Bena's life cycle

Bean's Lifecycle

• • • Prepare to create
    • Create instantiation
    • Dependency Injection
    • Container cache
    • Destroy the instance

The life cycle of a bean can be divided into five stages, namely preparation before creation, creation and instantiation, dependency injection, container cache, and instance destruction.

Preparation before creation
The main function of this stage is to parse and find Bean-related extension implementations from the context and some configurations before the Bean starts to load.For example, like init-method, a method that the container will call when initializing a bean; destroy-method, a method that the container will call when destroying a bean; and BeanFactoryPostProcessor(), an extension class method provided by spring.Some pre- and post-processing extensions in this type of bean loading process are implemented. These classes or configurations are actually provided by Spring for us to implement some extensions in the bean loading process. In the middle of many integrations with Springitems are also relatively common.

Create instantiation
The second stage is to create an instance. The main function of this stage is to create an instance object of the Bean through reflection.And will scan and parse some properties of the Bean name.When this step is completed, the Bean object has been created, but the Spring Bean is not used externally.

Dependency injection
The third stage is the dependency injection stage. If the instantiated bean depends on other beans, object injection needs to be performed on these dependent beans.For example, some configuration forms such as common @Autowired annotation injection or setter() injection in xml files.At the same time, some extension calls will be triggered at this stage, for example, the common extension class BeanPostProcessors post-processor is used to implement extension callbacks before and after Bean initialization, as well as BeanFactoryAware, etc.

Container cache
The fourth stage is the container cache stage. The main function of this stage is to save the beans in the container and Spring's cache.At this stage, the Bean can actually be called by the developer.The operations involved in this stage are common such as init-method, some methods configured by this property will be called in this stage; and post-processor methods like BeanPostProcessoes will also be triggered in this stage.

Destroy the instance
The fifth stage is to destroy the instance. When the Spring application context is closed, all the beans in the context will be destroyed. If there is a bean configurationThese methods of destroy-method will be called at this stage.