JAVA EE: Event handling in spring [ContextStartedEvent and ContextStoppedEvent]

Sunday, 23 September 2018

Event handling in spring [ContextStartedEvent and ContextStoppedEvent] | Spring event handling

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Overview: ContextStartedEvent and ContextStoppedEvent in Spring

The Spring Framework provides built-in lifecycle management events via the ApplicationContext. Beyond context refresh and close events, Spring provides ContextStartedEvent and ContextStoppedEvent to control explicit lifecycle phases for components and background tasks.

In this guide, you will learn what these two lifecycle events represent, when they are triggered, and how to create custom listeners to handle them effectively.

Understanding ContextStartedEvent & ContextStoppedEvent

Unlike refresh events which fire automatically during bootstrap, start and stop events are tied to explicit lifecycle calls on ConfigurableApplicationContext:

ContextStartedEvent: Published when the ApplicationContext is started using the start() method on ConfigurableApplicationContext. All Lifecycle beans receive an explicit start signal, making it useful for starting background threads, pollers, or scheduled jobs.
ContextStoppedEvent: Published when the ApplicationContext is stopped using the stop() method on ConfigurableApplicationContext. All Lifecycle beans receive an explicit stop signal, making it ideal for pausing background tasks without destroying the context.

Step-by-Step Implementation

Create Event Listeners: Define listener classes implementing ApplicationListener<ContextStartedEvent> and ApplicationListener<ContextStoppedEvent>.
Override onApplicationEvent: Implement the onApplicationEvent(...) method in each listener to handle start and stop actions.
Invoke start() and stop(): Call context.start() and context.stop() on your ConfigurableApplicationContext instance to trigger the events.

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Event handling in spring [ContextStartedEvent and ContextStoppedEvent] | Spring event handling

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0%20http://maven.apache.org/maven-v4_0_0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.ram.core</groupId>

    <artifactId>SpringDemo</artifactId>

    <packaging>jar</packaging>

    <version>1.0-SNAPSHOT</version>

    <name>SpringDemo</name>

    <url>http://maven.apache.org</url>

    <properties>

        <spring.version>5.0.2.RELEASE</spring.version>

    </properties>

    <dependencies>

        <dependency>

            <groupId>junit</groupId>

            <artifactId>junit</artifactId>

            <version>3.8.1</version>

            <scope>test</scope>

        </dependency>

        <!-- Spring 5 dependencies -->

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-core</artifactId>

            <version>${spring.version}</version>

        </dependency>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-context</artifactId>

            <version>${spring.version}</version>

        </dependency>

    </dependencies>

</project>

Employee.java

package com.ram.model;

/**

 * Spring bean

 *

 */

public class Employee

{

    private String name;

    public void setName(String name)

    {

        this.name = name;

    }

    public void employeeDetails()

    {

        System.out.println("Employee Name =  " + name);

    }

}

ContextStartEventHandler.java

package com.ram.eventhandler;

import org.springframework.context.ApplicationListener;

import org.springframework.context.event.ContextStartedEvent;

public class ContextStartEventHandler implements ApplicationListener<ContextStartedEvent>

{

    public void onApplicationEvent(ContextStartedEvent event)

    {

        System.out.println("ContextStartedEvent Received = "+ event);

    }

}

ContextStopEventHandler.java

package com.ram.eventhandler;

import org.springframework.context.ApplicationListener;

import org.springframework.context.event.ContextStoppedEvent;

public class ContextStopEventHandler implements ApplicationListener<ContextStoppedEvent>

{

    public void onApplicationEvent(ContextStoppedEvent event)

    {

        System.out.println("ContextStoppedEvent Received = "+event);

    }

}

applicationContext.xml

<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-4.3.xsd">

    <bean id="employee" class="com.ram.model.Employee">

        <property name="name" value="Peter" />

    </bean>

    <bean id="contextStartEventHandler" class="com.ram.eventhandler.ContextStartEventHandler" />

    <bean id="contextStopEventHandler" class="com.ram.eventhandler.ContextStopEventHandler" />

</beans>

App.java

package com.ram.core;

import org.springframework.context.ConfigurableApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.ram.model.Employee;

public class App

{

    public static void main(String[] args)

    {

        ConfigurableApplicationContext context = new ClassPathXmlApplicationContext(

                "applicationContext.xml");

        context.start();

        System.out.println("---------------------------------------");

        Employee employee = (Employee) context.getBean("employee");

        System.out.println(

                "Got employee object from the ApplicationContext(Spring Container)");

        employee.employeeDetails();

        System.out.println("---------------------------------------");

        context.stop();

    }

}

Output

Aug 25, 2018 10:35:16 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@610694f1: startup date [Sat Aug 25 10:35:16 IST 2018]; root of context hierarchy

Aug 25, 2018 10:35:16 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

INFO: Loading XML bean definitions from class path resource [applicationContext.xml]

ContextStartedEvent Received = org.springframework.context.event.ContextStartedEvent[source=org.springframework.context.support.ClassPathXmlApplicationContext@610694f1: startup date [Sat Aug 25 10:35:16 IST 2018]; root of context hierarchy]

---------------------------------------

Got employee object from the ApplicationContext(Spring Container)

Employee Name =  Peter

---------------------------------------

ContextStoppedEvent Received = org.springframework.context.event.ContextStoppedEvent[source=org.springframework.context.support.ClassPathXmlApplicationContext@610694f1: startup date [Sat Aug 25 10:35:16 IST 2018]; root of context hierarchy]