Spring Bean Life Cycle - Spring @PostConstruct and @PreDestroy Annotations | Spring Tutorial

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What Are @PostConstruct and @PreDestroy Annotations?

In the Spring Framework, managing the lifecycle of a bean is essential for initializing resources and ensuring clean shutdowns. The @PostConstruct and @PreDestroy annotations are part of the standard Java annotations (JSR-250) supported seamlessly by Spring.

They offer a clean, readable, annotation-driven approach to execute custom startup and teardown logic without coupling your classes to Spring-specific interfaces.

Understanding @PostConstruct

The @PostConstruct annotation is placed on a method that needs to run immediately after dependency injection is complete and the bean has been fully initialized.

• Initialization Logic: Ideal for loading configuration files, opening database connections, or pre-caching required data.
• Safety: Guarantees that all autowired properties and dependencies are ready to use.

Understanding @PreDestroy

The @PreDestroy annotation marks a callback method that executes just before the Spring container destroys the bean instance during application shutdown.

• Resource Cleanup: Used to close open streams, release file locks, or shut down active worker threads safely.
• Graceful Shutdown: Prevents memory leaks and connection hanging when your application stops.

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Spring Bean Life Cycle - Spring @PostConstruct and @PreDestroy Annotations | Spring Tutorial

Spring Bean Life Cycle - Spring @PostConstruct and @PreDestroy Annotations | Spring Tutorial

Spring Bean Life Cycle - Spring @PostConstruct and @PreDestroy Annotations | 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;

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

public class Employee
{
    private int id;
    private String name;

    public int getId()
    {
        return id;
    }

    public void setId(int id)
    {
        this.id = id;
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    @PostConstruct
    public void init() throws Exception
    {
        System.out.println("inside Init method after properties are set. ");
    }
   
    @PreDestroy
    public void cleanUp() throws Exception
    {
        System.out.println("Inside cleanUp(), Performed clean up tasks.");
    }

    @Override
    public String toString()
    {
        return "Employee [id=" + id + ", name=" + name + "]";
    }

}

applicationContext.xml

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-4.3.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-4.3.xsd">

    <bean id="employee" class="com.ram.model.Employee" >
        <property name="id" value="100"></property>
        <property name="name" value="Peter"></property>
    </bean>

    <context:annotation-config />

</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");

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

        Employee employee = context.getBean("employee", Employee.class);
        System.out.println(
                "Got employee object from the ApplicationContext(Spring Container)");

        System.out.println(employee);

        context.close();
    }

}

Output

Aug 07, 2018 10:27:26 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Tue Aug 07 10:27:26 IST 2018]; root of context hierarchy
Aug 07, 2018 10:27:26 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [applicationContext.xml]
inside Init method after properties are set.
---------------------------------------
Got employee object from the ApplicationContext(Spring Container)
Employee [id=100, name=Peter]
Aug 07, 2018 10:27:26 AM org.springframework.context.support.AbstractApplicationContext doClose
INFO: Closing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Tue Aug 07 10:27:26 IST 2018]; root of context hierarchy
Inside cleanUp(), Performed clean up tasks.

Click the below link to download the code:
https://sites.google.com/site/ramj2eev2/java_basics/SpringDemo_PostConstruct_PreDestroy.zip?attredirects=0&d=1

Github Link:
https://github.com/ramram43210/javaee/tree/master/Spring_2018/SpringDemo_PostConstruct_PreDestroy

Bitbucket Link:
https://bitbucket.org/ramram43210/spring/src/924507f5515578f632825f98c99b1cb6c7d7a7be/Spring_2018/SpringDemo_PostConstruct_PreDestroy/?at=master

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