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Using ApplicationContextAware in Spring

In this chapter we will show you a short hint how you can access your Spring-ApplicationContext from everywhere in your Application.

We'll provide our beans with access to the ApplicationContext object by implementing the ApplicationContextAware interface. We'll also use BeanNameAware interface to get the name of the bean configured in the Spring XML.
ApplicationContextAware in Spring
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WHY ApplicationContextAware?

Imagine we have an application (e.g. a web or swing-application) which we now want to be Spring-enabled. Ok we add the Spring libraries(spring.jar) and the Configuration-file(spring.xml) and create our Spring-beans. But there are still some old class-files which you can’t use in this way. These files still need access to the Spring-Honeypot where all the goodies exists and you don’t want to redesign your application.
First create the class "ApplicationContextProvider (Triangle class)". This   class    implements    the ApplicationContextAware. A bean which implements the ApplicationContextAware-interface and is deployed into the context, will be called back on creation of the bean, using the interface’s setApplicationContext(…) method, and provided with a reference to the context, which may be stored for later interaction with the context.

In this tutorial you will see and example of using ApplicationContextAware. The ApplicationContextAware is used when an object required. 

Triangle.java
package com.dineshonjava.sdnext.contextAware.tutorial;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanNameAware;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

public class Triangle implements ApplicationContextAware, BeanNameAware
{
 private Point pointA;
 private Point pointB;
 private Point pointC;
 private ApplicationContext context = null;
 
 /**
  * @param pointA the pointA to set
  */
 public void setPointA(Point pointA) {
  this.pointA = pointA;
 }

 /**
  * @param pointB the pointB to set
  */
 public void setPointB(Point pointB) {
  this.pointB = pointB;
 }

 /**
  * @param pointC the pointC to set
  */
 public void setPointC(Point pointC) {
  this.pointC = pointC;
 }

 public void draw()
 {
System.out.println("PointA is ("+pointA.getX()+", "+pointA.getY()+")");
System.out.println("PointB is ("+pointB.getX()+", "+pointB.getY()+")");
System.out.println("PointC is ("+pointC.getX()+", "+pointC.getY()+")");
 }

 @Override
 public void setApplicationContext(ApplicationContext context) throws BeansException
 {
  this.context = context;
 }

 @Override
 public void setBeanName(String beanName)
 {
  System.out.println("Bean name is: "+beanName);
 }
}
Point.java
package com.dineshonjava.sdnext.contextAware.tutorial;

public class Point
{
 private int x;
 private int y;
 /**
  * @return the x
  */
 public int getX() {
  return x;
 }
 /**
  * @param x the x to set
  */
 public void setX(int x) {
  this.x = x;
 }
 /**
  * @return the y
  */
 public int getY() {
  return y;
 }
 /**
  * @param y the y to set
  */
 public void setY(int y) {
  this.y = y;
 }
}
spring.xml
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.springframework.org/schema/beans" xsi:schemalocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
 <bean autowire="byName" class="com.dineshonjava.sdnext.contextAware.tutorial.Triangle" id="triangle"></bean>
  
<bean class="com.dineshonjava.sdnext.contextAware.tutorial.Point" id="pointA">
  <property name="x" value="0"></property>
  <property name="y" value="0"></property>
</bean>
  
<bean class="com.dineshonjava.sdnext.contextAware.tutorial.Point" id="pointB">
  <property name="x" value="-20"></property>
  <property name="y" value="0"></property>
</bean>
  
<bean class="com.dineshonjava.sdnext.contextAware.tutorial.Point" id="pointC">
   <property name="x" value="20"></property>
   <property name="y" value="0"></property>
</bean>
</beans>
DrawingApp.java
package com.sdnext.contextAware.tutorial;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @author Dinesh Rajput
 *
 */
public class DrawingApp 
{
 /**
  * @param args
  */
 public static void main(String[] args) 
 {
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
Triangle triangle = (Triangle) context.getBean("triangle");
triangle.draw();
 }
}
Output:
Jun 30, 2012 3:28:54 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@145d068: startup date [Sat Jun 30 15:28:54 IST 2012]; root of context hierarchy
Jun 30, 2012 3:28:55 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [spring.xml]
Jun 30, 2012 3:28:55 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@f11404: defining beans [triangle,pointA,pointB,pointC]; root of factory hierarchy
Bean name is: triangle
PointA is (0, 0)
PointB is (-20, 0)
PointC is (20, 0)

What is Need for Using ApplicationContextAware in Application? In previous chapter we have seen that we create applicationcontext object via using configuration file(spring.xml) but we done this only one time of the applicationcontext object using configuration file (spring.xml) for entire application.

If we done one time creating applicationcontext object and also one time creating triangle bean through the getBean() method because its have "singleton" scope and beans pointA, pointB & pointC are also populated along with triangle bean only one time when triangle bean is initialized even though pointA, pointB & pointC are the prototype in scope.

After that we can not create as new bean pointA, pointB & pointC objects without creating triangle bean in the Triangle class or anywhere else except main app(DrawingApp.java).

And there are some situation we want to use applicationcontext object any where else like in bean class(in Triangle class). Suppose the Triangle bean need to applicationcontext object for some reasons.


Suppose If we want to create new beans pointA, pointB & pointC in triangle class then we have to declare  pointA, pointB & pointC beans as prototype bean scope. Now we have need to access applicationContext object in the triangle bean class so because of this     we     are       used ApplicationContextAware intreface and this interface is implements by the Triangle bean class for accessing applicationcontext object from    overriding    the    following     method    of            the ApplicationContextAware interface.

@override
public void setApplicationContext(ApplicationContext context) throws BeansException
{
  this.context = context;
}

In Next Chapter we will discuss about Bean Definition Inheritance in Spring in Application.

                                          
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