Programming Groovy Dynamic Productivity for the Java Developer

303 Pages·2008·10.166 MB·English

by  Venkat Subramaniam

What readers are saying about Programming Groovy
More than a tutorial on the Groovy language, Programming Groovy is
an excellent resource for learning the advanced concepts of metaob-
ject programming, unit testing with mocks, and DSLs. This is a must-
have referencefor any developer interested in learning to program
dynamically.
Joe McTee
Developer, JEKLsoft
Venkat does a fantastic job of presenting many of the advanced fea-
tures of Groovy that make it so powerful. He is able to present those
ideas in a way that developers will find very easy to internalize. This
book will help Groovy developers take their kung fu to the next level.
Great work, Venkat!
Jeff Brown
Member, the Groovy and Grails development teams
At this point in my career, I am really tired of reading books that
introduce languages. This volume was a pleasant breath of fresh air,
however. Not only has Venkat successfully translated his engaging
speaking style into a book, he has struck a good balance between
introductory material and those aspects of Groovy that are new and
exciting. Java developers will quickly grasp the relevant concepts
without feeling like they are being insulted. Readers new to the plat-
formwill also be comfortable with the arc he presents.
Brian Sletten
Zepheira, LLC
You simply won’t find a more comprehensive resource for getting up to
speed on Groovy metaprogramming.
Jason Rudolph
Author, Getting Started with Grails
This book is an important step forward in mastering the language.
Venkat takes the reader beyond simple keystrokes and syntax into
the deep depths of “why?” Groovy brings a subtle sophistication to
the Java platformthat you didn’t know was missing. Once you see
those missing language features in action, you can’t imagine how you
ever programmed without them. As I read the book, I asked my own
“why?” question over and over: “Why wasn’t this book around when I
was learning Groovy?” After you’ve read this book, it’s difficult to look
at programming on the Java platformthe same way.
Scott Davis
Editor-in-Chief, aboutGroovy.com; author of Groovy Recipes
Venkat neatly dissects the Groovy language—a language that is far
more than just “Java++”—in nice, edible chunks for the Groovy pro-
grammer to consume. If you’re a Java programmer and you’re try-
ing to figure out why everybody is getting all excited about dynamic
languages on top of the Java Virtual Machine, look no further than
Venkat’s book.
Ted Neward
Java/.NET/XML services, http://www.tedneward.com
Despite signs to the contrary, Java isn’t dead—it’s just evolving.
Today’s developer needs a dynamic language like Groovy in their
toolkit, and Venkat does a tremendous job presenting this exciting
new addition to the JVM. With all of his examples, you’ll be up and
running in no time!
Nathaniel T. Schutta
Author/Speaker/Teacher
I am always on the lookout for good books on the metaprogramming
features of languages, and Groovy finally has one. Part 3 of Venkat’s
book is devoted entirely to Groovy’s metaprogramming features.
Sweet. I won’t tell you which language to use, but if you are consid-
ering Groovy, read Part 3 of this book.
Stuart Halloway
CEO, Relevance, Inc.
www.thinkrelevance.com
This is a very well-written guide to Groovy. It’s an easy read, com-
pletely devoid of fluff, that will get you on the path to Groovy goodness
right out of the gate.
David Geary
Author, Clarity Training, Inc.
Venkat could make rocket science sound easy. He definitely makes
Groovy for Java developers sound easy.
Erik Weibust
Senior Architect, Credera
Programming Groovy
Dynamic Productivity for the Java Developer
Venkat Subramaniam
The Pragmatic Bookshelf
Raleigh,NorthCarolina Dallas,Texas
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Pragmatic Programmers, LLC was aware of a trademark claim, the designations have
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Copyright©2008VenkatSubramaniam.
Allrightsreserved.
Nopartofthispublicationmaybereproduced,storedinaretrievalsystem,ortransmit-
ted, in any form, or by any means, electronic,mechanical,photocopying, recording, or
otherwise,withoutthepriorconsentofthepublisher.
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ISBN-10:1-934356-09-3
ISBN-13:978-1-934356-09-8
Printedonacid-freepaperwith50%recycled,15%post-consumercontent.
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“As moves the world, to move in tune with
changing times and ways is wisdom”
— Thiruvalluvar, Poet and Philosopher, 31 B.C.
(Verse426 fromThirukural, acollection of 1330 noble couplets)

Contents
Foreword 14
1 Introduction 16
1.1 Why Dynamic Languages? . . . . . . . . . . . . . . . . . 16
1.2 What’s Groovy? . . . . . . . . . . . . . . . . . . . . . . . 19
1.3 Why Groovy? . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.4 What’s in This Book? . . . . . . . . . . . . . . . . . . . . 23
1.5 Who Is This Book For? . . . . . . . . . . . . . . . . . . . 26
1.6 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 26
I Beginning Groovy 29
2 Getting Started 30
2.1 Getting Groovy . . . . . . . . . . . . . . . . . . . . . . . . 30
2.2 Installing Groovy . . . . . . . . . . . . . . . . . . . . . . 31
2.3 Test-Drive Using groovysh . . . . . . . . . . . . . . . . . 32
2.4 Using groovyConsole . . . . . . . . . . . . . . . . . . . . 33
2.5 Running Groovy on the Command Line . . . . . . . . . 34
2.6 Using an IDE. . . . . . . . . . . . . . . . . . . . . . . . . 35
3 Groovy for the Java Eyes 37
3.1 From Java to Groovy . . . . . . . . . . . . . . . . . . . . 37
3.2 JavaBeans . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3.3 Optional Parameters . . . . . . . . . . . . . . . . . . . . 50
3.4 Implementing Interfaces . . . . . . . . . . . . . . . . . . 51
3.5 Groovy boolean Evaluation . . . . . . . . . . . . . . . . 55
3.6 Operator Overloading . . . . . . . . . . . . . . . . . . . . 56
3.7 Support of Java 5 Language Features . . . . . . . . . . 59
3.8 Gotchas . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
CONTENTS 10
4 Dynamic Typing 75
4.1 Typing in Java . . . . . . . . . . . . . . . . . . . . . . . . 75
4.2 Dynamic Typing . . . . . . . . . . . . . . . . . . . . . . . 78
4.3 Dynamic Typing != Weak Typing . . . . . . . . . . . . . 79
4.4 Design by Capability . . . . . . . . . . . . . . . . . . . . 80
4.5 Optional Typing . . . . . . . . . . . . . . . . . . . . . . . 86
4.6 Types in Groovy . . . . . . . . . . . . . . . . . . . . . . . 86
4.7 Multimethods . . . . . . . . . . . . . . . . . . . . . . . . 87
4.8 Dynamic: To Be or Not to Be? . . . . . . . . . . . . . . . 91
5 Using Closures 92
5.1 Closures . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
5.2 Use of Closures . . . . . . . . . . . . . . . . . . . . . . . 96
5.3 Working with Closures . . . . . . . . . . . . . . . . . . . 98
5.4 Closure and Resource Cleanup . . . . . . . . . . . . . . 98
5.5 Closures and Coroutines . . . . . . . . . . . . . . . . . . 101
5.6 Curried Closure . . . . . . . . . . . . . . . . . . . . . . . 102
5.7 Dynamic Closures . . . . . . . . . . . . . . . . . . . . . . 105
5.8 Closure Delegation . . . . . . . . . . . . . . . . . . . . . 107
5.9 Using Closures . . . . . . . . . . . . . . . . . . . . . . . 110
6 Working with Strings 111
6.1 Literals and Expressions . . . . . . . . . . . . . . . . . . 111
6.2 GString Lazy Evaluation Problem . . . . . . . . . . . . . 114
6.3 Multiline String . . . . . . . . . . . . . . . . . . . . . . . 118
6.4 String Convenience Methods . . . . . . . . . . . . . . . 120
6.5 Regular Expressions . . . . . . . . . . . . . . . . . . . . 121
7 Working with Collections 124
7.1 Using List. . . . . . . . . . . . . . . . . . . . . . . . . . . 124
7.2 Iterating Over an ArrayList. . . . . . . . . . . . . . . . . 126
7.3 Finder Methods . . . . . . . . . . . . . . . . . . . . . . . 129
7.4 Collections’ Convenience Methods . . . . . . . . . . . . 130
7.5 Using Map . . . . . . . . . . . . . . . . . . . . . . . . . . 133
7.6 Iterating Over Map . . . . . . . . . . . . . . . . . . . . . 135
7.7 Map Convenience Methods. . . . . . . . . . . . . . . . . 137