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<bean id=”bean1" class=”bean11">
<property name=”game”>
<ref bean=”bean2"/>
</property>
</bean>
<bean id=”bean2" class=”bean22" />
The IOC container
The mainstream JEE involves heavyweight containers
to develop applications. So exploring alternatives and
coming up with creative ideas have evolved a lot of open
source java communities. In the Java community there’s
been a rush of lightweight containers that help to assemble
components from different projects into a cohesive application. Several open source projects, including
Spring, PicoContainer, and HiveMind use the IoC pattern
to develop lightweight JEE Containers. The container
manages the life cycle and configuration of application
objects.
Spring should not, however, be confused with traditionally
heavyweight EJB containers, which are often
large. The Spring actually comes with two distinct containers:
Bean Factories-defined by “org.springframework. beans.
factory.BeanFactory” are the simplest containers, providing
support for dependency injection.
Application contexts - defined by “org.springframework.
context.Application Context” provides application framework
services.
BEAN FACTORY:
Bean factory is an implementation of the factory
design pattern. Its function is to create and dispense
beans. As the bean factory knows about many objects
within an application, it is able to create association
between collaborating objects as they are instantiated.
This emoves the burden of configuration from the bean
and the client.
BEAN FACTORY supports two object modes.
Singleton mode provides a shared instance of the
object with a particular name, which can be retrieved on
lookup. Singleton is the default and most often used
object mode. It is ideal for stateless service objects.
Prototype mode ensures that each retrieval will
result in the creation of an independent object. Prototype
mode would be best used in a case where each
user needed to have his or her own object.
The bean factory concept is the foundation of Spring
as an IOC container. IOC moves the responsibility for
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making things happen into the framework and away from
application code. The Spring framework uses JavaBean
properties and configuration data to figure out which
dependencies must be set.
There are several implementation of BeanFactory like
“org.springframework.beans.factory.xml.XmlBeanFactory”
which loads its beans based on the definition contained
in an XML file.
APPLICATION CONTEXT:
The Application Context is spring’s more advanced container.
Like ‘BeanFactory’ it can load bean definitions, wire beans
together and dispense beans upon request. Additonally, It also
provides:
1. A means for resolving text messages, including
support for internationalization ie. i18n
messages
2. A generic way to load file resources.
3.Events to notify beans that are registered as
listeners.
Because of additional functionality, ‘Application Context’
is preferred over a BeanFactory. BeanFactory is
used for simple applications and when the resource is
scarce like mobile devices.
III Service Abstraction Layers
Spring provides consistent integration with various
standard and 3rd party APIs through its various Service
abstraction layers. Few of them are:
1. Transaction Management abstraction for JTA, JDBC,
others
2. Data Access abstraction for JDBC, Hibernate,
JDO, TopLink, iBatis
3. Abstraction for Emailing
4. Remoting abstraction layers for EJB, Web
Services, RMI, Hessian/Burlap
Benefits of the Service Abstraction Layers in spring
framework:
1. There is no implicit contract with JNDI, etc.
2. It separates the user from the underlying
APIs.
3. It enhances the reusability to a great extent.
4. Spring abstractions always consist of inter
faces.
5. Testing is kept simpler than ever before.
6. For data access, Spring uses a generic
transaction infrastructure and DAO exception
hierarchy that is ommon across all sup
ported platforms. |
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July 2007 | Java Jazz Up |26 |
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| 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53 , Download PDF |
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