源码级讲解SpringBoot自动装配原理

用户4540099439462

2023-03-15 62 阅读5分钟

SpringBoot 定义了一套接口规范，这套规范规定：SpringBoot 在启动时会扫描外部引用 jar 包中的META-INF/spring.factories文件，将文件中配置的类型信息加载到 Spring 容器，并执行类中定义的各种操作。对于外部 jar 来说，只需要按照 SpringBoot 定义的标准，就能将自己的功能装置进 SpringBoot。

没有 SpringBoot 的情况下，如果我们需要引入第三方依赖，需要手动配置，非常麻烦。但是，SpringBoot 中，我们直接引入一个 starter 即可。比如你想要在项目中使用 redis 的话，直接在项目中引入对应的 starter 即可。

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-redis</artifactId>
</dependency>
复制代码

引入 starter 之后，我们通过少量注解和一些简单的配置就能使用第三方组件提供的功能了。

总的来说：使用Spring Boot时，我们只需引入对应的Starters，Spring Boot启动时便会自动加载相关依赖，配置相应的初始化参数，以最快捷、简单的形式对第三方软件进行集成，这便是Spring Boot的自动配置功能。

二.自动装配的实现原理

自动装配的核心类是ConfigurationClassPostProcessor，此类是BeanFactoryPostProcessor的实现类，在Spring的refresh方法中会执行其postProcessBeanDefinitionRegistry()方法。我们重点分析一下processConfigBeanDefinitions方法的处理流程。

2.1.parse方法

parse方法中调用了processConfigurationClass()方法，然后调用到 doProcessConfigurationClass()方法。

doProcessConfigurationClass()方法里面逻辑复杂，我们在看的时候先梳理清楚它主要做了什么，把功能拆解成多个子功能，然后再对单个子功能进行分析。

方法拆解后，会依次调用下面的方法：

那这些方法到底是做了些什么呢，下面我们就看下流程图：

2.processDeferredImportSelectors方法：

processDeferredImportSelectors代码截图百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度百度