Programming Groovy dynamic productivity for the java developer phần 1 docx

As I read the book, I asked my own“why?” question over and over: “Why wasn’t this book around when Iwas learning Groovy?” After you’ve read this book, it’s difficult to look at programmi

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 ject programming, unit testing with mocks, and DSLs This is a must-have reference for any developer interested in learning to programdynamically

metaob-Joe McTee

Developer, JEKLsoft

Venkat does a fantastic job of presenting many of the advanced tures of Groovy that make it so powerful He is able to present thoseideas in a way that developers will find very easy to internalize Thisbook will help Groovy developers take their kung fu to the next level.Great work, Venkat!

fea-Jeff Brown

Member, the Groovy and Grails development teams

At this point in my career, I am really tired of reading books thatintroduce languages This volume was a pleasant breath of fresh air,however Not only has Venkat successfully translated his engagingspeaking style into a book, he has struck a good balance betweenintroductory material and those aspects of Groovy that are new andexciting Java developers will quickly grasp the relevant conceptswithout feeling like they are being insulted Readers new to the plat-form will also be comfortable with the arc he presents

This book is an important step forward in mastering the language.Venkat takes the reader beyond simple keystrokes and syntax intothe deep depths of “why?” Groovy brings a subtle sophistication tothe Java platform that you didn’t know was missing Once you seethose missing language features in action, you can’t imagine how youever programmed without them As I read the book, I asked my own

“why?” question over and over: “Why wasn’t this book around when Iwas learning Groovy?” After you’ve read this book, it’s difficult to look

at programming on the Java platform the same way

Scott Davis

Editor-in-Chief, aboutGroovy.com; author of Groovy Recipes

Venkat neatly dissects the Groovy language—a language that is farmore 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 dynamiclanguages on top of the Java Virtual Machine, look no further thanVenkat’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 theirtoolkit, and Venkat does a tremendous job presenting this excitingnew addition to the JVM With all of his examples, you’ll be up andrunning in no time!

Nathaniel T Schutta

Author/Speaker/Teacher

I am always on the lookout for good books on the metaprogrammingfeatures of languages, and Groovy finally has one Part 3 of Venkat’sbook 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, pletely devoid of fluff, that will get you on the path to Groovy goodnessright out of the gate.

com-David Geary

Author, Clarity Training, Inc

Venkat could make rocket science sound easy He definitely makesGroovy for Java developers sound easy

Erik Weibust

Senior Architect, Credera

Programming Groovy Dynamic Productivity for the Java Developer

Venkat Subramaniam

The Pragmatic Bookshelf

Raleigh, North Carolina Dallas, Texas

Many of the designations used by manufacturers and sellers to distinguish their ucts are claimed as trademarks Where those designations appear in this book, and The Pragmatic Programmers, LLC was aware of a trademark claim, the designations have been printed in initial capital letters or in all capitals The Pragmatic Starter Kit, The Pragmatic Programmer, Pragmatic Programming, Pragmatic Bookshelf and the linking g device are trademarks of The Pragmatic Programmers, LLC.

prod-Every precaution was taken in the preparation of this book However, the publisher assumes no responsibility for errors or omissions, or for damages that may result from the use of information (including program listings) contained herein.

Our Pragmatic courses, workshops, and other products can help you and your team create better software and have more fun For more information, as well as the latest Pragmatic titles, please visit us at

http://www.pragprog.com

Copyright © 2008 Venkat Subramaniam.

All rights reserved.

No part of this publication may be reproduced, stored in a retrieval system, or ted, in any form, or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior consent of the publisher.

transmit-Printed in the United States of America.

ISBN-10: 1-934356-09-3

ISBN-13: 978-1-934356-09-8

Printed on acid-free paper with 50% recycled, 15% post-consumer content.

— Thiruvalluvar, Poet and Philosopher, 31 B.C.

(Verse 426 from Thirukural, a collection of 1330 noble couplets)

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

4.1 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

CONTENTS 11

8.1 Object Extensions 141

8.2 Other Extensions 147

9 Working with XML 155 9.1 Parsing XML 155

9.2 Creating XML 160

10 Working with Databases 164 10.1 Connecting to a Database 165

10.2 Database Select 166

10.3 Transforming Data to XML 167

10.4 Using DataSet 168

10.5 Inserting and Updating 169

10.6 Accessing Microsoft Excel 169

11 Working with Scripts and Classes 172 11.1 The Melting Pot of Java and Groovy 172

11.2 Running Groovy 173

11.3 Using Groovy Classes from Groovy 174

11.4 Using Groovy Classes from Java 175

11.5 Using Java Classes from Groovy 176

11.6 Using Groovy Scripts from Groovy 178

11.7 Using Groovy Scripts from Java 180

11.8 Ease of Integration 182

III MOPping Groovy 183 12 Exploring Meta-Object Protocol (MOP) 184 12.1 Groovy Object 185

12.2 Querying Methods and Properties 190

12.3 Dynamically Accessing Objects 192

13 Intercepting Methods Using MOP 194 13.1 Intercepting Methods Using GroovyInterceptable 194

13.2 Intercepting Methods Using MetaClass 197

CONTENTS 12

14.1 Injecting Methods Using Categories 203

14.2 Injecting Methods Using ExpandoMetaClass 208

14.3 Injecting Methods into Specific Instances 212

14.4 Method Synthesis Using methodMissing 214

14.5 Method Synthesis Using ExpandoMetaClass 219

14.6 Synthesizing Methods for Specific Instances 222

15 MOPping Up 224 15.1 Creating Dynamic Classes with Expando 224

15.2 Method Delegation: Putting It All Together 227

15.3 Review of MOP Techniques 231

16 Unit Testing and Mocking 234 16.1 Code in This Book and Automated Unit Tests 234

16.2 Unit Testing Java and Groovy Code 236

16.3 Testing for Exceptions 240

16.4 Mocking 241

16.5 Mocking by Overriding 244

16.6 Mocking Using Categories 248

16.7 Mocking Using ExpandoMetaClass 249

16.8 Mocking Using Expando 251

16.9 Mocking Using Map 253

16.10 Mocking Using the Groovy Mock Library 254

17 Groovy Builders 260 17.1 Building XML 260

17.2 Building Swing 264

17.3 Custom Builder Using Metaprogramming 265

17.4 Using BuilderSupport 268

17.5 Using FactoryBuilderSupport 272

18 Creating DSLs in Groovy 277 18.1 Context 277

18.2 Fluency 279

18.3 Types of DSLs 280

18.4 Designing Internal DSLs 281

18.5 Groovy and DSLs 281

18.6 Closures and DSLs 282

18.7 Method Interception and DSLs 283

18.8 The Parentheses Limitation and a Workaround 285

18.9 Categories and DSLs 286

18.10 ExpandoMetaClass and DSLs 289

CONTENTS 13

Back in 2003, when we started Groovy, our goal was to provide Javadevelopers with an additional language to complement Java, a newSwiss Army knife to add to their tool belt Java is a great language and

a wonderful platform, but sometimes you need the agility and siveness of scripting languages or, even better, dynamic languages Wedidn’t want a new language that would be a paradigm shift for Javadevelopers Instead, Groovy was made to seamlessly integrate with Java

expres-in all possible ways while at the same time addexpres-ing all the goodiesyou would expect from a dynamic language The best of both worlds!You don’t even have to wait for Java 7, 8, or 9 to get all the nuggetsyou’d want to have in your next programming language of choice: clo-sures, properties, native syntax for lists, maps, and regular expres-sions Everything is already there

Over the course of time, Groovy has matured a lot and has become avery successful open source dynamic language used by tons of Javadevelopers and by big companies that embed it in their applicationsservers or their mission-critical applications Groovy lets you write moreexpressive unit tests and simplifies XML parsing or SQL data imports,and for your mundane tasks, there’s a scripting solution perfectly inte-grated with your Java ecosystem When you need to extend your appli-cation to customize it to your needs, you can also integrate Groovy

at specific points by injecting Groovy scripts Thanks to Groovy’s leable syntax, you can even create domain-specific languages fairly eas-ily to represent business rules that even end users can author

mal-Now, step back a little At first sight, despite the marketing taint ofthe previous paragraphs, it sounds great, and you probably see a fewplaces where you’d definitely need to use such a versatile tool But it’sjust something else you have to learn to be able to leverage it to itsfullest extent, right? You’re a Java developer, so do you fear it’s going

to be difficult to get the best out of it without wasting too much of yourtime and energy?

FOREWORD 15

Fortunately, this book is right for you Venkat will guide you through

Groovy and its marvels Without being a boring encyclopedia, this book

covers a lot of ground And in a matter of hours (well, in fact, just the

time to read the book), you’ll be up to speed, and you’ll see how Groovy

was made by Java developers for Java developers You won’t regret your

journey, and you’ll be able to keep this book on your desk for reference

or for finding new creative ways to solve the problem of the day

Guillaume Laforge (Groovy project manager)

February 5, 2008

Chapter 1

Introduction

As a busy Java developer, you’re constantly looking for ways to be moreproductive, right? You’re probably willing to take all the help you canget from the platform and tools available to you When I wax poeticabout the “strength of Java,” I’m not talking about the language or itssyntax It’s the Java platform that has become more capable and moreperformant To reap the benefit of the platform and to tackle the inher-ent complexities of your applications, you need another tool—one with adynamic and metaprogramming capabilities Java—the language—hasbeen flirting with that idea for a while and will support these features

to various degrees in future versions However, you don’t have to waitfor that day You can build performant Java applications with all thedynamic capabilities today, right now, using Groovy

Dynamic languages have the ability to extend a program at runtime,including changing the structure of objects, types, and behavior Dy-namic languages allow you to do things at runtime that static languages

do at compile time; they allow you to execute program statements thatwere created on the fly at runtime

For example, if you want to get the date five days from now, you canwrite this:

5.days.from.now

Yes, that’s your friendly java.lang.Integer chirping dynamic behavior inGroovy, as you’ll learn later in this book

WHYDYNAMICLANGUAGES? 17

The flexibility offered by dynamic languages gives you the advantage

of evolving your application as it executes You are probably familiar

with code generation and code generation tools I consider code

gener-ation to be soooo 20th century In fact, generated code is like an

inces-sant itch on your back; if you keep scratching it, it turns into a sore

With dynamic languages, there are better ways I prefer code

synthe-sis, which is in-memory code creation at runtime Dynamic languages

make it easy to “synthesize code.” The code is synthesized based on the

flow of logic through your application and becomes active “just in time.”

By carefully applying these capabilities of dynamic languages, you can

be more productive as an application developer This higher

productiv-ity means you can easily create higher levels of abstractions in shorter

amounts of time You can also use a smaller, yet more capable, set

of developers to create applications In addition, greater productivity

means you can create parts of your application quickly and get

feed-back from your fellow developers, testers, domain experts, and

cus-tomer representatives And all this leads to greater agility.1

Dynamic languages have been around for a long time, so you may be

asking, why is now a great time to get excited about them? I can answer

that with four reasons:2

• Machine speed

• Availability

• Awareness of unit testing

• Killer applications

Let’s discuss each of these reasons for getting excited about dynamic

languages, starting with machine speed Doing at runtime what other

languages do at compile time first raises the concern of the speed of

dynamic languages Furthermore, interpreting code at runtime rather

than simply executing compiled code adds to that concern Fortunately,

machine speed has consistently increased over the years—handhelds

have more computing and memory power today than what large

com-puters had decades ago Tasks that were quite unimaginable using a

1 Tim O’Reilly observes the following about developing web applications: “Rather than

being finished paintings, they are sketches, continually being redrawn in response to

new data.” He also makes the point that dynamic languages are better suited for these in

“Why Scripting Languages Matter” (see Appendix A , on page 291 ).

2 A fifth reason is the ability to run dynamic languages on the JVM, but that came

much later.