Spring 3.0 dependancy injection

Dependency Injection

rgupta.trainer@gmail.com

Dependency Injection
• Hello World DI
• Using setter, Constructor Injection
• Injecting Objects
• Inner Beans, Aliases
• Initializing Collections
• Understanding Bean Scopes
• Bean Autowiring
• Using ApplicationContextAware
• Bean Definition Inheritance
• Lifecycle Callbacks
• Method injections
• Lookup method injection
• …
• …


Introduction to DI


interface

Design as per interface


Car depends on Wheel


Most important :glue it all with XML


DI ?
• DI is how objects or bean using Spring are brought together by container
to accomplished the task

• It is AKA of IoC

• In most application and object is responsible for its own dependencies or
associated objects and this is mostly achieved using JNDI

• In DI approach we allow container to manages dependencies of object
creation and association

Hollywood ; don’t call me I will call you



How Spring Work?


• Any object outside
container get bean by
providing ref

• We know object requiring
bean contact to container ie
Application context that
refer SpringXML and create
a Spring managed bean and
that can be referred by
requesting object
outside/inside the
container


Spring Hello world example


Setter injection….Ex


Injecting Objects


Inner Beans
• Remove the definition of
Point bean and put into
triangle bean

• Remove the ref tag and put
definition inside.

• No performance adv.

• whenever a bean is used for
only one particular property,
it’s advise to declare it as an
inner bean

Aliases

• alias giving name
to same bean
• Use alias tag
• Now bean can be
referred by new
name


Spring bean scopes

• In Spring, bean scope is used to decide which
type of bean instance should be return from
Spring container back to the caller.

• In most cases, you may only deal with the
Spring’s core scope – singleton and prototype,
and the default scope is singleton.


Bean Scopes
Scope Description
Singleton (Default)Only one single instance will be
created

Prototype Creates any number of instances from a
single bean configuration

Request Scope of the bean instance will be limited to
the Request life cycle

Session Limited to session

Global session Limited to global session- Portlet context.

<bean name =“student” class =“Student” scope =“prototype”/>

Singleton scope
ctx.getBean(“student”)

Spring
Container Single student
instance


Output in case of
default bean scope


Prototype scope
ctx.getBean(“student”)

Spring
Container
Multiple Beans


Spring Collection
• What if member variable is collection
major collection types are supported in
Spring

List – <list/>
Set – <set/>
Map – <map/>
Properties – <props/>


Injecting list..


Auto Wiring

• Skip some of the configuration that we have
to do by intelligent guessing what ref is
• AKA shortcut.
• Type of auto wiring
– byName
– byType (for only one composite object)
– constructor


<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation=" http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">

<bean id="tringle" class="com.ex3.code.Tringle" autowire="byName">

</bean>

<bean id="pointA" class="com.ex3.code.Point">
<property name="x" value="0"/>
<property name="y" value="0"/>
</bean>

<bean id="pointB" class="com.ex3.code.Point">
</bean>

<bean id="pointC" class="com.ex3.code.Point">
<property name="x" value="-20"/>
</bean>

<alias name="tringle" alias="my-tringle"/>

</beans>


Aware interfaces..

• BeanName Aware interface
• Want to know the name of bean configured
• ApplicationContextAware
• Getting Application context
• We need to implements ApplicationContextAware

Container itself call setter related to aware interface
before creation of any bean.


Bean Definition Inheritance
• Lets say we have 100 bean definition in xml ,
lets we have common definition in each bean
definition aka template


<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

<bean id="parenttringle" class="com.ex3.code.Tringle">
<property name="pointA" ref="firstPoint"></property>
</bean>

<bean id="tringle" class="com.ex3.code.Tringle" parent="parenttringle">
<property name="pointC" ref="secPoint"></property>
<property name="pointC" ref="thirdPoint"></property>
</bean>

<bean id="firstPoint" class="com.ex3.code.Point">
</bean>

<bean id="secPoint" class="com.ex3.code.Point">
</bean>

<bean id="thirdPoint" class="com.ex3.code.Point">
<property name="x" value="-20"/>
</bean>

<alias name="tringle" alias="my-tringle"/>

</beans>


Lifecycle Callbacks
• Spring provide us call-back method for life cycle
of bean
• for initialization of bean
• for cleanup of bean

EX: Shut down hook
• closing app context for SE applications
• use class AbstractAppicationContext, when main finished

AbstractApplicationContext ctx=new ClassPathXmlApplicationContext("springWithAutoWiring.xml");
ctx.registerShutdownHook();


cofig init and destroyed method
• Choice I
• implements InitializingBean,DisposableBean
• Choice II
• Dont want to bind to spring interface interfaces......

<bean id="tringle" class="com.ex3.code.Tringle" autowire="byName" init-method="myInit" destroy-
method="myDestroy">

What happens if both are there?
first spring then my method is called.


public class Tringle implements
public void setPointC(Point pointC) {
InitializingBean,DisposableBean{ this.pointC = pointC;
}
private Point pointA; public void draw() {
private Point pointB; System.out.println(pointA);
System.out.println(pointB);
private Point pointC; System.out.println(pointC);
}
public Point getPointA() {
@Override
return pointA; public void afterPropertiesSet() throws Exception {
// TODO Auto-generated method stub
} System.out.println("called after init of bean");
public void setPointA(Point pointA) { }
@Override
this.pointA = pointA; public void destroy() throws Exception {
System.out.println("called after destruction of bean");
} }

public Point getPointB() {
}
return pointB; }
}
public void setPointB(Point pointB) {
this.pointB = pointB;
}
public Point getPointC() {
return pointC;
}


Method Injection – Method Replace
class MobileStore{
public String buyMobile(){
return "Bought a Mobile Phone";
}}

class MobileStoreReplacer implements MethodReplacer{
public Object reimplement(Object obj, Method method, Object[] args)
throws Throwable{
return “Bought an iPhone”;

}
}

<bean id =“mobileStore” class =“MobileStore”>
<replace-method name =“buyMobile” replacer =“mobileStoreReplacer”/>
</bean>

<bean id =“mobileStoreReplacer” class =“MobileStoreReplacer”/>

Lookup Method Injection
public abstract class BookStore { public interface Book {
public String bookTitle();
public abstract Book orderBook(); }
}
Managed by Spring
public class StoryBook implements Book{ public class ProgrammingBook
public String bookTitle() { implements Book{
return "HarryPotter“; } public String bookTitle() {
} return "spring programming“; }
}

• The ability of the container to override methods on
container managed beans, to return the lookup
result for another named bean in the container.


Thanks !!!


Spring 3.0 dependancy injection

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