Life Cycle Management of a Spring Bean

1) Introduction

This article would brief about how a Spring Bean is managed in IOC (Inversion of Control) Container. Spring Beans exist within the Container as long as they are needed by the Appplication. There are various life-cycle interfaces and methods that will be called by the IOC Container. The pre-requisite for this article is some basic knowledge in Spring which can be got by reading the article in javabeat Introduction to Spring Web Framework.

2) Bean Life Cycle

A Spring Bean represents a POJO component performing some useful operation. All Spring Beans reside within a Spring Container also known as IOC Container. The Spring Framework is transparent and thereby hides most of the complex infrastructure and the communication that happens between the Spring Container and the Spring Beans. This section lists the sequence of activities that will take place between the time of Bean Instantiation and hand over of the Bean reference to the Client Application.

1. The Bean Container finds the definition of the Spring Bean in the Configuration file.
2. The Bean Container creates an instance of the Bean using Java Reflection API.
3. If any properties are mentioned, then they are also applied. If the property itself is a Bean, then it is resolved and set.
4. If the Bean class implements the BeanNameAware interface, then the setBeanName() method will be called by passing the name of the Bean.
5. If the Bean class implements the BeanClassLoaderAware interface, then the method setBeanClassLoader() method will be called by passing an instance of the ClassLoader object that loaded this bean.
6. If the Bean class implements the BeanFactoryAware interface, then the method setBeanFactory() will be called by passing an instance of BeanFactory object.
7. If there are any BeanPostProcessors object associated with the BeanFactory that loaded the Bean, then the method postProcessBeforeInitialization() will be called even before the properties for the Bean are set.
8. If the Bean class implements the InitializingBean interface, then the method afterPropertiesSet() will be called once all the Bean properties defined in the Configuration file are set.
9. If the Bean definition in the Configuration file contains a 'init-method' attribute, then the value for the attribute will be resolved to a method name in the Bean class and that method will be called.
10. The postProcessAfterInitialization() method will be called if there are any Bean Post Processors attached for the Bean Factory object.
11. If the Bean class implements the DisposableBean interface, then the method destroy() will be called when the Application no longer needs the bean reference.
12. If the Bean definition in the Configuration file contains a 'destroy-method' attribute, then the corresponding method definition in the Bean class will be called.