附录 1 外文原文
Introducing the Spring Framework
The Spring Framework: a popular open source application framework that
addresses many of the issues outlined in this book. This chapter will introduce the
basic ideas of Spring and dis-cuss the central “bean factory” lightweight Inversion-of-
Control (IoC) container in detail.
Spring makes it particularly easy to implement lightweight, yet extensible, J2EE
archi-tectures. It provides an out-of-the-box implementation of the fundamental
architectural building blocks we recommend. Spring provides a consistent way of
structuring your applications, and provides numerous middle tier features that can
make J2EE development significantly easier and more flexible than in traditional
The basic motivations for Spring are:
To address areas not well served by other frameworks. There are numerous good
solutions to specific areas of J2EE infrastructure: web frameworks, persistence
solutions, remoting tools, and so on. However, integrating these tools into a
comprehensive architecture can involve significant effort, and can become a burden.
Spring aims to provide an end-to-end solution, integrating spe-cialized frameworks
into a coherent overall infrastructure. Spring also addresses some areas that other
frameworks don’t. For example, few frameworks address generic transaction
management, data access object implementation, and gluing all those things together
into an application, while still allowing for best-of-breed choice in each area. Hence
we term Spring an application framework, rather than a web framework, IoC or AOP
framework, or even middle tier framework.
To allow for easy adoption. A framework should be cleanly layered, allowing the
use of indi-vidual features without imposing a whole world view on the application.
Many Spring features, such as the JDBC abstraction layer or Hibernate integration,
can be used in a library style or as part of the Spring end-to-end solution.
To deliver ease of use. As we’ve noted, J2EE out of the box is relatively hard to
use to solve many common problems. A good infrastructure framework should make
simple tasks simple to achieve, without forcing tradeoffs for future complex
requirements (like distributed transactions) on the application developer. It should
allow developers to leverage J2EE services such as JTA where appropriate, but to
avoid dependence on them in cases when they are unnecessarily complex.
To make it easier to apply best practices. Spring aims to reduce the cost of
adhering to best practices such as programming to interfaces, rather than classes,
almost to zero. However, it leaves the choice of architectural style to the developer.
Non-invasiveness. Application objects should have minimal dependence on the
framework. If leveraging a specific Spring feature, an object should depend only on
that particular feature, whether by implementing a callback interface or using the
framework as a class library. IoC and AOP are the key enabling technologies for
avoiding framework dependence.
Consistent configuration. A good infrastructure framework should keep
application configuration flexible and consistent, avoiding the need for custom
singletons and factories. A single style should be applicable to all configuration needs,
from the middle tier to web controllers.
Ease of testing. Testing either whole applications or individual application
classes in unit tests should be as easy as possible. Replacing resources or application
objects with mock objects should be straightforward.
To allow for extensibility. Because Spring is itself based on interfaces, rather
than classes, it is easy to extend or customize it. Many Spring components use
strategy interfaces, allowing easy customization.
A Layered Application Framework
Chapter 6 introduced the Spring Framework as a lightweight container,
competing with IoC containers such as PicoContainer. While the Spring lightweight
container for JavaBeans is a core concept, this is just the foundation for a solution for
all middleware layers.
Basic Building Blocks
pring is a full-featured application framework that can be leveraged at many
levels. It consists of multi-ple sub-frameworks that are fairly independent but still
integrate closely into a one-stop shop, if desired. The key areas are:
Bean factory. The Spring lightweight IoC container, capable of configuring and
wiring up Java-Beans and most plain Java objects, removing the need for custom
singletons and ad hoc configura-tion. Various out-of-the-box implementations include
an XML-based bean factory. The lightweight IoC container and its Dependency
Injection capabilities will be the main focus of this chapter.
Application context. A Spring application context extends the bean factory
concept by adding support for message sources and resource loading, and providing
hooks into existing environ-ments. Various out-of-the-box implementations include
standalone application contexts and an XML-based web application context.
AOP framework. The Spring AOP framework provides AOP support for method
interception on any class managed by a Spring lightweight container. It supports easy
proxying of beans in a bean factory, seamlessly weaving in interceptors and other
advice at runtime. Chapter 8 dis-cusses the Spring AOP framework in detail. The
main use of the Spring AOP framework is to provide declarative enterprise services
Auto-proxying. Spring provides a higher level of abstraction over the AOP
framework and low-level services, which offers similar ease-of-use to .NET within a
J2EE context. In particular, the provision of declarative enterprise services can be
driven by source-level metadata.
Transaction management. Spring provides a generic transaction management
infrastructure, with pluggable transaction strategies (such as JTA and JDBC) and
various means for demarcat-ing transactions in applications. Chapter 9 discusses its
rationale and the power and flexibility that it offers.
JDBC support. Spring offers two levels of JDBC abstraction that significantly
ease the effort of writing JDBC-based DAOs: the org.springframework.jdbc.core
package (a template/
callback approach) and the org.springframework.jdbc.object package (modeling
RDBMS operations as reusable objects). Using the Spring JDBC packages can deliver
much greater pro-ductivity and eliminate the potential for common errors such as
leaked connections, compared with direct use of JDBC. The Spring JDBC abstraction
integrates with the transaction and DAO abstractions.
Integration with O/R mapping tools. Spring provides support classes for O/R
Mapping tools like Hibernate, JDO, and iBATIS Database Layer to simplify resource
setup, acquisition, and release, and to integrate with the overall transaction and DAO
abstractions. These integration packages allow applications to dispense with custom
ThreadLocal sessions and native transac-tion handling, regardless of the underlying
O/R mapping approach they work with.
Web MVC framework. Spring provides a clean implementation of web MVC,
consistent with the JavaBean configuration approach. The Spring web framework
enables web controllers to be configured within an IoC container, eliminating the need
to write any custom code to access business layer services. It provides a generic
DispatcherServlet and out-of-the-box controller classes for command and form
handling. Request-to-controller mapping, view resolution, locale resolution and other
important services are all pluggable, making the framework highly extensi-ble. The
web framework is designed to work not only with JSP, but with any view technology,
such as Velocity—without the need for additional bridges. Chapter 13 discusses web
tier design and the Spring web MVC framework in detail.
Remoting support. Spring provides a thin abstraction layer for accessing remote
services without hard-coded lookups, and for exposing Spring-managed application
beans as remote services. Out-of-the-box support is included for RMI, Caucho’s
Hessian and Burlap web service protocols, and WSDL Web Services via JAX-RPC.
Chapter 11 discusses lightweight remoting.
While Spring addresses areas as diverse as transaction management and web
MVC, it uses a consistent approach everywhere. Once you have learned the basic
configuration style, you will be able to apply it in many areas. Resources, middle tier
objects, and web components are all set up using the same bean configuration
mechanism. You can combine your entire configuration in one single bean definition
file or split it by application modules or layers; the choice is up to you as the
application developer. There is no need for diverse configuration files in a variety of
formats, spread out across the application.
Spring on J2EE
Although many parts of Spring can be used in any kind of Java environment, it is
primarily a J2EE application framework. For example, there are convenience classes
for linking JNDI resources into a bean factory, such as JDBC DataSources and EJBs,
and integration with JTA for distributed transaction management. In most cases,
application objects do not need to work with J2EE APIs directly, improving
reusability and meaning that there is no need to write verbose, hard-to-test, JNDI
Thus Spring allows application code to seamlessly integrate into a J2EE
environment without being unnecessarily tied to it. You can build upon J2EE services
where it makes sense for your application, and choose lighter-weight solutions if there
are no complex requirements. For example, you need to use JTA as transaction
strategy only if you face distributed transaction requirements. For a single database,
there are alternative strategies that do not depend on a J2EE container. Switching
between those transac-tion strategies is merely a matter of configuration; Spring’s
consistent abstraction avoids any need to change application code.
Spring offers support for accessing EJBs. This is an important feature (and
relevant even in a book on “J2EE without EJB”) because the use of dynamic proxies
as codeless client-side business delegates means that Spring can make using a local
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