Event Handling in Spring

Spring Framework also provide an another feature to promote loose coupling ,which is Application Event handling. Using Events, an Event publisher object can communicate with other objects without even knowing which object is listen.and event listener can work to event without knowing which object publish the events. Publisher Object that object ,who publish the event or call the event and Listener always listen the events that are occurs.

To make a custom event extends the class with ApplicationEvent class.The ApplicationEventPublisher has contain publishEvent() method that enable to publish ApplicationEvents (Custom Events).Any ApplicationListener that is registered with the onApplicationEvent() method in application,listen the events.
To understand The Event handling Lets illustrate a simple example-

Circle.java
package com.dineshonjava.sdnext.eventHandling.tutorial;

import javax.annotation.Resource;

import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationEventPublisherAware;
import org.springframework.context.MessageSource;
import org.springframework.stereotype.Controller;

/**
 * @author Dinesh Rajput
 *
 */
@Controller
public class Circle implements ApplicationEventPublisherAware
{
 private Point             center;
 private ApplicationEventPublisher publisher;
 
 /**
  * @param center the center to set
  */
 @Resource(name="pointB")
 public void setCenter(Point center)
 {
  this.center = center;
 }

 public void draw()
 {
             System.out.println("Circle is Drawn");
             DrawEvent drawEvent = new DrawEvent(this);
             publisher.publishEvent(drawEvent);
 }

 @Override
 public void setApplicationEventPublisher(ApplicationEventPublisher publisher)
 {
  this.publisher = publisher;
 }
}
Point.java
package com.dineshonjava.sdnext.eventHandling.tutorial;

/**
 * @author Dinesh Rajput
 *
 */
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;
 } 
}
MyEventListener.java
package com.dineshonjava.sdnext.eventHandling.tutorial;

import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.stereotype.Component;

@Component
public class MyEventListener implements ApplicationListener
{

 @Override
 public void onApplicationEvent(ApplicationEvent event) 
 {
  System.out.println(event.toString());
 }

}
DrawEvent.java
package com.dineshonjava.sdnext.eventHandling.tutorial;

import org.springframework.context.ApplicationEvent;

public class DrawEvent extends ApplicationEvent
{

 /**
  * Dinesh Rajput
  */
 private static final long serialVersionUID = 6973014356268900607L;

 public DrawEvent(Object source)
 {
  super(source);
 }
 
 public String toString()
 {
  return "Draw event occurred";
 }
}
spring.xml
<beans xmlns:context="http://www.springframework.org/schema/context" 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.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
<context:annotation-config></context:annotation-config>
<bean class="com.sdnext.dineshonjava.eventHandling.tutorial.Point" id="pointB">
    <property name="x" value="10"></property>
    <property name="y" value="20"></property>
</bean>
<context:component-scan base-package="com.sdnext.dineshonjava.eventHandling.tutorial"></context:component-scan>
</beans>
DrawingApp.java
package com.dieshonjava.sdnext.eventHandling.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");
Circle circle = (Circle)context.getBean("circle");
circle.draw();
 }
}

Output:
Circle is Drawn
Draw event occurred






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