Bean Lifecycle

1. Process

• Instantiate the Bean.
• Inject values and references into the Bean’s corresponding properties.
• Inject Spring low-level components into the Bean through Aware interfaces.
• BeanPostProcessor: execute additional logic. It runs before and after InitializingBean, and the Bean currently being created is passed in.
• InitializingBean: execute additional logic, but the Bean currently being created is not passed in.
• DisposableBean: call the destroy method when the Bean is destroyed.

2. Usage

There are four approaches in total.

2.1. Specify init and destroy Methods with @Bean

public class BeanCycle
{
    public BeanCycle()
    {
        System.out.println("1. bean created");
    }

    public void init()
    {
        System.out.println("2. bean initialized");
    }

    public void destroy()
    {
        System.out.println("3. bean destroyed");
    }
}


@Bean(initMethod = "init", destroyMethod = "destroy")
public BeanCycle beanCycle()
{
    return new BeanCycle();
}

2.2. Implement InitializingBean and DisposableBean

@Component
@ComponentScan("com.example.context.bean")
public class BeanCycle2 implements InitializingBean, DisposableBean
{
    public BeanCycle2()
    {
        System.out.println("bean2 created");
    }


    @Override
    public void afterPropertiesSet() throws Exception
    {
        System.out.println("bean2 properties have been set");

    }

    @Override
    public void destroy() throws Exception
    {
        System.out.println("bean2 destroyed");

    }
}

2.3. Annotate Methods with @PostConstruct and @PreDestroy

2.4. Implement BeanPostProcessor

@Component
public class MyBeanPostProcessor implements BeanPostProcessor
{
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException
    {
        System.out.println("do some work before initialization");
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException
    {
        System.out.println("do some work after initialization");
        return bean;
    }
}

3. References

• Spring Bean Lifecycle (Very Detailed) - Chandler Qian - CNBlogs
• 1. Create the Spring Container