@ Autowired annotation of Spring

Java code
@ Retention (RetentionPolicy. RUNTIME)
@ Target ({ElementType. CONSTRUCTOR, ElementType. FIELD, ElementType. METHOD })
Public @ interface Autowired {

/**
* Declares whether the annotated dependency is required.
* <P> Defaults to <code> true </code>.
*/
Boolean required () default true;

}

@ Retention (RetentionPolicy. RUNTIME)
@ Target ({ElementType. CONSTRUCTOR, ElementType. FIELD, ElementType. METHOD })
Public @ interface Autowired {

/**
* Declares whether the annotated dependency is required.
* <P> Defaults to <code> true </code>.
*/
Boolean required () default true;

} We know from the source code that it is an annotation interface of spring and there is a method.

 

Java code
Boolean required () default true;

Boolean required () default true;

The following conditions must be met:

1. The spring configuration file must be added with something that can recognize annotations.

Org. springframework. beans. factory. annotation. AutowiredAnnotationBeanPostProcessor

Or use xml to mark the following (note the version)

Xmlns: context

<Context: component-scan base-package = "org. javaeye. *"/>

Four annotations are supported: @ Component, @ Serivce, @ Controller, and @ Repository.

@ Controller: Control Layer

@ Serivce: business logic layer

@ Repository: Persistence Layer

2. Annotations exist.

 

 

Java code
@ Autowired
UserService userService;

@ Autowired
UserService userService; 3. Corresponding setter Method

 

Java code
Public void setUserService (UserService userService ){
This. userService = userService;
}

Public void setUserService (UserService userService ){
This. userService = userService;
} 4. If it is an interface or an abstract class, the class must be unique; otherwise, an error occurred while creating the instance.

 

Java code
Org. springframework. beans. factory. NoSuchBeanDefinitionException:
No unique bean of type
[Com. sohu. suc. splatform. service. UserService] is defined:
Expected single matching bean but found 2:
[UserServiceHibernateImpl, userServiceImp]

Org. springframework. beans. factory. NoSuchBeanDefinitionException:
No unique bean of type
[Com. sohu. suc. splatform. service. UserService] is defined:
Expected single matching bean but found 2:
[UserServiceHibernateImpl, userServiceImp]
5. The implementation of interfaces must be known to spring, and spring needs to be aware of them by bean configuration or annotation.

 

Java code
@ Service
Public class UserServiceImpl implements UserService {
.......
}

@ Service
Public class UserServiceImpl implements UserService {
.......
} In summary, spring only manages the bean he knows. There are two ways to let spring know the existence of bean.

1. annotation Method

2. bean Configuration