Spring Boot自动装配原理

@Inherited@SpringBootConfiguration@EnableAutoConfiguration// 自动装配原理的核心注解@ComponentScan(excludeFilters= { @Filter(type=FilterType.CUSTOM, classes=TypeExcludeFilter.class),
@Filter(type=FilterType.CUSTOM, classes=AutoConfigurationExcludeFilter.class) })
public@interfaceSpringBootApplication {

@Inherited@AutoConfigurationPackage/*** 自动装配的时候使用的是@Import注解* 作用是导入一个或者多个组件搭配@Configuration注解使用，交给spring容器管理* 该注解有三种方式* 1.@import：指定导入一个或者多个类* 2.ImportSelector：定义一个类实现该接口，重写selectImports方法* 3.* 扩展：@ImportResource：指定导入一个或者多个xml文件*/@Import(AutoConfigurationImportSelector.class)
public@interfaceEnableAutoConfiguration {

// 重写来自于DeferredImportSelector.Group#process@Overridepublicvoidprocess(AnnotationMetadataannotationMetadata, DeferredImportSelectordeferredImportSelector) {
Assert.state(deferredImportSelectorinstanceofAutoConfigurationImportSelector,
                 () ->String.format("Only %s implementations are supported, got %s",
AutoConfigurationImportSelector.class.getSimpleName(),
deferredImportSelector.getClass().getName()));
// 获取自动装配信息AutoConfigurationEntryautoConfigurationEntry= ((AutoConfigurationImportSelector) deferredImportSelector)
        .getAutoConfigurationEntry(annotationMetadata);
this.autoConfigurationEntries.add(autoConfigurationEntry);
for (StringimportClassName : autoConfigurationEntry.getConfigurations()) {
this.entries.putIfAbsent(importClassName, annotationMetadata);
    }
}
// 获取自动装配信息protectedAutoConfigurationEntrygetAutoConfigurationEntry(AnnotationMetadataannotationMetadata) {
if (!isEnabled(annotationMetadata)) {
returnEMPTY_ENTRY;
    }
AnnotationAttributesattributes=getAttributes(annotationMetadata);
// 加载所有在META-INF/spring.factories中配置的类 跳到①List<String>configurations=getCandidateConfigurations(annotationMetadata, attributes);
configurations=removeDuplicates(configurations);
Set<String>exclusions=getExclusions(annotationMetadata, attributes);
checkExcludedClasses(configurations, exclusions);
configurations.removeAll(exclusions);
// 经过condition注解过滤后的自动配置类configurations=getConfigurationClassFilter().filter(configurations);
fireAutoConfigurationImportEvents(configurations, exclusions);
returnnewAutoConfigurationEntry(configurations, exclusions);
}
// ① META-INF/spring.factories中读取所有的候选的自动配置类名称protectedList<String>getCandidateConfigurations(AnnotationMetadatametadata, AnnotationAttributesattributes) {
// 通过SpringFactoriesLoader读取所有的候选的自动配置类名称// ② 加载配置候选的类List<String>configurations=SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
getBeanClassLoader());
Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you "+"are using a custom packaging, make sure that file is correct.");
returnconfigurations;
}
// ③ 加载配置候选的类protectedClass<?>getSpringFactoriesLoaderFactoryClass() {
returnEnableAutoConfiguration.class;
}
// 所以如果想要将一个外部（第三方）的类交给spring容器管理，可以把这个类配置添加到META-INF/spring.factories文件中。// 例如自定义starter场景启动器

// ImportSelector （重要！SpringBoot底层使用这种方式，但是又有区别）publicclassMyImportSelectorimplementsImportSelector {
@OverridepublicString[] selectImports(AnnotationMetadataimportingClassMetadata) {
// 返回值String[]中值依旧是要导入类的全限定名，注意，返回值可以是空数组但是不能为nullreturnnewString[]{"com.fun.bootdemo.custome.Demo1"};
    }
}
/*** SpringBoot底层使用的是：* org.springframework.boot.autoconfigure.AutoConfigurationImportSelector* 该类实现的是DeferredImportSelector接口，该接口包含有额外功能：* gruop 该分组可以用来进行排序和过滤时同时DeferredImportSelector是优先级比较低的，* 需要等到其他bean注册完了。才注册该接口导入的bean。这个功能很好的结合了@Conditon等条件注解* 实现了用户自定义配置覆盖默认配置*/// ImportBeanDefinitionRegistrarpublicclassMyImportBeanDefinitionRegistrarimplementsImportBeanDefinitionRegistrar {
@OverridepublicvoidregisterBeanDefinitions(AnnotationMetadataimportingClassMetadata, BeanDefinitionRegistryregistry) {
// 指定注册bean定义信息RootBeanDefinitionrootBeanDefinition=newRootBeanDefinition(Demo3.class);
// demo3 是beanNameregistry.registerBeanDefinition("demo3", rootBeanDefinition);
    }
}
// 测试 （在配置类上）@Import({MyImportSelector.class, MyImportBeanDefinitionRegistrar.class})