模块化Java：OSGi与Spring打造灵活应用实战指南

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《模块化Java：利用OSGi和Spring构建灵活应用》（9781934356401-1934356409）是一本由 Craig Walls 所著的专业技术书籍，专为 Larry Cormier 预备，旨在帮助开发者理解和掌握模块化编程在企业级应用和移动应用开发中的关键作用。这本书获得了读者的高度评价。作者 Craig Walls 凭借其深厚的理论基础和实践经验，以易于理解的方式深入讲解了如何通过OSGi (服务组件框架) 和 Spring (轻量级的Java框架) 来实现模块化的Java应用程序设计。他不仅解释了模块化的重要性，还提供了丰富的实践指导，使读者仿佛置身于一个实际的OSGi工作坊中，亲自动手操作工具并见证成果。 Dr. Venkat Subramaniam，一位获奖的敏捷开发者创始人，赞扬这本书写作风格清晰，内容既专业又有趣。他提到这是一本无可挑剔的资源，对想要提升模块化Java技能的开发者来说非常有价值。 Frederic Daoud，作为《条纹与Java Web开发的乐趣》一书的作者，表示 Craig 在书中成功地阐述了模块化Java web应用开发的“为什么”和“如何”，特别是在结合OSGi后所展现的威力和优雅。 Erik Weibust，作为一名高级架构师，强调了这本书如何消除了人们对OSGi复杂性的误解，并展示了如何利用Spring来构建功能强大且符合企业级标准的Java应用。他肯定了 Craig 的做法，使得原本看似复杂的OSGi和Spring变得更加易于入门。《模块化Java：利用OSGi和Spring创建灵活应用》是一本实用且富有深度的指南，对于Java开发者尤其是希望提升应用灵活性、模块化设计能力的开发者来说，无论是企业级项目还是移动应用开发，都是不可或缺的学习资料。通过阅读本书，读者不仅能掌握核心概念，还能提升实际操作技巧，从而提升项目开发效率和应用质量。

INTRODUCING OSGI 15

Keep an Eye Out for OSGi 4.2

As I write this, version 4.1 is the latest release of the OSGi spec-

iﬁcation. But version 4.2 is in the works and should be ﬁnal very

soon. There’s some good stuff in there, such as distributed OSGi,

a common command shell, and a new declarative service

model based on Spring Dynamic Modules.

So, although JAR ﬁles may give the appearance of supporting modular-

ity, their weak boundaries fail to restrict access to their internal imple-

mentation. This leaves them vulnerable to misuse and tight coupling

between JAR ﬁles.

What’s needed is a way to fortif y the boundaries of a JAR ﬁle such that

outsiders can see and use only the published API of the library. It just

so happens that is where OSGi steps in.

1.3 Introducing OSGi

OSGi is a component framework speciﬁcation that 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 min i mal or no impact to the other modules.

Let’s take a look at the i ngredients that make up the OSGi 4.1 speci-

ﬁcation 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 a

bundle. Rather than create a completely new deployment mechanism,

OSGi leverages the existing JAR ﬁle format for bundles. OSGi bundles

are much li ke common JAR ﬁles, except that their META-INF/MANIFEST.MF

Report erratum

this copy is (P1.0 printing, May 2009)

Prepared exclusively for Larry Cormier

ROAD MAP 19

Dynamic Modularity

Another consequence of isolating bundles in their own class space is

that any given bundle may be installed, stopped, st arted, updated, or

uninstalled independently of other bundles in the framework. Among

other things, this makes it possible to sw ap out a bundle wit h a newer

version of the same bundle wh i l e the application continues to run.

Strong-Naming

Unlike traditional JAR ﬁles that have no way to deﬁnitively identify

themselves, OSGi bundles are discretely identiﬁed by a name (known

as the bundle’s sy mb olic name) and version number in the bundle’s

manifest.

It sh ould 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 i s still up to you to ensure that

the modules you create follow good modular design. OSGi does, how-

ever, encourage modular programming practices by making it easy to

create well-deﬁned modules and, in some cases, making it more difﬁ-

cult not to do so.

1.4 Road M ap

We’ll take a progressive approach as we explore OSGi, starting with

OSGi f undamentals. In Chapter

2, Getting Started, on page 24, we’ll

kick the tires on OSGi by getti ng to know two of the most popular OSGi

framework implementations, Apache Felix and Eclipse Equinox. We’ll

also start developing a few simple OSGi bundles and see them in action

as we deploy them into the OSGi framework.

Chapter

3, Dude, Where’s My JAR?, on page 45 will set the stage for

the rest of the book by describing Dude, Where’s My JAR?, the example

application t hat we’ll build as we learn OSGi and Spring Dynamic Mod-

ules. In this chapter, we’ll cover the basic features of the application as

well as a high-level design overview of how OSGi will be used to develop

it. We’ll also get acquainted w i th an OSGi development kit called Pax

Construct.

In Chapter

4, Working with B undles, on page 59, we’ll get st arted on the

example application by building one of the bundles that will deﬁne the

2. htt p://wiki.ops4j.org/display/ops4j/Pax+Construct

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Prepared exclusively for Larry Cormier

剩余245页未读，继续阅读

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