Spring Bean Life Cycle by R4R Team

Spring Bean Life Cycle:-
The most important feature of Spring is the bean based approach. The Spring bean is created, managed and dispensed by the Spring IoC container. Each Spring bean has a lifecycle and understanding the spring bean lifecycle enables better coding.
The life cycle of a Spring bean is very easy to understand. When a bean is instantiated, it may be required to perform some initialization to get it into a usable state.The following are the stages in a beanís   lifecycle.

Archetecture of Spring Bean Life Cycle:


1 Instantiate - The Spring container instantiates the bean.

2 Populate properties- Spring IoC container injects the beanís properties.

3 Set Bean Name- Spring container sets the bean name. If the bean implements BeanNameAware, spring container passes the beanís id to setBeanName() method.

4 Set Bean Factory-If the bean implements BeanFactoryAware, Spring container passes theBeanFactory to setBeanFactory().

5 Pre Initialization-This stage is also called the bean postprocess . If there are anyBeanPostProcessors, theSpring container calls the postProcesserBeforeInitialization () method.

6 Initialize beans- If the bean implements IntializingBean,its afterPropertySet()method is called. If the bean has init method declaration, the specified initialization method is called.

7 Post Initialization- IfBeanPostProcessors is implemented by the bean, the Spring container calls their postProcessAfterinitalization() method.

8 Ready to Use- Now the bean is ready to be used by the application.

9 Destroy- The bean is destroyed during this stage. If the bean implements DisposableBean, the Spring IoC container will call the destroy() method . If a custom destroy () method is defined, the container calls the specified method.


InitializingBean and DisposableBean callback interfaces:-
Initialization callbacks:
The org.springframework.beans.factory.InitializingBean interface allows a bean to perform initialization work after all necessary properties on the bean have been set by the container. The InitializingBean interface specifies a single method:
1 Single method
void afterPropertiesSet() throws Exception;

So you can simply implement above interface and initialization work can be done inside afterPropertiesSet() method as follows:

2 afterPropertiesSet() method

public class Bean implements InitializingBean {
public void afterPropertiesSet() {
// perform some initialization work
} }

When using the XML-based configuration metadata, you can use the init-method attribute to specify the name of the method that has a return void, no argument method signature. The following is example.

3 Example
<bean id="Bean"
class="com.r4r.Test.Bean" init-method="init"/>

4 The Test class definition:
public class Bean {
public void init() {
// do some initialization work
} }


Destruction callbacks:
The org.springframework.beans.factory. DisposableBean interface specifies a single method:
5 Single method
void destroy() throws Exception;
So to enable a destroy callback, simply implement the above interface and finalization work can be done inside destroy() method as follows:

6 destroy()

public class Bean implements DisposableBean {
public void destroy() {
// do the work to be performed before bean destruction
} }

When using the XML-based configuration metadata, you can use the destroy-method attribute to specify the name of the method that has a return void, no argument method signature. The following is example.

7 example
<bean id="sampleBean"
class="com.r4r.Test.Bean" destroy-method="destroy"/>

8 The class definition
public class Test {
public void destroy() {
// do some destruction work
} } 

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