This document introduces Groovy, a scripting language for Java. It discusses how Groovy compiles to Java bytecode and can be used with existing Java tools and libraries. Examples show how Groovy simplifies common tasks like iteration, exception handling, and building XML/HTML. The document also briefly introduces Grails, a web framework that uses Groovy's conventions to accelerate development.

1. Groovy: a Scripting
Language for Java
Charles Anderson
Western Skies Consulting
cander@westernskiesweb.com

2. Outline
• Introduction and Context
• Stupid Pet Tricks
• Using Groovy in a Java project
• Conclusion
• Grails?

3. Introduction
• There are now many dynamic and/or
scripting languages that run on the Java
Platform
• Groovy is a scripting language specifically for
the Java Platform - feature-rich, Java-friendly
• Groovy compiles to Java classes & byte
code - can use all of Java Platform

4. Introduction
• Scripting - don’t have to explicitly compile
• Typing - static or dynamic (optional/duck)
• Mature - version 1.5, 1.6 Beta 2
• Books, websites, commercial backing, JSR
• IDE Support

5. Code Comparison
Groovy Groovy
Java Java
Syntax Functionality

6. Java or Groovy?
class Book {
private String title;
Book (String theTitle) {
title = theTitle;
}
String getTitle() {
return title
}
}

7. Stupid Pet Tricks
public class Main {
public static void main(...)
System.out.println(“Hello
World”);
}}
println ‘Hello World’

8. More Powerful Switch
switch (x) {
case 0: // single int
case 1..9: // range
case [11,13,17]: // list
case Float: // type check
case ‘cat’: // string
case ~/[A-Z][0-9]/: //regexp
}

9. Groovy Beans
public class MyBean implements
Serializable {
private String myProp;
public String getMyProp()...
public void setMyProp(...)...
}
class MyBean implements Serializable {
String myProp;
}

10. Terse NPE Safety
if (x!=null && x.y!=null) {
z = x.y.z;
}
z = x?.y?.z

11. Bob the Builder
writer = new FileWriter(‘bob.html’)
def page = new MarkupBuilder(writer)
page.html{
head { title ‘An HTML Page’ }
body {
h1 ‘The big heading’
form (action:’submit’) {
input(type:’checkbox’, id:’yes’)
input(type:’checkbox’, id:’no’)
}}}

12. Closures
• A closure is a chunk of code that is a first-
class entity/object in the language
• From functional programming
• Can accept parameters and return a value
• Typical Java solution: inner classes, visitor
pattern, template method pattern

13. Exorcising Inner
Classes
t = new Thread(new Runable() {
public void run() {
// some code
}});
t.start();
Thread.start { //some code }

14. Java Iteration
for (Iterator it=coll.iterator();
it.hasNext(); ) {
Item item=(Item)it.next();
//some code
}
for (Item item : coll) {
// some code
}

15. Groovy Iteration
coll.each(item-> // some code)
coll.findAll(it % 2 == 0).each(...)
new File(‘foo.txt’).eachLine {
println it }

16. Embrace and Extend
• Groovy “extends” Java classes - GDK
• Object, GString, Collections, Files,
Threads, Beans
• Groovy enhances existing Java tools
• JUnit, Ant, Swing
• Reduce tedious boiler-plate - DRY

17. using Groovy
• Little development tasks - automation
• Can script COM and Windows
• Experiments and spiking
• Testing - unit tests, data loading, scaffolding

18. Conclusion
• Groovy is a dynamic scripting language that
is designed specifically for Java
• Lots of “tricks” to make life easier, but they
can be introduced gradually
• Groovy is a playground for the future of
Java - e.g., closures, properties
• Questions, job leads, Grails?

19. Grails: Groovy on Rails
• Accelerate and simplify web development
on the Java Platform - but not Java Language
• Deploys as a WAR file
• MVC structure
• Convention over configuration
• Uses Spring and Hibernate under covers

20. Grails Commands
Usage: grails command
create-app
run-app
create-domain-class Entity
generate-all Entity
generate-webtest
run-webtest
war