Spring - Bean Life Cycle

shahbaz peerzade

5 Aug 2022

Bean Lifecycle

When the beans get instantiated it is required to perform some initialization to get it to an unstable state. Also, when the bean is no longer required and gets removed from the IoC container some clean-up is required. There are lists of things that take place behind during the time of the initialization of the bean and its destruction. You will declare the bean using <bean> with init method and destroy-method

Bean life cycle is managed by the spring container. When we run the program then, first of all, the spring container gets started. After that, the container creates the instance of a bean as per the request, and then dependencies are injected. And finally, the bean is destroyed when the spring container is closed. Therefore, if we want to execute some code on the bean instantiation and just after closing the spring container, then we can write that code inside the custom init() method and the destroy() method.

Bean Life Cycle Process Flow

Ways to implement the life cycle of a bean

Spring provides three ways to implement the life cycle of a bean. In order to understand these three ways, Therefore, the three ways to implement this are:

1. By XML:

2. By Programmatic Approach:

3. Using Annotation:

Spring Bean Life Cycle – Initialization and Destruction

Bean Life Cycle-Initialisation and Destruction

a. Initialisation Callbacks

Inside the method afterPropertiesSet() implement the interface org.spring framework,beans.factory.InitializingBean and do the initialization work

b. Destruction Callbacks

Inside the method destroy() implement the interface org.spring framework,beans.factory.InitializingBean and do the initialization work

       <bean id = "exampleBean" class = "examples.ExampleBean" destroy-method = "destroy"/>

c. Default Initialization and Destroy Methods

You don’t need the declaration of the methods in it and destroy if there are many beans with initialization and destroy methods having the same names. Instead, you have default init and destroy methods

Example

Here is the content of HelloWorld.java file −

package com. example;

public class HelloWorld {

private String message;

public void setMessage(String message){

this.message = message;

}

public void getMessage(){

System.out.println("Your Message : " + message);

}

public void init(){

System.out.println("Bean is going through init.");

}

public void destroy() {

System.out.println("Bean will destroy now.");

}

configuration file Beans.xml

<?xml version="1.0" encoding="UTF-8"?>

<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.xsd">

<bean id = "helloWorld" class = "com.example.HelloWorld" init-method = "init"

destroy-method = "destroy">

</bean>

</beans>

MainApp.java

package com.example;

import org.springframework.context.support.AbstractApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {

public static void main(String[] args) {

AbstractApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");

HelloWorld obj = (HelloWorld) context.getBean("helloWorld");

obj.getMessage();

context.destroy();

}

//Output

//Output
    Bean is going through init.
    Your  Message: Hello World!
    Bean will destroy now.