1. Practical Groovy
for Java Developers
Gabriel Dogaru
gabi@gabrieldogaru.com
March 10 2012

2. Agenda
Groovy introduction
Closures
First Script
Testing with Groovy
Building with groovy

3. What is groovy?
“Groovy is what Java would look like had it been
written in the 21st century.”
An agile and dynamic language for the JVM
Inspired by languages like Python, Ruby and
Smalltalk
Compiles straight to Java bytecode
Compiled or interpreted
Supports Domain-Specific Languages and other
compact syntax

4. A programming language is for thinking
about programs, not for expressing
programs you've already thought of. It
should be a pencil, not a pen.
Paul Graham

5. I think I know java!
//... Person.java //... Person.groovy
//... Person.groovy
public class Person { public class Person {
private String name; class Person { name;
private String
private int age; String name
private int age;
int age
public Person() { public Person() {
}
} }
public Person(String name, int age) { public Person(String name, int age) {
this.name = name; //... Person.groovyname;
this.name =
this.age = age; class Person { age;
this.age =
} }
def name
public String getName() { def ageString getName() {
public
return name; } return name;
} }
public void setName(String name) { person = new Person(name: "Ion", age: 66)
public void setName(String name) {
this.name = name; this.name = name;
} //person.setAge(61)
}
person.age = 61
public int getAge() { public int getAge() {
return age; return age;
//System.out.println(person.getName())
} }
println person.name
public void setAge(int age) { public void setAge(int age) {
this.age = age; //> Ionthis.age = age;
} }
} }

6. Gotchas
 Automatic Imports
 Everything is an object
 Optional data type declaration (Duck
Typing)
 Optional exception handling
 Optional semicolons and parentheses
 Optional return statements
 Operator overloading

7. Groovy Closures
 Like a "code block" or a method pointer
 May be passed as arguments
 May accept arguments
 May return values
 Makes anonymous inner classes obsolete

8. Closures
//... ClosureExample.java
//... ClosureExample.java //... ClosureExample.groovy
import com.google.common.base.Predicate;
import java.util.ArrayList; import com.google.common.base.Predicate;
import com.google.common.collect.Iterables;
import java.util.Arrays; import com.google.common.collect.Iterables;
import java.util.ArrayList; import java.util.ArrayList;
def numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]
import java.util.List;
import java.util.Arrays; import java.util.Arrays;
def oddNumbers = numbers.findAll {it % 2!=0}
import java.util.List; import java.util.List;
public class ClosureExample { oddNumbers.each {println it}
public static void main(String[] args) {
public class ClosureExample { public class ClosureExample {
List<Integer> numbers = Arrays.asList(
public static void main(String[] args) { public static void main(String[] args) {
List<Integer> numbers = 2, 3, 4, 5, 6, 7, 8, 9);
1, Arrays.asList( List<Integer> numbers = Arrays.asList(
1, 2, 3, 4, 5, 6, 7, 8, 9); 1, 2, 3, 4, 5, 6, 7, 8, 9);
List<> oddNumbers = new ArrayList<..>();
Iterable<> number : numbers) {
for (int oddNumbers=Iterables.filter(numbers, Iterable<> oddNumbers=Iterables.filter(numbers,
new Predicate<Integer>() {
if (number % 2 != 0) { new Predicate<Integer>() {
def odd = {Integer n->
public boolean apply(Integer number) {
oddNumbers.add(number); public boolean apply(Integer number) {
return return number % 2 != 0;
n%2 != 0
} return number % 2 != 0;
} } } }
}); });
for (int number : oddNumbers) { def numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9]
for (int number : oddNumbers) { for (int number : oddNumbers) {
System.out.println(number);
System.out.println(number); def oddNumbers = numbers.findAll odd
System.out.println(number);
}} oddNumbers.each {println it}
}
}
} }
}
} }

9. Cooo...ol
How do I start ?

10. Write your first script
//… WriteSomeXML .java
@GrabResolver(name = 'maven-central', root = 'repo1.maven.org')
import java.io.File;
@Grapes(
import java.io.FileOutputStream;
import javax.xml.parsers.*;
@Grab(group = 'xerces', module = 'xercesImpl', version = '2.10.0')
)//… write xml
import org.w3c.dom.*;
import org.apache.xml.serialize.*;
public class WriteSomeXML {
new File("persons.xml").withWriter {writer ->
import javax.xml.parsers.* {
public static void main(String[] args)
def xml = new MarkupBuilder(writer)
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
import org.apache.xml.serialize.*
xml.persons db = null;
DocumentBuilder {
dbf Document doc = null;
= DocumentBuilderFactory.newInstance()
db = {person(id: 99) {
trydbf.newDocumentBuilder()
db = dbf.newDocumentBuilder();
doc = firstname("John")
db.newDocument()
doc = db.newDocument(); <?xml version="1.0" encoding="UTF-8"?>
root = lastname("Smith")
doc.createElement"persons“
Element root = doc.createElement("persons");
<persons>
doc.appendChild root
}}} doc.appendChild(root);
Element el = doc.createElement("person"); <person id="99">
el = doc.createElement"person“
root.appendChild(el);
root.appendChild "99"); <firstname>John</firstname>
el.setAttribute("id", el
el.setAttribute "id", doc.createElement("firstname");
Element firstname = "99“
<lastname>Smith</lastname>
//… read xml
el.appendChild(firstname);
firstname = doc.createElement("firstname") </person>
firstname.appendChild(doc.createTextNode("John")); </persons>
el.appendChild firstname
def parser lastname =XmlParser()
Element = new doc.createElement("lastname");
firstname.appendChild doc.createTextNode("John")
el.appendChild(lastname);
def persons = parser.parse("persons.xml")
lastname.appendChild(doc.createTextNode("Smith"));
lastname = doc.createElement "lastname“
println "${persons.person[0].@id}"
OutputFormat out = new OutputFormat(doc);
el.appendChild lastnamelastname.appendChild
out.setIndenting(true);
persons.person.eachnew XMLSerializer(new FileOutputStream(new File("persons.xml")), out);
doc.createTextNode="Smith" ->
XMLSerializer xmlSer { person
out println person.firstname[0].text()
=xmlSer.serialize(doc);
new OutputFormat doc
} catch (Exception e) {
out.indenting = true
} e.printStackTrace();
xmlSer = new XMLSerializer(new FileOutputStream(new File("persons.xml")),
} out)
xmlSer.serialize doc
}
}

11. Write your tests with groovy
<dependency>
<groupId>org.codehaus.groovy</groupId>
<artifactId>groovy</artifactId>
<scope>test</scope>
</dependency>
....
<build>
<plugins>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<compilerId>groovy-eclipse-compiler</compilerId>
</configuration>
<dependencies>
<dependency>
<groupId>org.codehaus.groovy</groupId>
<artifactId>groovy-eclipse-compiler</artifactId>
</dependency>
</dependencies>
</plugin>
....

12. Classes under test
//… ExchangeRateDAO.java
public interface ExchangeRateDAO {
BigDecimal load(String currency);
void save(String currency, BigDecimal value);
}
//… ExchangeRateService.java
public class ExchangeRateService {
private final ExchangeRateDAO rateDAO;
public ExchangeRateService(ExchangeRateDAO rateDAO) {
this.rateDAO = rateDAO;
}
public BigDecimal getRate(String currency) {
return rateDAO.load(currency);
}
public void updateRate(String currency, BigDecimal value) {
rateDAO.save(currency, value);
}
}

13. Mocking – map coercion
//… DynamicTest.groovy
class DynamicTest {
@Test
public void test1() {
ExchangeRateDAO rateDAO = {1.0} as ExchangeRateDAO
ExchangeRateService service = new ExchangeRateService(rateDAO)
assertEquals 1.0, service.getRate("USD")
}
@Test(expected = IllegalAccessError.class)
public void test_named_methods() {
ExchangeRateDAO rateDAO = [
load: {String v -> 1.0},
save: {String k, BigDecimal v -> throw new IllegalAccessError()}
] as ExchangeRateDAO
ExchangeRateService service = new ExchangeRateService(rateDAO)
assertEquals 1.0, service.getRate("USD")
service.updateRate("1", 2)
}
}

14. Mocking - MockFor
//… MockForTest.groovy
class MockForTest {
@Test
public void test() {
def mockContext1 = new MockFor(ExchangeRateDAO)
mockContext1.demand.load("USD") { 1.0 }
def dummyDAO = mockContext1.proxyDelegateInstance()
def service = new ExchangeRateService(dummyDAO)
assertEquals 1.0, service.getRate("USD")
mockContext1.verify dummyDAO
}
}

15. Build with groovy
<?xml version="1.0" encoding="UTF-8"?>
<project name=“Ant Example" default="main" basedir=".">
<property environment="env"/>
<taskdef name="groovy" classname="org.codehaus.groovy.ant.Groovy">
<classpath>
<fileset dir="${env.GROOVY_HOME}" includes="embeddable/groovy-all-
*.jar,lib/ivy*.jar"/>
</classpath>
</taskdef>
<target name=“print-xml">
<groovy>
xmlfiles = new File('.').listFiles().findAll{ it =~ '.xml$' }
xmlfiles.sort().each{ println it.toString() }
</groovy>
</target>
</project>

16. Build with Ant
def ant = new AntBuilder()
ant.echo(file:'Temp.java',
''' class Temp { public static void main(String[] args) {System.out.println("Hello"); }}
''')
ant.javac(srcdir:'.', includes:'Temp.java', fork:'true')
ant.java(classpath:'.', classname:'Temp', fork:'true')
ant.echo('Done')
// =>
// [javac] Compiling 1 source file
// [java] Hello
//[echo] Done

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