Prepared exclusively for Larry Cormier What Readers Are Saying About Modular Java Craig Walls does an awesome job in this book covering th i s very important topic. Whether you are developing an enterprise application or an application to run on y our cell phone, modularization is some- thing you have to master, and I can’t think of a better resource than this book you’re holding in your hands. Dr. Venkat Subramaniam Jolt award–winning author and founder of Agile Developer, Inc. Well-written and interesting. I found the “hands-on” style engaging. It feels like you are in an OSGi workshop, tr ying out all the tools and looking at the results. . . well done, Craig! Frederic Daoud Author, Stripes. . . And Java Web Development Is Fun Again Craig does a great job covering the “why” and “how” of writing modu- lar Java web applications with OSGi in this book. Erik Weibust Senior architect, Credera Craig takes what many believe to be a complex subject and str i ps away the FUD immediately and then goes on to show the power and elegance of OSGi, especially when enabled with Spring for building enterprise-class Java applications. By making OSGi and Spring more accessible to Java developers everywhere, Craig does a great service to his whole industry, and I plan to continue to be part of the wave of developers building modular and flexible applications with these technologies! Perhaps the best proof of this book’s value is the fact that it was immediately practical and applicable to me in a real-world project, even before it was fully written! This will be the go-to book for developers looking to take full advantage of these advances in software development. Mike Nash President, JGlobal Ltd. Prepared exclusively for Larry Cormier Craig’s style is fun and easy to read, while he tackles very technical material. This book demystifies a topic that even experienced devel- opers struggle with. Even if you don’t program in J ava, this book will improve your design thinking in how to better use components. Derek Lane CTO, Semantra, Inc. Craig has done it again! As he has in the past with technologies such as the Spring Framework, he has masterfully crafted a book that is clear, concise, and comprehensive. Developers and archi tects alike will find this to be an invaluable tool as they take Java modularization t o the next level. Paul Nelson Software craftsman Prepared exclusively for Larry Cormier Prepared exclusively for Larry Cormier Modular Java Creating Flexible Applications with OSGi and Spring Craig Walls The Pragmatic Bookshelf Raleigh, North Carolina Dallas, Texas Prepared exclusively for Larry Cormier Many of the design ations used by manufacturers and sellers to distinguish thei r prod- ucts are claimed as trademarks. Where those designations appear in this book, and The Pragmatic Programmers, LLC wa s aware of a trademark claim, the designations have been printed in initial capital letters or in all c apitals. The Pragmatic Starter Kit, The Pragmatic Programmer, Pragmatic Programming, Pragmatic Bookshelf and the linking g device are trademarks of The Pragmatic Programmers, LLC. 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 © 2 009 Craig Walls. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmit- ted, in any form, or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior consent of the publisher. Printed in the United States of America. ISBN-10: 1-934356-40-9 ISBN-13: 978-1934356-40-1 Printed on acid-free paper. P1.0 printing, May 2009 Version: 2009-6-24 Prepared exclusively for Larry Cormier Contents 1 Introduction 10 1.1 A New Set of Wheels . . . . . . . . . . . . . . . . . . . . 11 1.2 Modularity . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.3 Introducing OSGi . . . . . . . . . . . . . . . . . . . . . . 15 1.4 Road Map . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 1.5 Who Is This Book For? . . . . . . . . . . . . . . . . . . . 21 1.6 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 21 I OSGi Fundamentals 23 2 Getting Started 24 2.1 Getting to Know the OSGi Container . . . . . . . . . . . 24 2.2 Hello, OSGi . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2.3 A H ello World Service Bundle . . . . . . . . . . . . . . . 36 3 Dude, Where’s My JAR? 45 3.1 Searching for JAR Files . . . . . . . . . . . . . . . . . . . 45 3.2 Designing the Application Components . . . . . . . . . 46 3.3 Bundling the Application Components for OSGi . . . . 48 3.4 Setting Up the Project . . . . . . . . . . . . . . . . . . . 50 4 Working with Bundles 59 4.1 Creating the Domain Bundle . . . . . . . . . . . . . . . 59 4.2 Contending with Nonbundle Dependencies . . . . . . . 69 4.3 Following the Bundle Life Cycle . . . . . . . . . . . . . . 78 5 OSGi S ervices 80 5.1 Creating an OSGi Service . . . . . . . . . . . . . . . . . 80 5.2 Testing the Service . . . . . . . . . . . . . . . . . . . . . 91 5.3 Consuming OSGi Services . . . . . . . . . . . . . . . . . 100 Prepared exclusively for Larry Cormier CONTENTS 8 II Spring Dynamic Modules and Web Bundles 109 6 Spring and OSGi 110 6.1 Introducing Spring-DM . . . . . . . . . . . . . . . . . . . 111 6.2 Declaring Services . . . . . . . . . . . . . . . . . . . . . . 115 6.3 Injecting Services into Consumers . . . . . . . . . . . . 122 7 Creating Web Bundles 129 7.1 Assembling a Web Server . . . . . . . . . . . . . . . . . . 129 7.2 The Spring-DM Web Extender . . . . . . . . . . . . . . . 137 7.3 Developing a Web Bundle . . . . . . . . . . . . . . . . . 142 7.4 Deploying the Web Bundle . . . . . . . . . . . . . . . . . 150 8 Extending Bundles 159 8.1 Introducing Fragments . . . . . . . . . . . . . . . . . . . 159 8.2 Creating a UI Fragment . . . . . . . . . . . . . . . . . . 161 8.3 Trying It . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 III Finishing Touches 171 9 OSGi in Production 172 9.1 Distributing the Application . . . . . . . . . . . . . . . . 172 9.2 Adding an Administration Console . . . . . . . . . . . . 181 10 Configuring the Application 186 10.1 Installing Pax ConfMan . . . . . . . . . . . . . . . . . . . 187 10.2 Configuring the Web Console . . . . . . . . . . . . . . . 188 10.3 Adjusting Logging . . . . . . . . . . . . . . . . . . . . . . 190 10.4 Configuring Application Details . . . . . . . . . . . . . . 191 10.5 Configuring the Web S erver . . . . . . . . . . . . . . . . 197 A Manifest Headers 202 A.1 OSGi R4 Headers . . . . . . . . . . . . . . . . . . . . . . 202 B Spring-DM Configuration 204 B.1 Spring-DM Core Configuration Element s . . . . . . . . 204 B.2 Spring-DM Compendium Configuration E l ements . . . 212 Report erratum this copy is (P1.0 printing, May 2009) Prepared exclusively for Larry Cormier CONTENTS 9 C The OSGi Blueprint Service 216 C.1 Comparing the Blueprint Service with Spring-DM . . . 216 C.2 OSGi Blueprint Services (RFC-124) Element s . . . . . . 217 C.3 OSGi Blueprint Services (RFC-124) Compendium Ele- m ents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 D Resources 231 E Bibliography 233 Index 234 Report erratum this copy is (P1.0 printing, May 2009) Prepared exclusively for Larry Cormier Chapter 1 Introduction Welcome to the world of modular J ava! Building and deploying monolithic applications is a thing of the past. Applications that are composed of several smaller, well-defined modules are a much better way to go. By hiding design and implementat i on details that are likely to change behind a stable API, each module is easier to maintain, test, and understand. This ultimately affects the overall maintainability and testability of the w hole application. Unfortunately, as of Java 6, Java’s built-in facilities for modularity are severely limited. Imperative instructions are modularized i nto methods, which are then modularized into classes. Classes can be further col- lected into packages, which offer a weak form of modularization. But that’s where Java modularity ends. Java offers no means for modular- izing classes or packages of classes i nto coarse-grained modules. Where Java falls short, OSGi steps in. OSGi is a framework specifica- tion 1 that brings modularity to the Java platform. In this book we’re going to see how OSGi can enable development of well-defined, loosely coupled modules that can be assembled into complete applications. But before we get too carried away, let’s get a feel for the type of problem that OSGi solves by listening in on a conversation between two co- workers on their way to lunch. 1. You can download the OSGi framework and service compendium specifications from http://www.osgi.org/Specifications/HomePage. Prepared exclusively for Larry Cormier [...]... The boundaries provided by JAR files are artificial and fade away at runtime But what about Java? Does Java offer any help in developing modular applications? Modularity in Java Java archive (JAR) files are often thought of as the unit of modularity in Java Unfortunately, however, JAR files give only a thin illusion of modularity A typical JAR file is really only a deployment-time convenience, providing a... originally installed In addition, the security layer may support Java 2–style permissions to control loading and executing bundle classes How Does OSGi Address Modularity Concerns? When we considered Java s built-in support for modularity, we determined that it came up short Now let’s examine the features of OSGi to see how it brings modularity to the Java platform Content Hiding In OSGi, each bundle is loaded... in the bundle’s manifest It should be noted that OSGi is not a silver bullet for modularity Just adopting OSGi into your application architecture will not necessarily make your application more modular It is still up to you to ensure that the modules you create follow good modular design OSGi does, however, encourage modular programming practices by making it easy to create well-defined modules and,... can begin Finally, the system is maintained in modular fashion; system errors and deficiencies can be traced to specific system modules, thus limiting the scope of detailed error searching Most programming languages offer some degree of support for modularity There are even some legacy programming languages such as Modula-2 and MIL that were created with modularity as a core concern Report erratum Prepared... moving to a new house Jim: Really? You hadn’t mentioned that Brian: Well, it was a recent decision A lightbulb burned out in our kitchen, and so 1.2 Modularity Brian’s problem is lack of modularity—or more precisely, his failure to recognize his car’s modularity Cars are not monoliths—they are made up of several distinct and individual components It’s typically Report erratum Prepared exclusively for... brings modularity to the Java platform OSGi enables the creation of highly cohesive, loosely coupled modules that can be composed into larger applications What’s more, each module can be individually developed, tested, deployed, updated, and managed with minimal or no impact to the other modules Let’s take a look at the ingredients that make up the OSGi 4.1 specification and see how they support modular. .. and see how they support modular application development in Java The Key Elements of OSGi From Figure 1.2, on the next page, you can see that OSGi builds upon the Java platform with a module definition, module life cycle, service registry, services, and security layers At its lowest level, the OSGi specification defines a deployment model for Java- based modules The unit of deployment in OSGi is known as... (P1.0 printing, May 2009) 15 I NTRODUCING OSG I Services Service Registry Lifecycle Modules Java Virtual Machine Security Application/Bundles OSGi Java Platform Operating System Hardware Figure 1.2: The OSGi framework provides a life cycle for modules, a service registry, and a compendium of services for building modular applications file contains OSGi-specific metadata, including a definitive name, version,... application into two or more individually built projects Those are all great things But if your application is so modular, then why do you still deploy it as one big monolithic WAR file? I submit that your applications aren’t as modular as you probably think they are What Does It Mean to Be Modular? Put simply, a module is a self-contained component of a much larger system Beyond that trite definition,... probably won’t come as much of a surprise that modularity is not a new idea It’s a common tactic in the manufacture of all kinds of systems, software or otherwise In fact, in their 1970 book (see Designing Systems Programs [GP70]), Richard Gauthier and Stephen Ponto summarize the benefits of modularity: A well-defined segmentation of the project effort ensures system modularity Each task forms a separate, distinct . fade away at runtime. But what about Java? Does Java offer any help in developing modular applications? Modularity in Java Java archive (JAR) files are often. packages, which offer a weak form of modularization. But that’s where Java modularity ends. Java offers no means for modular- izing classes or packages of