004genericsList stooges = Arrays.asList(new String[] {"Larry", "Moe", "Curly"});

annotations@Override public String toString() { return foo; }

enumsenum HolidayType {UH, STATE, BANK, FEDERAL}

varargsList stooges = Arrays.asList("Larry", "Moe", "Curly");

autoboxingList ages = Arrays.asList(43, 35, 28);

for each loopfor (String s : stooges) { System.out.println(s + " says \"Nyuk nyuk.\""); }

static importsimport static org.apache.commons.lang.StringUtils.*;

Java's journey

versyearfeatureexample

1.62006scripting languagesScriptEngineManager factory = new ScriptEngineManager();ScriptEngine engine = factory.getEngineByName("JavaScript");try { engine.eval("print('Hello, World')");} catch (ScriptException e) { e.printStackTrace();}

other new APIJAX-WS (SOAP), JAXB

1.72011Strings in switchswitch(artistName) { case Lily Allen: return FABULOUS; case Elisa: return GREAT; default: return MEH;}

generic type inferenceMap myMap = new HashMap();

catch multiple typescatch (IOException|SQLException ex) { logger.log(ex); throw ex;}

Why do I care?

Why do I care?

Why do I care?

How is it different?

code comparison, Java versus Groovy

hello worlds

examples from my Timesheets project

How is it different?

How is it different?

How is it different?

How is it different?

How can I use it?

same as Java

scripts, e.g.groovy -e "println System.properties['user.home']"

groovy -e 'println java.sql.Timestamp.valueOf("2012-11-17 06:49:33").time'

web app stats polling daemon via JMX

JUnit -> Spock

Selenium -> Geb

Spring/Hibernate -> Grails

Usage: JUnit -> Spock

Usage: Selenium -> Geb

Usage: Spring/Hibernate -> Grails

For more about Groovy

groovy.codehaus.org

google, e.g., groovy collection

books

Let's make beautiful code!

Thanks for coming!