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AOP and IoC |
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The subelement <value> sets the ‘name’
property by calling the set method as
setName(“amit”); This process is called
setter injection.
constructor injection
: For constructor injection, we use constructor with parameters
as shown below:
public class nameBean {
String name;
public nameBean (String a) {
name = a;
}}
We will set the property ‘name’ while creating
an instance of the bean ‘nameBean’ as
nameBean bean1 = new nameBean(“amit”);
Here we use the <constructor-arg> element to
set the the property by constructor injection
as:
<bean id=”bean1" class=”nameBean “>
<constructor-arg>
<value>Bean Value</value>
</constructor-arg>
</bean>
To set properties that reference other beans
<ref>, subelement of <property> is used as
shown below:
<bean id=”bean1" class=”bean11">
<property name=”game”>
<ref bean=”bean2"/>
</property>
</bean>
<bean id=”bean2" class=”bean22" />
The IOC containers
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 |
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that help to assemble components fromdifferent 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.
Let’s see how Spring container implements the
IoC concepts
Spring should not, however, be confused with
traditional heavyweight EJB containers, which
are often large. The Spring actually comes with
two distinct containers:
1. Bean Factories - defined by “ o r g . s p r i
n g f r a m e w o r k beans.factory.BeanFactory” are the
simplest containers, providing support for dependency
injection.
2. Application contexts - defined by “org.springframework.context.
ApplicationContext” provides the application
framework services.
Configuration metadata
As can be seen in the above image, the Spring
IoC container consumes some form of configuration metadata; this
configuration metadata is nothing more than how you
(as an application developer) inform the Spring
container as to how to “instantiate, configure,
and assemble [the objects in your application]”.
This configuration metadata is typically supplied
in a simple and intuitive XML format. When
using XML-based configuration metadata, you
write bean definitions for those beans that you
want the Spring IoC container to manage, and
then let the container do it’s stuff.
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
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Nov 2007 | Java Jazz Up | 8 |
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