9，自动配置原理-优快云博客

本文链接：https://blog.youkuaiyun.com/lvshare/article/details/144696515

通过文章6，7，8大概就能知道Spring Boot的自动配置原理和Spring Boot重要核心-自动配置，

我们在pom中引入依赖，会自动注册一些类和方法到项目中，依据引入spring-boot-starter-web依赖，

启动类注解：

@SpringBootApplication

按CTRL—鼠标左键，进入注解类

@SpringBootConfiguration
@EnableAutoConfiguration

@SpringBootConfiguration包含：证明启动类也是一个配置类

@Configuration

@EnableAutoConfiguration包含：文章7中，我们用到过 ImportSelector 类，这个类会被Spring Boot 自动调用

@Import({AutoConfigurationImportSelector.class})

继续进入AutoConfigurationImportSelector 类中，实现 DeferredImportSelector 类

实现方法

public String[] selectImports(AnnotationMetadata annotationMetadata) {
    if (!this.isEnabled(annotationMetadata)) {
        return NO_IMPORTS;
    } else {
        AutoConfigurationImportSelector.AutoConfigurationEntry autoConfigurationEntry = this.getAutoConfigurationEntry(annotationMetadata);
        return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
    }
}

返回的结果集是：autoConfigurationEntry.getConfigurations()

结果集是从：this.getAutoConfigurationEntry(annotationMetadata)这个方法来，进入方法

protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
   if (!isEnabled(annotationMetadata)) {
      return EMPTY_ENTRY;
   }
   AnnotationAttributes attributes = getAttributes(annotationMetadata);
   List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
   configurations = removeDuplicates(configurations);
   Set<String> exclusions = getExclusions(annotationMetadata, attributes);
   checkExcludedClasses(configurations, exclusions);
   configurations.removeAll(exclusions);
   configurations = getConfigurationClassFilter().filter(configurations);
   fireAutoConfigurationImportEvents(configurations, exclusions);
   return new AutoConfigurationEntry(configurations, exclusions);
}

而返回的类里，configurations是通过getCandidateConfigurations(annotationMetadata, attributes)方法，再继续进入方法

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
   ImportCandidates importCandidates = ImportCandidates.load(this.autoConfigurationAnnotation,
         getBeanClassLoader());
   List<String> configurations = importCandidates.getCandidates();
   Assert.notEmpty(configurations,
         "No auto configuration classes found in " + "META-INF/spring/"
               + this.autoConfigurationAnnotation.getName() + ".imports. If you "
               + "are using a custom packaging, make sure that file is correct.");
   return configurations;
}

这个类就已经能看到，和我们在第七章中的配置文件加载类方法相同了，打断点测试，能看到this.autoConfigurationAnnotation，这个路径值