zoukankan      html  css  js  c++  java
  • Spring框架里注解@Autowired的工作原理

    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.

    1. 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":

  • 相关阅读:
    Linux中杀不死的进程
    SQL语句 不支持日语 韩语 泰国语等的解决办法
    很长时间没写,重新开始每天进步一点点
    c#使用access数据库时 模糊查询 like 通配符的写法
    每天进步一点点之找工作的心路历程
    每天进步一点点之工作前三天
    Ajax实现原理
    java动态代理的原理
    css定位机制总结
    迷宫,较为高效的C++代码 BFS实现
  • 原文地址:https://www.cnblogs.com/sap-jerry/p/12844909.html
Copyright © 2011-2022 走看看