java - @Autowired在Spring中是如何实现的

Question

我真的很想对@autowired 有一个基本的了解在 Spring 中实现。
反射应该以某种方式隐含在它的实现中，但我不知道如何。
你能帮我吗 ？

Answer 1

通过@Autowired 的 Autowiring 由BeanPostProcessor 实现执行，特别是org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor .

此 BeanPostProcessor 处理每个 bean，将扫描其类(和父类(super class))以查找任何 @Autowired 注释，并且根据注释是什么(构造函数、字段、或方法)，它将采取适当的行动。

对于构造函数

Only one constructor (at max) of any given bean class may carry this annotation with the 'required' parameter set to true, indicating the constructor to autowire when used as a Spring bean. If multiple non-required constructors carry the annotation, they will be considered as candidates for autowiring. The constructor with the greatest number of dependencies that can be satisfied by matching beans in the Spring container will be chosen. If none of the candidates can be satisfied, then a default constructor (if present) will be used. An annotated constructor does not have to be public.

对于字段

Fields are injected right after construction of a bean, before any config methods are invoked. Such a config field does not have to be public.

对于方法

Config methods may have an arbitrary name and any number of arguments; each of those arguments will be autowired with a matching bean in the Spring container. Bean property setter methods are effectively just a special case of such a general config method. Config methods do not have to be public.

所有这些都是通过反射完成的。

进一步阅读:

• How do I invoke a Java method when given the method name as a string?
• Is it possible in Java to access private fields via reflection