JAVA EE: Spring Bean Life Cycle - BeanPostProcessor

Wednesday, 22 August 2018

Spring Bean Life Cycle - BeanPostProcessor | Spring Tutorial

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What Is a BeanPostProcessor in Spring?

The BeanPostProcessor is a powerful interface provided by the Spring Framework that allows developers to customize and modify bean instances during their initialization phase.

Unlike standard bean configuration, a BeanPostProcessor operates on newly created bean instances globally across your Spring container, giving you complete hooks before and after initialization callbacks execute.

Core Methods of BeanPostProcessor

Implementing the BeanPostProcessor interface gives you access to two fundamental lifecycle callback methods:

postProcessBeforeInitialization(Object bean, String beanName): Executes before any custom bean initialization logic (like @PostConstruct or custom init-method). This is ideal for validating properties or wrapping beans.
postProcessAfterInitialization(Object bean, String beanName): Executes after initialization callbacks have finished. This is commonly used for creating AOP proxies, applying security checks, or decorating bean instances.

Why Use BeanPostProcessor in Your Applications?

Cross-Cutting Customization: Apply common setup, logging, or verification logic to multiple beans automatically without duplicating code.
Custom Annotation Processing: Scan for custom annotations and configure beans dynamically at startup.
Proxy Creation: Wrap target objects inside dynamic proxies to inject behaviors like transaction management and profiling.

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Spring Bean Life Cycle - BeanPostProcessor | 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 + "]";

    }

}

Fruit.java

package com.ram.model;

/**

 * Spring bean

 */

public class Fruit

{

    private String name;

    public void setName(String name)

    {

        this.name = name;

    }

    @Override

    public String toString()

    {

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

    }

}

MyBeanPostProcessor.java

package com.ram.postprocessor;

import org.springframework.beans.BeansException;

import org.springframework.beans.factory.config.BeanPostProcessor;

public class MyBeanPostProcessor implements BeanPostProcessor

{

    public Object postProcessBeforeInitialization(Object bean, String beanName)

            throws BeansException

    {

        System.out.println("Post Process Before Initialization for the bean = "

                + beanName);

        return bean;

    }

    public Object postProcessAfterInitialization(Object bean, String beanName)

            throws BeansException

    {

        System.out.println(

                "Post Process After Initialization for the bean = " + beanName);

        return bean;

    }

}

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="fruit" class="com.ram.model.Fruit">

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

    </bean>

    <!-- This post processor methods are called for every bean -->

    <bean class="com.ram.postprocessor.MyBeanPostProcessor" />

</beans>

App.java

package com.ram.core;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.ram.model.Employee;

import com.ram.model.Fruit;

public class App

{

    public static void main(String[] args)

    {

        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(

                "applicationContext.xml");

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

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

        System.out.println(

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

                        + employee);

        Fruit fruit = context.getBean("fruit", Fruit.class);

        System.out.println(

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

                        + fruit);

        context.registerShutdownHook();

    }

}

Output

Aug 08, 2018 10:06:50 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Wed Aug 08 10:06:50 IST 2018]; root of context hierarchy

Aug 08, 2018 10:06:50 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

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

Post Process Before Initialization for the bean = employee

Post Process After Initialization for the bean = employee

Post Process Before Initialization for the bean = fruit

Post Process After Initialization for the bean = fruit

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

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

Got fruit object from the ApplicationContext(Spring Container) = Fruit [name=Apple]