深入理解Spring Dynamic Modules

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"Spring Dynamic Modules in Action 是一本由 Arnaud Cogoluegnes、Thierry Templier 和 Andy Piper 合著的专业书籍，由 Manning 出版社出版。这本书深入探讨了如何在 Java Spring 框架中有效地利用动态模块来构建可扩展和灵活的应用程序。" 在 Spring 框架中，Spring Dynamic Modules 提供了一种方法来处理不同运行时环境（如 OSGi、JMX 等）的动态性，使得开发者能够构建模块化、可配置且适应性强的应用程序。通过使用 Spring Dynamic Modules，你可以创建能够感知并适应运行时环境变化的组件，这在大型分布式系统和企业级应用中尤其有价值。书中可能涵盖了以下关键知识点： 1. **OSGi**：Open Service Gateway Initiative，一个用于创建模块化软件的开放标准。Spring Dynamic Modules 使得 Spring 应用能无缝地工作在 OSGi 容器（如 Felix、Equinox）中，支持服务的热更新和依赖管理。 2. **动态上下文感知**：Spring Dynamic Modules 提供了 API 和注解，让开发者能够编写能够感知当前运行时环境（如安全策略、系统属性等）的bean。 3. **模块化设计**：通过模块化，可以将复杂的应用程序拆分为更小、更独立的部分，从而简化开发、测试和维护。书里可能介绍了如何使用 Spring DM 来定义和管理这些模块。 4. **配置管理**：Spring 的核心是依赖注入，Spring Dynamic Modules 进一步扩展了这一概念，允许根据运行时环境动态地调整配置。 5. **安全性集成**：在多模块环境中，安全性是至关重要的。书可能讨论了如何使用 Spring DM 配合现有的安全框架（如 Spring Security）来实现细粒度的权限控制。 6. **部署与管理**：讲解如何在不同的运行时环境中部署和管理 Spring 应用，包括监控、日志记录和故障排查等最佳实践。 7. **案例研究**：作者可能提供了实际的案例，展示了如何在真实项目中使用 Spring Dynamic Modules 解决问题，提升系统的灵活性和可维护性。通过阅读《Spring Dynamic Modules in Action》，开发者不仅可以学习到如何使用 Spring 框架来构建模块化系统，还能了解到如何应对复杂的企业级挑战，如服务发现、版本管理和系统升级等。这本书对于想要深入了解 Spring 模块化开发的 Java 开发者来说是一份宝贵的资源。

foreword

It must have been in 2006 that I got a call as OSGi’s Technical Director from Adrian

Colyer, CTO of Interface21, the company that was the source of the Spring Frame-

work. Yes, I’d heard of the Spring Framework, and I understood that it was a great

improvement over existing techniques for writing software for the enterprise. As a

developer who had gained most of his experience in developing embedded and mid-

dleware applications, I found all that XML rather foreign. However, I’d noticed the

enterprise world’s interest in OSGi, so I too was interested.

It turned out that Interface 21, BEA, and Oracle were considering creating support

for OSGi in the Spring Framework. Spring is very good at configuring an application

built out of simple objects that use, among other things, the simplified Spring inter-

faces to communicate with the world. However, Spring did not provide any support

for modularity. In contrast, OSGi provides strong modularity support but it’s not

strong in configuration and it had no services in the enterprise space. This was a

match made in heaven!

To discuss supporting OSGi in Spring, Adrian proposed a conference call with Hal

Hildebrand (Oracle), John Wells (BEA), and one of the authors of this book: Andy

Piper (BEA). B.J. Hargrave (IBM) also attended as OSGi’s CTO. The initial conference

call was followed by a meeting in London at the offices of BEA. It was a meeting I’ll

always remember, it was the start of what became Spring DM. At first, I felt that the

group saw OSGi as something that needed to be supported by Spring; that is, as one of

many things to be supported. As the meeting progressed, it became clear how nice the

combination of Spring and OSGi could be; there was a lot of synergy and surprisingly

little overlap. At the end of the meeting, we were thrilled with this project's potential.

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FOREWORD

xvi

The Spring DM project became crucial for the adoption of OSGi in the enterprise

space. At that time, OSGi had been adopted by Eclipse, which made it acceptable for

general programming. However, the enterprise space is conservative and was hesitant

about adopting OSGi. The fact that Interface21 people started to sell OSGi at the many

conferences they visited helped to give OSGi a place in the enterprise world. That said,

it was a surprise for me when Interface21 changed their name to SpringSource and

put a lot of emphasis on the OSGi connection. They quickly became a member of the

OSGi Alliance and started RFC 124, as an endeavor to put Spring DM under the OSGi

flag. This RFC later turned into the Blueprint specification. SpringSource also intro-

duced the dm Server (now project Gemini in Eclipse) and more importantly, they

launched the OSGi Bundle Repository, filling a crucial gap for the acceptance of OSGi

in the enterprise. This repository contained bundles based on open source projects.

Before this repository, developers were forced to create their own bundles from open

source projects, and this was not always painless.

Alas, it still is not always painless. The core principle of OSGi is modularity, creat-

ing inside and outside spaces with well-defined ports. The advantages of modularity

are numerous and well proven. However, OSGi enforces those rules strictly on all lev-

els. Unfortunately, it turns out that many open source libraries do not live well inside

modules—thay need global visibility of all classes. Over the past decade, mainstream

Java has given rise to a number of patterns that appear to be modular but are not so

in reality.

That’s why this book about Spring DM and Blueprint is so crucial. First, it provides

an excellent introduction to OSGi and what the guiding principles are. As one of the

participants of the OSGi specification, I do not think I could have improved on this

description. The book then explains how you should structure your projects with

Spring DM, but it doesn’t stop there. It doesn’t hide the complexities of today’s reality,

which is that you have to use existing (open source) libraries. It provides an extensive

description of what you should do when you need to use libraries that do not play well

in a modular world.

If you’re already building applications using Spring, then read this book and take

the leap into the OSGi world. Although you might run into some hurdles, this book

will help you solve them, and the rewards are well worth it.

PETER KRIENS

OSGI TECHNICAL DIRECTOR

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PREFACE

xviii

change you made had unforeseen consequences that could only be discovered

by running the full QA suite—a process that takes 48 hours.

■

The build-the-world problem Your development team is in Beijing, Mumbai, and

San Ramon, and each subteam works on different parts of the application in dif-

ferent time zones and on different development schedules. As the team and appli-

cation grow, you find that it becomes increasingly hard to keep the different parts

of the product separate—any time you make a change, you find it impossible to

tell which teams will be affected by your changes. The only solution is to keep all

the teams on exactly the same version of the application, and to rebuild and retest

the entire product every time any change is made. You eventually spend all of your

time building and testing the product and none actually developing it. The com-

pany goes bankrupt, you lose your job, and now you have plenty of time to watch

soccer—if only your widescreen TV hadn’t been repossessed.

These problems are all symptoms of unmodular applications.

As authors, we come from different but related, backgrounds. Arnaud and Thierry

come from the enterprise application development sphere, and Andy comes from a

middleware product development background, thanks to his jobs at BEA and then Ora-

cle. But we all share the same enthusiasm and passion for Spring technologies and for

anything that can help us build better software. Arnaud remembers his first contact

with Spring Dynamic Modules—he attended Costin Leau’s (Spring Dynamic Modules’

project lead) talk at SpringOne Europe in 2008. What could be more exciting for a

Spring enthusiast than to be able to use Spring on the OSGi platform? At last, real, run-

time modularity meets Spring! Unfortunately, there was not, at the time, much in the

way of resources around Spring Dynamic Modules. That was when he met Thierry and

they both went on to write a French book on Spring. In contrast, Andy in 2008 had

already been working with Spring Dynamic Modules for a couple of years, having been

involved with its original development and having used it extensively on several BEA

products. It was later in 2009 that Manning Publications contacted Arnaud and Thierry

to suggest writing a proposal for a Spring Dynamic Modules in Action book.

Working with Manning can be difficult: they have high standards for their books,

and we had no idea how high the mountain would turn out to be when we wrote that

proposal, which then passed a succession of reviews. Some reviewers were happy with

it, but others were tough, like that Oracle guy, Andy Piper. But his remarks were con-

structive, and based on his feedback Manning suggested that he be involved in the

writing process. After all, if you want something done right, you do it yourself! Having

a native English speaker on the writing team also proved useful, as some say that the

French accent comes across even in written text.

We have done our best to make this book as comprehensive and accessible as pos-

sible. We hope you’ll benefit from our experience with the Spring Framework, OSGi,

and in making both worlds cohabit as harmoniously as possible using Spring DM. We

believe that these technologies are an important piece of the puzzle in bringing your

applications closer to the mythical “perfect” program.

Download from Wow! eBook <www.wowebook.com>

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