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OSGi in Action
CREATING MODULAR APPLICATIONS IN JAVA
RICHARD S. HALL
KARL PAULS
STUART McCULLOCH
DAVID SAVAGE
MANNING
Greenwich
(74° w. long.)
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v
brief contents
PART 1 INTRODUCING OSGI: MODULARITY, LIFECYCLE, AND SERVICES 1
1 ■ OSGi revealed 3
2 ■ Mastering modularity 24
3 ■ Learning lifecycle 69
4 ■ Studying services 117
5 ■ Delving deeper into modularity 154
PART 2 OSGI IN PRACTICE . 189
6 ■ Moving toward bundles 191
7 ■ Testing applications 230
8 ■ Debugging applications 258
9 ■ Managing bundles 292
10 ■ Managing applications 319
PART 3 ADVANCED TOPICS 343
11 ■ Component models and frameworks 345
12 ■ Advanced component frameworks 373
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BRIEF CONTENTS
vi
13 ■ Launching and embedding an OSGi framework 412
14 ■ Securing your applications 438
15 ■ Web applications and web services 477
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vii
contents
foreword xiv
preface xvii
acknowledgments xix
about this book xx
about the authors xxv
PART 1 INTRODUCING OSGI: MODULARITY, LIFECYCLE,
AND SERVICES 1
1
OSGi revealed 3
1.1 The what and why of OSGi 4
Java’s modularity limitations 5
■
Can OSGi help you? 8
1.2 An architectural overview of OSGi 9
The OSGi framework 9
■
Putting it all together 12
1.3 “Hello, world!” examples 12
Module layer example 12
■
Lifecycle layer example 14
■
Service
layer example 16
■
Setting the stage 18
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CONTENTS
viii
1.4 Putting OSGi in context 19
Java Enterprise Edition 19
■
Jini 20
■
NetBeans 20
■
Java
Management Extensions 20
■
Lightweight containers 21
■
Java
Business Integration 21
■
JSR 277 21
■
JSR 294 22
■
Service
Component Architecture 22
■
.NET 22
1.5 Summary 23
2
Mastering modularity 24
2.1 What is modularity? 25
Modularity vs. object orientation 25
2.2 Why modularize? 27
2.3 Modularizing a simple paint program 28
2.4 Introducing bundles 31
The bundle’s role in physical modularity 32
■
The bundle’s role in
logical modularity 33
2.5 Defining bundles with metadata 34
Human-readable information 35
■
Bundle identification 36
Code visibility 39
■
Class-search order 48
2.6 Finalizing the paint program design 50
Improving the paint program’s modularization 51
■
Launching
the new paint program 52
2.7 OSGi dependency resolution 53
Resolving dependencies automatically 53
■
Ensuring consistency
with uses constraints 59
2.8 Reviewing the benefits of the modular paint program 64
2.9 Summary 68
3
Learning lifecycle 69
3.1 Introducing lifecycle management 70
What is lifecycle management? 70
■
Why lifecycle management? 72
3.2 OSGi bundle lifecycle 72
Introducing lifecycle to the paint program 73
■
The OSGi
framework’s role in the lifecycle 75
■
The bundle activator manifest
entry 76
■
Introducing the lifecycle API 77
■
Lifecycle state
diagram 83
■
Bundle cache and framework restarts 84
3.3 Using the lifecycle API in your bundles 85
Configuring bundles 86
■
Deploying bundles 88
■
Inspecting
framework state 92
■
Persisting bundle state 93
■
Listening for
events 96
■
Bundle suicide 99
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CONTENTS
ix
3.4 Dynamically extending the paint program 101
3.5 Lifecycle and modularity 108
Resolving bundles 108
■
Refreshing bundles 110
■
When
updating isn’t updated 114
3.6 Summary 115
4
Studying services 117
4.1 The what, why, and when of services 118
What is a service? 118
■
Why use services? 119
■
When to use
services 123
■
When not to use services 124
■
Still not sure? 124
4.2 OSGi services in action 125
Publishing a service 126
■
Finding and binding services 128
4.3 Dealing with dynamics 132
Avoiding common pitfalls 133
■
Listening for services 136
Tracking services 141
4.4 Using services in the paint example 143
Defining a shape service 144
■
Publishing a shape service 144
Tracking shape services 145
4.5 Relating services to modularity and lifecycle 146
Why can’t I see my service? 147
■
Can I provide a bundle-specific
service? 147
■
When should I unget a service? 148
■
When
should I unregister my service? 148
■
Should I bundle interfaces
separately? 149
4.6 Standard services 149
Core services 150
■
Compendium services 151
4.7 Summary 152
5
Delving deeper into modularity 154
5.1 Managing your exports 155
Importing your exports 155
■
Implicit export attributes 158
Mandatory export attributes 160
■
Export filtering 161
Duplicate exports 162
5.2 Loosening your imports 164
Optional imports 164
■
Dynamic imports 165
■
Optional vs.
dynamic imports 166
■
Logging example 167
5.3 Requiring bundles 171
Declaring bundle dependencies 171
■
Aggregating split
packages 173
■
Issues with bundle dependencies 176
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CONTENTS
x
5.4 Dividing bundles into fragments 177
Understanding fragments 177
■
Using fragments for
localization 180
5.5 Dealing with your environment 183
Requiring execution environments 184
■
Bundling native
libraries 185
5.6 Summary 187
PART 2 OSGI IN PRACTICE 189
6
Moving toward bundles 191
6.1 Turning JARs into bundles 192
Choosing an identity 192
■
Exporting packages 195
Discovering what to import 199
■
Embedding vs. importing 203
Adding lifecycle support 204
■
JAR file to bundle cheat sheet 205
6.2 Splitting an application into bundles 206
Making a mega bundle 206
■
Slicing code into bundles 216
Loosening things up 221
■
To bundle or not to bundle? 226
6.3 Summary 229
7
Testing applications 230
7.1 Migrating tests to OSGi 231
In-container testing 231
■
Bundling tests 232
■
Covering all
the bases 235
7.2 Mocking OSGi 237
Testing expected behavior 237
■
Mocking in action 238
Mocking unexpected situations 240
■
Coping with multithreaded
tests 241
■
Exposing race conditions 243
7.3 Advanced OSGi testing 244
OSGi test tools 245
■
Running tests on multiple frameworks 246
Unit testing 250
■
Integration testing 251
■
Management
testing 254
7.4 Summary 257
8
Debugging applications 258
8.1 Debugging bundles 259
Debugging in action 261
■
Making things right with HotSwap 266
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CONTENTS
xi
8.2 Solving class-loading issues 271
ClassNotFoundException vs. NoClassDefFoundError 272
■
Casting
problems 274
■
Using uses constraints 275
■
Staying clear of
Class.forName() 278
■
Following the Thread Context Class
Loader 280
8.3 Tracking down memory leaks 283
Analyzing OSGi heap dumps 283
8.4 Dangling services 287
Finding a dangling service 287
■
Protecting against dangling
services 288
8.5 Summary 290
9
Managing bundles 292
9.1 Versioning packages and bundles 293
Meaningful versioning 293
■
Package versioning 295
Bundle versioning 297
9.2 Configuring bundles 299
Configuration Admin Service 299
■
Metatype Service 309
Preferences Service 312
9.3 Starting bundles lazily 314
Understanding activation policies 315
■
Using activation
policies 316
9.4 Summary 317
10
Managing applications 319
10.1 Deploying bundles 320
Introducing management agents 320
■
OSGi Bundle Repository 321
Deployment Admin 330
10.2 Ordering bundle activation 337
Introducing the Start Level Service 338
■
Using the Start Level
Service 339
10.3 Summary 342
PART 3 ADVANCED TOPICS 343
11
Component models and frameworks 345
11.1 Understanding component orientation 346
What are components? 346
■
Why do we want components? 348
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CONTENTS
xii
11.2 OSGi and components 349
OSGi’s service-oriented component model 349
■
Improving upon
OSGi’s component model 351
■
Painting with components 355
11.3 Declarative Services 355
Building Declarative Services components 356
■
Providing services
with Declarative Services 357
■
Consuming services with Declarative
Services 359
■
Declarative Services component lifecycle 364
11.4 Summary 371
12
Advanced component frameworks 373
12.1 Blueprint Container 374
Blueprint architecture 374
■
Providing services with Blueprint 375
Consuming services with Blueprint 378
■
Blueprint component
lifecycle 382
■
Advanced Blueprint features 387
12.2 Apache Felix iPOJO 391
Building iPOJO components 392
■
Providing services with iPOJO 393
Consuming services with iPOJO 395
■
iPOJO component
lifecycle 400
■
Instantiating components with iPOJO 404
12.3 Mix and match 408
12.4 Summary 411
13
Launching and embedding an OSGi framework 412
13.1 Standard launching and embedding 413
Framework API overview 413
■
Creating a framework
instance 415
■
Configuring a framework 417
■
Starting a
framework instance 419
■
Stopping a framework instance 420
13.2 Launching the framework 421
Determining which bundles to install 422
■
Shutting down
cleanly 422
■
Configuring, creating, and starting the framework 423
Installing the bundles 424
■
Starting the bundles 424
■
Starting the
main bundle 425
■
Waiting for shutdown 426
13.3 Embedding the framework 427
Inside vs. outside 427
■
Who’s in control? 431
■
Embedded
framework example 432
13.4 Summary 437
14
Securing your applications 438
14.1 To secure or not to secure 439
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[...]... bundles, including how to define bundle metadata, package your bundle content, and add lifecycle support We also describe how to go about dividing an application into bundles, demonstrating techniques on an existing open source project Chapter 7 shows how to test bundles and OSGi- based applications We look into running your existing tests in OSGi and mocking OSGi APIs In addition to unit and integration... our OSGi discussion is in the following chapters We also look at the state of modularity support in Java as well as in some related technologies Chapter 2 explores the module layer of the OSGi framework We start with a general discussion of modularity in computing and then continue by describing OSGi s module concept, called a bundle We present OSGi s declarative metadata-based approach for creating. .. at launching the OSGi framework We describe the standard approach for configuring and creating OSGi frameworks We also show how you can use the standard API to embed an OSGi framework into an existing application Chapter 14 delves into operating OSGi in a secure environment We describe the issues involved and approaches to alleviating them We explain how OSGi extends the standard Java security architecture... public interface in one package, a private implementation in another, and a main class in yet another Listing 1.1 Example of the limitations of Java s object-orientated encapsulation Greeting .java package org.foo.hello; public interface Greeting { void sayHello(); } B package org.foo.hello.impl; import org.foo.hello.Greeting; www.it-ebooks.info Simple interface GreetingImpl .java 6 CHAPTER 1 OSGi revealed... class GreetingImpl implements Greeting { final String m_name; C public GreetingImpl(String name) { m_name = name; } Interface implementation public void sayHello() { System.out.println("Hello, " + m_name + "!"); } } Main .java package org.foo.hello.main; import org.foo.hello.Greeting; import org.foo.hello.impl.GreetingImpl; public class Main { public static void main(String[] args) { Greeting greet =... OSGi technology www.it-ebooks.info www.it-ebooks.info OSGi revealed This chapter covers ■ Understanding Java s built -in support for modularity ■ Introducing OSGi technology and how it improves Java modularity ■ Positioning OSGi with respect to other technologies The Java platform is an unqualified success story It’s used to develop applications for everything from small mobile devices to massive enterprise... lack of modularization in Java These include the following: ■ ■ ■ Programming practices to capture logical structure Tricks with multiple class loaders Serialization between in- process components 3 www.it-ebooks.info www.it-ebooks.info 5 The what and why of OSGi improve maintainability by enforcing the logical module boundaries; we’ll discuss more modularity details in chapter 2 The notion of modularity... naturally into three parts: 1 2 3 Explaining the core OSGi specification Describing how to work with the specification in practice Introducing advanced OSGi- related topics xx www.it-ebooks.info ABOUT THIS BOOK xxi In part 1 of the book, we focus on explaining the most common aspects of the OSGi core specification from the user’s perspective We introduce OSGi according to its three-layer architecture:... been designing and building OSGi applications since 2005 in many different areas including build tools, component models, data persistence, desktop UIs, management, messaging, provisioning, resolvers, and RPC He contributes to the Apache Felix project especially in the area of development tooling via the Sigil subproject He is also directly involved in developing specifications for the OSGi Alliance... presenting command or shell interaction, normal Courier typeface is used to indicate program output, while bold is used to indicate user input Code annotations accompany many of the listings, highlighting important concepts In some cases, numbered bullets link to explanations that follow the listing Author Online Purchase of OSGi in Action includes free access to a private web forum run by Manning Publications .
Testing applications 230
7.1 Migrating tests to OSGi 231
In- container testing 231
■
Bundling tests 232
■
Covering all
the bases 235
7.2 Mocking OSGi. We look into
running your existing tests in OSGi and mocking OSGi APIs. In addition to unit and
integration testing, we discuss management testing and
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