How spring bean life cycle – bean initialization and destruction?

The Spring container is responsible for instantiating, configuring and assembling objects known as beans, as well as managing their life-cycle, the life cycle of beans consist of call back methods (init-method and destroy-method). Below steps are followed by Spring IoC Container to manage bean life cycle.

Spring Bean Life Cycle :

1.) Instantiate the bean : Hare spring container is responsible to instantiation of bean  object.

2.) Properties Injection : Hare Inversion Of Control is applied.

3.) Set the Bean Name : execute the life-cycle method setBeanName() of BeanAwareInterface that is responsible to set the name of bean in bean factory.

4.) Load bean by setBeanClassLoader() : Method of that BeanClassLoaderAware Interface. It has to provide implementation to setBeanClassLoader(). This method called by the passing an instance of class loader object that class loaded this bean.
5.) Call setBeanFactory() : Method of BeanFactoryAware Interface.If a bean has implemented beanFactoryAware Interface, it has to provide implementation of setBeanFactory(). This method called by the passing an instance of bean factory object.
6.) postProcessBeforeInicilization() : Method of beanPostProcessor Interface. It has to provide implementation to postProcessBeforeInicilization(). This method will be called given new been instance before any bean initialization callbacks.
7.) afterPropertiesSet() : This method called by the bean factory to set after bean properties.
8.) Custom Int Method : Hare custom initialization method will be called.
9.) PostProcessAfterInicilization() : This method will be called given new been instance after any bean initialization callbacks.
10.) destroy() :When application no longer required bean references.
11.) In last process destroy the custom bean object.

Spring can recognize the initialization and destruction callback methods in the below three ways.

1. A Bean can implement the InitializingBean and DisposableBean life cycle interfaces and overriding the afterPropertiesSet() (Called during Spring bean initialization) and destroy() methods for initialization and destruction respectively.
2. Set the init-method and destroy-method attributes in the bean configuration file.
3. Use @PostConstruct and @PreDestroy over the methods (Spring 2.5 or later) which is defined in JSR-250.

   Lets learn about each one of them one by one.

   1. Implementing InitializingBean and DisposableBean Interfaces

   When are implement the InitializingBean and DisposableBean interfaces in our bean, Spring allows our bean to perform the task mentioned initialization and destruction methods afterPropertiesSet() and destroy(). During the construction you can notice Spring will be calling those methods at a suitable time of Spring bean life cycle.
   

   Folder Structure:

4. Create a new Java Project  “SpringCoreTutorial” and create a package for our src files “com.javainterviewpoint“
5. Add the required libraries to the build path. Java Build Path ->Libraries ->Add External JARs and add the below jars.
   

   commons-logging-1.2.jar
   spring-beans-4.2.4.RELEASE.jar
   spring-core-4.2.4.RELEASE.jar
   spring-context-4.2.4.RELEASE.jar
   spring-expression-4.2.4.RELEASE.jar

6. Create the Java classes InitializeDestroyExample.java and Logic.java under  com.javainterviewpoint folder.
7. Place our configuration file SpringConfig.xml in the src directory

SpringConfig.xml

In order to declare beans in the Spring IoC container via XML, we must create an XML configuration file (SpringConfig.xml). The configuration file must be put in the src directory.

<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-3.0.xsd
 http://www.springframework.org/schema/context
 http://www.springframework.org/schema/context/spring-context-3.0.xsd">
 
    <context:annotation-config></context:annotation-config>
 
    <bean id="initdest" class="com.javainterviewpoint.InitializeDestroyExample"></bean>
 
</beans>

We have made an entry for our bean “InitializeDestroyExample” with id “initdest”.

InitializeDestroyExample.java

package com.javainterviewpoint;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;

public class InitializeDestroyExample implements InitializingBean, DisposableBean
{
    @Override
    public void afterPropertiesSet() throws Exception
    {
        System.out.println("Initialization method called");
    }
    
    @Override
    public void destroy() throws Exception
    {
        System.out.println("Destroy method called");
    }
    
    public void display()
    {
        System.out.println("Welcome to JavaInterviewPoint!!!");
    }
}

In our InitializeDestroyExample class we have implemented the InitializingBean and DisposableBean interfaces and overridden the afterPropertiesSet() and destroy() methods. We have a concrete method display() which displays the welcome message.

Logic.java

package com.javainterviewpoint;

import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Logic
{
    public static void main(String args[])
    {
        // Read the Configuration file using ApplicationContext
        AbstractApplicationContext applicationContext = 
                new ClassPathXmlApplicationContext("SpringConfig.xml");

        // Get the InitializeDestroyExample class instance
        InitializeDestroyExample id = 
                (InitializeDestroyExample) applicationContext.getBean("initdest");
        // Call the display() method
        id.display();

        // Closing the context
        applicationContext.close();
    }
}

• In our Logic class we have read the Configuration file(SpringConfig.xml) and get all the bean definition through ApplicationContext
• Get the InitializeDestroyExample Class instance by calling the getBean() method over the context created.
• Call the display() which prints the welcome message.
• Finally Close the application context which we have created.

Output :
Upon running our Logic class we will be getting the below output.

2. init-method and destroy-method Attributes in the Configuration file

In the above way we are forced to implement the InitializingBean and DisposableBean interfaces and overridde the afterPropertiesSet() and destroy() methods. By setting the init-method and destroy-method attribute in the configuration file. we can have our own custom method acting as a initializing and destroy method. Lets now re-write the InitializeDestroyExample class.

InitializeDestroyExample.java

package com.javainterviewconcept;

public class InitializeDestroyExample
{
    public void initializationMethod()
    {
        System.out.println("Initialization method called");
    }
    
    public void display()
    {
        System.out.println("Welcome to javainterviewconcept!!!");
    }
    
    public void destroyMethod()
    {
        System.out.println("Destroy method called");
    }
}

We have written our own methods intializationMethod() and destroyMethod() for spring bean initialization and spring bean destruction respectively.
Now corresponding changes has to be made in our configuration file

<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-3.0.xsd
 http://www.springframework.org/schema/context
 http://www.springframework.org/schema/context/spring-context-3.0.xsd">
 
    <context:annotation-config></context:annotation-config>
 
    <bean id="initdest" class="com.javainterviewconcept.InitializeDestroyExample" 
          init-method="initializationMethod" destroy-method="destroyMethod"/>
 
</beans>

We have added the init-method attribute value as “initializationMethod” for initialization and destroy-method attribute value as “destroyMethod” for destruction.
Output :
Upon running our Logic class we will be getting the below output.

Jun 20, 2016 5:02:37 PM org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor 
INFO: JSR-330 'javax.inject.Inject' annotation found and supported for autowiring
Initialization method called
Welcome to javainterviewconcept!!!
Jun 20, 2016 5:02:37 PM org.springframework.context.support.ClassPathXmlApplicationContext doClose
INFO: Closing org.springframework.context.support.ClassPathXmlApplicationContext@544764a1: startup date [Mon Jun 20 17:02:37 IST 2016]; root of context hierarchy
Destroy method called

3. Using @PostConstruct and @PreDestroy Annotations

Using the @PostConstruct and @PreDestroy annotation would be much simpler approach those are the spring bean life cycle annotation, we can remove of the init-method and destroy-method attribute in our configuration file and simply add the @PostConstruct annotation over the method which you want to be called after spring bean initialization and @PreDestroy over the method which has to be called before the context is destroyed.

IntializeDestroyExample

package com.javainterviewconcept;

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

public class InitializeDestroyExample
{
    @PostConstruct
    public void initializationMethod()
    {
        System.out.println("Initialization method called");
    }
    
    public void display()
    {
        System.out.println("Welcome to javainterviewconcept!!!");
    }
    @PreDestroy
    public void destroyMethod()
    {
        System.out.println("Destroy method called");
    }
}