AspectJ in Action: Practical Aspect-Oriented Programming

A software system is the realization of a set of concerns. One of the central premises of object-oriented programming is that each concern should be implemented as a separate module. However, there are certain system-wide concerns, such as logging, security, performance, and so forth, that often need to be addressed in many, if not all of the modules. Consequently, the code to handle these system-wide concerns may be mixed in with the core logic of a huge number of modules, resulting in lower productivity, poor quality, and systems that are hard to evolve.

Aspect-oriented programming overcomes these problems by modularizing the system-wide concerns.

AspectJ enables AOP programming in Java by adding a few new language constructs. By using Java as the base language and creating a final system that is compatible with Java byte code specification, AspectJ passes on all the benefits of Java. The use of Java as the base language also makes AspectJ a relatively easy language to learn.

AspectJ in Action is a practical guide to AOP and AspectJ. The reusable code examples that are provided will enable quick implementation of functionality in your system.

The book is divided into three parts. The first part introduces AOP and AspectJ and will be helpful to developers wanting to learn or advance their knowledge of AspectJ. The second and third parts present examples of everyday situations in which you can use simple and easy AspectJ solutions to implement common system requirements such as logging, policy enforcement, resource pooling, business rules, thread-safety, authentication and authorization, as well as transaction management.

What's inside:

• In-depth coverage of AOP and AspectJ
• Design patterns and idioms
• Solutions to real-world problems
• Much reusable code content
• AspectJ version 1.1

Table of Contents

preface xvii
how real is AspectJ? xix
into the future! xxi
acknowledgments xxiii
about this book xxv

Part 1  Understanding AOP and AspectJ   1

1  Introduction to AOP   3

1.1 The architect’s dilemma 5

1.2 Evolution of programming methodologies 6

1.3 Managing system concerns 7

Identifying system concerns 8

A one-dimensional solution 10

It’s all about modularizing 11

1.4 Implementing crosscutting concerns in nonmodularized systems 14

Symptoms of nonmodularization 15

Implications of nonmodularization 18

Introducing AOP 19

A bit of history 20

The AOP methodology 21

1.5 Anatomy of an AOP language 22

The AOP language specification 23

The AOP language implementation 24

A weaving example 26

1.6 Benefits of AOP 27

1.7 Myths and realities of AOP 29

1.8 Summary 30

2  Introducing AspectJ   32

2.1 AspectJ: a bird’s eye view 33

Crosscutting in AspectJ 33

Crosscutting elements 34

2.2 AspectJ Hello World 37

2.3 AspectJ: under the hood 40

2.4 The join point model 43

Exposed join point categories 44

Join point demonstration example 50

2.5 Aspects 55

2.6 AspectJ logistics overview 59

The AspectJ compiler 59

AspectJ browser 60

IDE integration 61

2.7 Summary 62

3  AspectJ: syntax basics   64

3.1 Pointcuts 65

Wildcards and pointcut operators 67

Signature syntax 68

Implementing pointcuts 73

3.2 Advice 81

Anatomy of advice 82

The before advice 83

The after advice 83

The around advice 85

Comparing advice with methods 86

Passing context from a join point to advice 87

Returning a value from around advice 89

An example using around advice: failure handling 90

Context collection example: caching 92

3.3 Static crosscutting 95

Member introduction 95

Modifying the class hierarchy 96

Introducing compile-time errors and warning 97

3.4 Tips and tricks 98

3.5 Summary 99

4  Advanced AspectJ   100

4.1 Accessing join point information via reflection 101

The reflective API 103

Using reflective APIs 106

4.2 Aspect precedence 111

Ordering of advice 114

Explicit aspect precedence 115

Aspect inheritance and precedence 117

Ordering of advice in a single aspect 119

Aspect precedence and member introduction 120

4.3 Aspect association 122

Default association 123

Per-object association 125

Per-control-flow association 128

Implicit limiting of join points 132

Comparing object association with member introduction 134

Accessing aspect instances 135

4.4 Exception softening 136

4.5 Privileged aspects 139

4.6 Summary 141

Part 2  Basic applications of AspectJ   143

5  Monitoring techniques: logging, tracing, and profiling   145

5.1 Why use AspectJ for logging? 146

A simple case in point 147

Logging the conventional way 149

Logging the aspect-oriented way 153

5.2 What’s wrong with conventional logging 154

5.3 The beauty of AspectJ-based logging 156

5.4 Developing logging and tracing aspects 156

Method call tracing 157

Exceptions logging 163

5.5 Common logging idioms 167

Logging the method parameters 168

Indenting the log statements 170

Aspect precedence 172

Changing the underlying logging mechanism 173

Using logging in a multithreaded environment 173

5.6 Extending logging for other usage 174

Testing 174

Profiling 175

5.7 Summary 176

6  Policy enforcement: system wide contracts   178

6.1 AspectJ-based policy enforcement overview 179

6.2 The current solution and its challenges 181

6.3 Enforcement using AspectJ 182

Policy enforcement implementation choices 183

The role of policy enforcement during the product lifecycle 184

6.4 Policy enforcement patterns 185

Detecting the violation of a specific call pattern 185

Implementing flexible access control 187

Enforcing the best-practices principles 189

6.5 Example: implementing EJB programming restrictions 191

Implementing "no AWT" 193

Implementing "no nonfinal static field access" 194

6.6 Example: implementing Swing policies 195

Understanding the problem 196

Detecting the violation 198

6.7 Summary 200

7  Optimization: pooling and caching   202

7.1 The typical case 203

Return, reuse, recycle: The role of resource pooling 205

Resource pooling issues 206

7.2 Diving into the pool using AspectJ 208

Designing a template aspect 208

Implementing the template aspect 209

7.3 Example 1: database connection pooling 211

Understanding the database connection pool interface 212

AspectJ-based database connection pooling 213

Implementing the connection pool 216

Testing our solution 218

Tweaking the solution 222

7.4 Example 2: thread pooling 223

The echo server 224

Understanding the thread pool interface 226

AspectJ-based thread pooling 226

Implementing the thread pool 230

Testing our solution 231

Tweaking the solution 234

7.5 Extending pooling concepts to caching 235

AspectJ-based caching: the first version 237

AspectJ-based caching: the second version 239

Ideas for further improvements 240

7.6 Summary 241

Part 3  Advanced applications of AspectJ   243

8  Design patterns and idioms   245

8.1 The worker object creation pattern 247

The current solution 248

An overview of the worker object creation pattern 249

The pattern template 249

A summary of the worker object creation pattern 256

8.2 The wormhole pattern 256

The current solution 257

An overview of the wormhole pattern 257

The pattern template 258

A summary of the wormhole pattern 260

8.3 The exception introduction pattern 260

The current solution 261

An overview of the exception introduction pattern 265

The pattern template 265

A summary of the exception introduction pattern 269

8.4 The participant pattern 270

Current solutions 271

An overview of the participant pattern 273

The pattern template 274

A summary of the participant pattern 276

8.5 Idioms 277

Avoiding infinite recursion 277

Nullifying advice 279

Providing empty pointcut definitions 280

Providing a default interface implementation 281

8.6 Summary 285

9  Implementing thread safety   286

9.1 Swing’s single-thread rule 287

The rule 288

The problem 288

The solution 289

9.2 A test problem 290

9.3 Solution: the conventional way 293

9.4 Solution: the AspectJ way 297

The first version 298

The second version 303

The third version 307

9.5 Improving the solution 311

Dealing with exceptions 311

Avoiding the overhead 312

9.6 Improving the responsiveness of UI applications 313

9.7 Modularizing the read-write lock pattern 316

Implementation: the conventional way 316

Implementation: the AspectJ way 318

9.8 Summary 321

10  Authentication and authorization   323

10.1 Problem overview 324

10.2 A simple banking example 325

10.3 Authentication: the conventional way 329

Implementing the solution 329

Testing the solution 331

10.4 Authentication: the AspectJ way 333

Developing the solution 333

Testing the solution 336

10.5 Authorization: the conventional way 336

Understanding JAAS-based authorization 337

Developing the solution 338

Testing the solution 342

Issues with the conventional solution 345

10.6 Authorization: the AspectJ way 346

Developing the solution 346

Testing the solution 350

10.7 Fine-tuning the solution 353

Using multiple subaspects 353

Separating authentication and authorization 354

10.8 Summary 354

11  Transaction management   356

11.1 Example: a banking system with persistence 358

Implementing the core concern 358

Setting up the test scenario 362

11.2 The conventional solution 364

Using the same connection object 365

Committing at the top level only 367

11.3 Developing a simple AspectJ-based solution 368

Implementing the JDBC transaction aspect 368

Handling legacy system issues 373

Enabling transaction management for the banking system 374

Testing the solution 375

11.4 Improving the solution 378

Using the participant pattern 379

Implementing the JDBC transaction aspect: the second version 382

Testing the solution 385

11.5 Using AspectJ with advanced transaction-management systems 387

11.6 Summary 390

12  Implementing business rules   391

12.1 Using business rules in enterprise applications 392

12.2 An overview of business rule implementation 393

12.3 Current mechanisms 393

12.4 Introducing a solution using AspectJ 394

The template 394

12.5 Example: the banking system 396

Implementing the core business logic 396

Implementing the first business rule 401

Implementing the second business rule 403

Writing a test program 406

12.6 Implementing business rules with a rule engine 411

An overview of the rule engine 412

Using a rule engine 412

Modularizing with AspectJ 415

12.7 Example: a banking system with a rule engine 417

A brief overview of Jess (Java Expert System Shell) 417

Specifying rules 418

Understanding the rule invocation aspect 420

12.8 Summary 423

13  The next step   425

13.1 Applying AspectJ to new problems 426

Talking the talk 426

Walking the walk 427

13.2 Employing AspectJ in development phases 427

AspectJ in the design phase 428

AspectJ in the implementation phase 428

AspectJ in the testing phase 431

AspectJ in the maintenance phase 432

AspectJ in legacy projects 432

13.3 A word of warning 433

13.4 Evangelizing AspectJ 434

13.5 Parting thoughts 436

A  The AspectJ compiler   438

A.1 Downloading and setting up 439

A.2 An overview of the compiler 440

A.3 Compiling source files 441

A.4 Compiling source directories 441

A.5 Weaving into JAR files 442

A.6 Creating aspect libraries 443

A.7 Using aspect libraries 444

A.8 Utilizing incremental compilation mode 444

A.9 Producing useful warnings 446

B  Understanding Ant integration   447

B.1 Compiling source files using an Ant task 448

B.2 Weaving into JAR files using an Ant task 451

B.3 Creating aspect libraries using an Ant task 452

B.4 Utilizing aspect libraries using an Ant task 453

B.4 Utilizing incremental compilation using an Ant task 453

resources 455
index 461

一個軟體系統是一組關注點的實現。面向對象編程的核心原則之一是每個關注點應該作為一個獨立的模塊來實現。然而，有一些系統級的關注點，例如日誌記錄、安全性、性能等，通常需要在許多模塊中或者幾乎所有模塊中進行處理。因此，處理這些系統級關注點的代碼可能與大量模塊的核心邏輯混合在一起，導致生產力降低、質量差和難以演進的系統。

面向方面的編程通過將系統級關注點模塊化來解決這些問題。

AspectJ通過添加一些新的語言結構，使Java能夠進行面向方面的編程。通過使用Java作為基礎語言並創建與Java字節碼規範兼容的最終系統，AspectJ繼承了Java的所有優點。使用Java作為基礎語言也使得AspectJ相對容易學習。

《AspectJ實戰》是一本關於面向方面編程和AspectJ的實用指南。提供的可重用代碼示例將使您能夠快速在系統中實現功能。

該書分為三個部分。第一部分介紹了面向方面編程和AspectJ，對於想要學習或提升對AspectJ知識的開發人員非常有幫助。第二部分和第三部分介紹了日常情況下可以使用簡單易用的AspectJ解決方案來實現常見系統需求，例如日誌記錄、策略執行、資源池、業務規則、線程安全、身份驗證和授權以及事務管理。

內容包括：
- 深入介紹面向方面編程和AspectJ
- 設計模式和習慣用法
- 解決現實世界問題的解決方案
- 大量可重用代碼內容
- AspectJ版本1.1

目錄：
- 前言
- 第一部分：理解AOP和AspectJ
- 第二部分：介紹AspectJ
- 第三部分：使用AspectJ解決常見系統需求

以上是《AspectJ實戰》的翻譯。