JAVA EE: Spring Bean Life Cycle - ApplicationContextAware Interface

Friday, 24 August 2018

Spring Bean Life Cycle - ApplicationContextAware Interface | Spring Tutorial

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What is the ApplicationContextAware Interface?

In the Spring Framework, the ApplicationContextAware interface allows a bean to obtain a reference to the ApplicationContext that created it. By implementing this interface, a bean gets direct access to advanced container capabilities such as loading file resources, publishing events, accessing internationalized messages, and dynamically retrieving other beans.

How Does ApplicationContextAware Fit into the Bean Life Cycle?

During the bean lifecycle management phase:

The container instantiates the bean and sets all configured property values.
Spring checks if the bean implements ApplicationContextAware.
The container calls the callback method setApplicationContext(ApplicationContext context) to inject the running context instance.
The bean stores the context object and uses it for runtime container operations.

Example Implementation

public class ApplicationContextAwareImpl implements ApplicationContextAware {
    private ApplicationContext context;

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

    public void displayDetails() {
        Employee emp = context.getBean("employee", Employee.class);
        System.out.println("Employee Details: " + emp);
    }
}

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Spring Bean Life Cycle - ApplicationContextAware Interface | Spring Tutorial

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;

    }

    @Override

    public String toString()

    {

        return "Employee [name=" + name + "]";

    }

}

ApplicationContextAwareImpl.java

package com.ram.contextaware;

import org.springframework.beans.BeansException;

import org.springframework.context.ApplicationContext;

import org.springframework.context.ApplicationContextAware;

import com.ram.model.Employee;

public class ApplicationContextAwareImpl implements ApplicationContextAware

{

    private ApplicationContext applicationContext;

    public void setApplicationContext(ApplicationContext applicationContext)

            throws BeansException

    {

        System.out.println(

                "setApplicationContext method called by the Spring Container");

        this.applicationContext = applicationContext;

    }

    public void displayEmployeeDetails()

    {

        Employee employee = applicationContext.getBean("employee",

                Employee.class);

        System.out.println(

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

                        + employee);

        System.out.println("is employee object Singleton? = "

                + applicationContext.isSingleton("employee"));

    }

}

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="applicationContextAware" class="com.ram.contextaware.ApplicationContextAwareImpl" />

</beans>

App.java

package com.ram.core;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.ram.contextaware.ApplicationContextAwareImpl;

public class App

{

    public static void main(String[] args)

    {

        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext(

                "applicationContext.xml");

        ApplicationContextAwareImpl applicationContextAwareImpl = applicationContext

                .getBean("applicationContextAware",

                        ApplicationContextAwareImpl.class);

        applicationContextAwareImpl.displayEmployeeDetails();

        applicationContext.close();

    }

}

Output

Aug 11, 2018 11:11:22 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Sat Aug 11 11:11:22 IST 2018]; root of context hierarchy

Aug 11, 2018 11:11:23 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

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

setApplicationContext method called by the Spring Container

Got employee object from the ApplicationContext(Spring Container) = Employee [name=Peter]

is employee object Singleton? = true

Aug 11, 2018 11:11:23 AM org.springframework.context.support.AbstractApplicationContext doClose

INFO: Closing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Sat Aug 11 11:11:22 IST 2018]; root of context hierarchy