Java注解@Autowired的工作原理 JavaSAPSAP云平台SAP Cloud PlatformSpring
Suppose I have a bean named HelloWorld which has a member attribute points to another bean User.
With annotation @Autowired, as long as getBean is called in the runtime, the returned HelloWorld instance will automatically have user attribute injected with User instance.
How is this behavior implemented by Spring framework? (1) in Spring container implementation’s refresh method, all singleton beans will be initialized by default.
When the HelloWorld bean is initialized:
Since it has the following source code:
@Autowired private User user; In the runtime, this annotation is available in metadata via reflection. In metadata structure below, the targetClass points to HelloWorld bean, and injectedElements points to the User class to be injected.
(2) In doResolveDependency, the definition for User bean is searched based on this.beanDefinitionNames ( list in DefaultListableBeanFactory ):
Once found, the found result is added to array candidateNames:
Then the constructor of User bean class is called ( still triggered by getBean call ), the user instance is created by calling constructor:
The created user instance together with its name “user” is inserted to the map matchingBeans.
(3) Finally the user reference is set to user attribute of HelloWorld instance via reflection. Here the variable bean in line 569 points to HelloWorld instance, and value points to user instance.
Once field.set(bean, value) is done, we can observe in debugger that the user attribute in HelloWorld instance is already injected successfully.
要获取更多Jerry的原创文章,请关注公众号"汪子熙":
推荐阅读
-
JUnit 注解@RunWith的工作原理 JUNITJavaSAPSAP云平台SAP Cloud Platform
-
Java注解@Autowired的工作原理 JavaSAPSAP云平台SAP Cloud PlatformSpring
-
Java注解@Cacheable的工作原理 Java@cacheSAPSAP云平台SAP Cloud Platform
-
Java Volatile的一个实际应用场合 JavaSAPSAP云平台SAP Cloud PlatformCloud
-
Java注解@Cacheable的工作原理 Java@cacheSAPSAP云平台SAP Cloud Platform
-
JUnit 注解@RunWith的工作原理 JUNITJavaSAPSAP云平台SAP Cloud Platform
-
JUnit 注解@SuiteClasses的工作原理 JUNITSAPSAP云平台SAP Cloud PlatformSAP成都研究院
-
JUnit 注解@Rule的工作原理 junitSAPSAP云平台JavaSAP Cloud Platform
-
JUnit 注解@Category的工作原理 junitjavaSAPSAP云平台SAP Cloud Platform
-
Java注解@Autowired的工作原理 JavaSAPSAP云平台SAP Cloud PlatformSpring