Spring Bean Lifecycle with Executable Code

Lifecycle code example

@Component
public class LifeCycleDemoBean implements 
        InitializingBean, 
        DisposableBean, 
        BeanNameAware,
        BeanFactoryAware, 
        ApplicationContextAware {


    public LifeCycleDemoBean() {
        System.out.println("## 1. I'm in the LifeCycleBean Constructor");
    }

    /**
     * {@link BeanNameAware}
     */
    @Override
    public void setBeanName(String name) {
        System.out.println("## 2. My Bean Name is: " + name);
    }

    /**
     * {@link BeanFactoryAware}
     */
    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        System.out.println("## 3. Bean Factory has been set");
    }

    /**
     * {@link ApplicationContextAware}
     */
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        System.out.println("## 4. Application context has been set");
    }

    /**
     * {@link LifeCycleDemoBeanPostProcessor}
     */
    public void beforeInit(){
        System.out.println("## 5. Before Init - Called by BeanPostProcessor: LifeCycleDemoBeanPostProcessor");
    }

    @PostConstruct
    public void postConstruct(){
        System.out.println("## 6. The Post Construct annotated method has been called");
    }

    /**
     * {@link InitializingBean}
     */
    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("## 7. The LifeCycleBean has its properties set!");
    }

    /**
     * {@link LifeCycleDemoBeanPostProcessor}
     */
    public void afterInit(){
        System.out.println("## 8. After init: called by BeanPostProcessor: LifeCycleDemoBeanPostProcessor");
    }

    @PreDestroy
    public void preDestroy() {
        System.out.println("## 9. The PreDestroy annotated method has been called");
    }

    /**
     * {@link DisposableBean}
     */
    @Override
    public void destroy() throws Exception {
        System.out.println("## 10. The Lifecycle bean has been terminated");
    }
}

Run the application and then stop it, the printed messages would show in console in the order as their number marks, which is exactly the same as lifecycle image shows:

// run the application
## 1. I'm in the LifeCycleBean Constructor
## 2. My Bean Name is: lifeCycleDemoBean
## 3. Bean Factory has been set
## 4. Application context has been set
## 5. Before Init - Called by BeanPostProcessor: LifeCycleDemoBeanPostProcessor
## 6. The Post Construct annotated method has been called
## 7. The LifeCycleBean has its properties set!
## 8. After init: called by BeanPostProcessor: LifeCycleDemoBeanPostProcessor

// stop the application
## 9. The PreDestroy annotated method has been called
## 10. The Lifecycle bean has been terminated

BeanPostProcessor:

Note that in the above example, the method beforeInit and afterInit are achieved by implement BeanPostProcessor. BeanPostProcessor give us hooks into the Spring bean lifecycle to modify its configuration.

@Component
public class LifeCycleDemoBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {

        if(bean instanceof LifeCycleDemoBean){
            ((LifeCycleDemoBean) bean).beforeInit();
        }

        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if(bean instanceof LifeCycleDemoBean){
            ((LifeCycleDemoBean) bean).afterInit();
        }

        return bean;
    }
}