SpringBoot—@EnableAutoConfiguration注解的分析-优快云博客

本文链接：https://blog.youkuaiyun.com/m0_63330888/article/details/127646592

第一部分@EnableAutoConfiguration

1.1作用：

通过扫描Classpath下的spring.fatories配置文件，将org.springframework.boot.autoconfig.EnableAutoConfiguration对应的配置项实例化且注入到spring容器；

1.2实现原理—流程分析

1.2.1 进入@EnableAutoConfiguration注解，主要由两个注解组成：

@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)

springboot之所以能自动注入应用程序所需要的bean，靠的就是@import注解，继续向下走，

1.2.2 进入AutoConfigurationImportSelector类

类中有方法selectImports()，调用了getAutoConfigurationEntry()方法；

1.2.3 进入selectImports

1.2.4 进入getAutoConfigurationEntry()方法

此时debug发现，

configurations集合已经有很多的类的全限定名了，注意返回的是list集合；接着继续跟踪getCandidateConfigurations()；

1.2.5 进入getCandidateConfigurations()方法

1.2.6 继续跟踪loadFactoryNames()

这个时候我发现calssloader类加载器对象实例作为形参传入了loadSpringFactories()

1.2.7 进入loadSpringFactories()

重点，在次方法完成了对spring.fatories配置文件配置的获取。（建议分析每一行）

	private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) {
		Map<String, List<String>> result = cache.get(classLoader);
		if (result != null) {
			return result;
		}

		result = new HashMap<>();
		try {
        //获取spring.properites配置文件里类的全限定名
		Enumeration<URL> urls = classLoader.getResources(FACTORIES_RESOURCE_LOCATION);
        
			while (urls.hasMoreElements()) {
				URL url = urls.nextElement();
				UrlResource resource = new UrlResource(url);
        //PropertiesLoaderUtils，这个工具类主要是针对Properties文件的加载操作，在Spring    //对.properties文件和.factories文件的操作都有使用到。loadProperties:从一个资源文件加载    //Properties；
				Properties properties = PropertiesLoaderUtils.loadProperties(resource);
				for (Map.Entry<?, ?> entry : properties.entrySet()) {
        //获取到properties中的key值
					String factoryTypeName = ((String) entry.getKey()).trim();
        //获取到value值
					String[] factoryImplementationNames =
							StringUtils.commaDelimitedListToStringArray((String) entry.getValue());
        //遍历所有的value。
					for (String factoryImplementationName : factoryImplementationNames) {
						result.computeIfAbsent(factoryTypeName, key -> new ArrayList<>())
								.add(factoryImplementationName.trim());
					}
				}
			}

			// Replace all lists with unmodifiable lists containing unique elements
			result.replaceAll((factoryType, implementations) -> implementations.stream().distinct()
					.collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList)));
			cache.put(classLoader, result);
		}
		catch (IOException ex) {
			throw new IllegalArgumentException("Unable to load factories from location [" +
					FACTORIES_RESOURCE_LOCATION + "]", ex);
		}
		return result;
	}

从spring.peoperties获取的url（145行）: jar:file:/D:/repository/org/springframework/boot/spring-boot-actuator-autoconfigure/2.5.14/spring-boot-actuator-autoconfigure-2.5.14.jar!/META-INF/spring.factories

根据url获取的resource(146行):

URL [jar:file:/D:/repository/org/springframework/boot/spring-boot-actuator-autoconfigure/2.5.14/spring-boot-actuator-autoconfigure-2.5.14.jar!/META-INF/spring.factories]

-----------------------------------------------------start---------------------------------------------------------------

使用 PropertiesLoaderUtils.loadProperties(resource)获取到的properties对象有三个

看着多，其实就是做个参考，后面是循环读的值，箭头坐为key,右侧为对应的value,

这个代表着从spring.properties获取到的资源，也是自动导入所能导入的全部资源，都在这了！！！
org.springframework.boot.diagnostics.FailureAnalyzer -> org.springframework.boot.actuate.autoconfigure.metrics.ValidationFailureAnalyzer
-------------------------------------------------------------------------------------------
org.springframework.boot.actuate.autoconfigure.web.ManagementContextConfiguration -> org.springframework.boot.actuate.autoconfigure.endpoint.web.ServletEndpointManagementContextConfiguration,

org.springframework.boot.actuate.autoconfigure.endpoint.web.reactive.WebFluxEndpointManagementContextConfiguration,

org.springframework.boot.actuate.autoconfigure.endpoint.web.servlet.WebMvcEndpointManagementContextConfiguration,org.springframework.boot.actuate.autoconfigure.endpoint.web.jersey.JerseyWebEndpointManagementContextConfiguration,org.springframework.boot.actuate.autoconfigure.security.servlet.SecurityRequestMatchersManagementContextConfiguration,org.springframework.boot.actuate.autoconfigure.web.jersey.JerseySameManagementContextConfiguration,org.springframework.boot.actuate.autoconfigure.web.jersey.JerseyChildManagementContextConfiguration,org.springframework.boot.actuate.autoconfigure.web.reactive.ReactiveManagementChildContextConfiguration,org.springframework.boot.actuate.autoconfigure.web.servlet.ServletManagementChildContextConfiguration,org.springframework.boot.actuate.
----------------------------------------------------------------------------------------
org.springframework.boot.autoconfigure.EnableAutoConfiguration -> org.springframework.boot.actuate.autoconfigure.amqp.RabbitHealthContributorAutoConfiguration,

org.springframework.boot.actuate.autoconfigure.audit.AuditAutoConfiguration,

org.springframework.boot.actuate.autoconfigure.audit.AuditEventsEndpointAutoConfiguration,org.springframework.boot.actuate.autoconfigure.availability.AvailabilityHealthContributorAutoConfiguration,org.springframework.boot.actuate.autoconfigure.availability.AvailabilityProbesAutoConfiguration,org.springframework.boot.actuate.autoconfigure.beans.BeansEndpointAutoConfiguration,org.springframework.boot.actuate.autoconfigure.cache.CachesEndpointAutoConfiguration,org.springframework.boot.actuate.autoconfigure.cassandra.CassandraHealthContributorAutoConfiguration,org.springframework.boot.actuate.autoconfigure.cassandra.CassandraReactiveHealthContributorAutoConfiguration,org.springframework.boot.actuate.autoconfigure.cloudfoundry.servlet.CloudFoundryActuatorAutoConfiguration,org.springframework.boot.actuate.autoconfigure.cloudfoundr

-----------------------------------------------------------end---------------------------------------------------------

/*

https://www.jianshu.com/p/059d6e908807（computeIfAbsent()具体的讲解）
hashMap.computeIfAbsent("china", key -> getValues(key)).add("liSi");

如果原来有china 的key值，源码的方法是生成一个动态数组，相同key的放入数组中

如果原来没有china key，则会生成新的key：value china=xxx;
*/

/*

使用Spring PropertiesLoaderUtils读取properties属性文件_青山青的博客-优快云博客_propertiesloaderutils读取配置文件 PropertiesLoaderUtils.loadProperties(resource)方法的具体使用👆

*/

注意：返回的HashMap中的key:我们发现146行获取的resource是url路径对吧，

147行loadProperties()方法对spring.properties配置文件进行加载！注意就是这里，我们慢慢看。

1.3debug（重要）

了解各个引用含义，梳理逻辑，非常重要。源码只能去理解代码，而不要心存质疑，眼见即接受。

resource:

URL [jar:file:/D:/repository/org/springframework/cloud/spring-cloud-stream-binder-rabbit/3.1.6/spring-cloud-stream-binder-rabbit-3.1.6.jar!/META-INF/spring.factories]

➡147行:properties:

通过加载spring.properties配置文件得到的是key:org.springframework.boot.autoconfigure.EnableAutoConfiguration

value:org.springframework.cloud.stream.binder.rabbit.config.ExtendedBindingHandlerMappingsProviderConfiguration

现在，就得到了Properties EnableAutoConfiguration 对象,

➡148行：就是对Properties对象进行遍历，得到key,

➡149行:factoryTypeName:就是key值org.springframework.boot.autoconfigure.EnableAutoConfiguration

➡150行:factoryImplementationNames:就是value值,org.springframework.cloud.stream.binder.rabbit.config.ExtendedBindingHandlerMappingsProviderConfiguration

➡152行:遍历的是org.springframework.cloud.stream.binder.rabbit.config.ExtendedBindingHandlerMappingsProviderConfiguration

➡153行:result

我们发现result首先是一个HashMap,他的key有三个，每个都对应着不同数量的value,

此时，我们的
factoryImplementationName为org.springframework.cloud.stream.binder.rabbit.config.ExtendedBindingHandlerMappingsProviderConfiguration
result的key为三个如图所示；俩值不一致，那么方法就会将org.springframework.cloud.stream.binder.rabbit.config.ExtendedBindingHandlerMappingsProviderConfiguration放入result;结束本次循环

144行while再次循环开始，再次从spring.properties读取资源，引用名字为properties,读取到的值为：org.springframework.boot.env.EnvironmentPostProcessor -> org.springframework.cloud.stream.function.RoutingFunctionEnvironmentPostProcessor

key = "org.springframework.boot.env.EnvironmentPostProcessor"
value = "org.springframework.cloud.stream.function.RoutingFunctionEnvironmentPostProcessor"

---------------------------------------------------------------------------------------------------------------------

org.springframework.boot.autoconfigure.EnableAutoConfiguration -> org.springframework.cloud.stream.config.ChannelBindingAutoConfiguration,org.springframework.cloud.stream.config.BindersHealthIndicatorAutoConfiguration,org.springframework.cloud.stream.config.ChannelsEndpointAutoConfiguration,org.springframework.cloud.stream.config.BindingsEndpointAutoConfiguration,org.springframework.cloud.stream.config.BindingServiceConfiguration,org.springframework.cloud.stream.function.FunctionConfiguration

key = "org.springframework.boot.autoconfigure.EnableAutoConfiguration"
value = "org.springframework.cloud.stream.config.ChannelBindingAutoConfiguration,org.springframework.cloud.stream.config.BindersHealthIndicatorAutoConfiguration,org.springframework.cloud.stream.config.ChannelsEndpointAutoConfiguration,org.springframework.cloud.stream.config.BindingsEndpointAutoConfiguration,org.springframework.cloud.stream.config.BindingServiceConfiguration,org.springframework.cloud.stream.function.FunctionConfiguration"

那么这个时候呢，149行的key:factoryTypeName和150行的value:factoryImplementationNames分别为
key = "org.springframework.boot.env.EnvironmentPostProcessor"
value = "org.springframework.cloud.stream.function.RoutingFunctionEnvironmentPostProcessor"

这个时候，会再次向result中存value,result也就变成了4条数据！！！

然后就是下一次的循环。。

最终结果为：28条，EnableAutoConfiguration一条内就有300条

debug参照方法源码👇

1.4返回

最后，1.返回HashMap类型的result至loadFactoryNames（）方法

public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
		ClassLoader classLoaderToUse = classLoader;
		if (classLoaderToUse == null) {
			classLoaderToUse = SpringFactoriesLoader.class.getClassLoader();
		}
		String factoryTypeName = factoryType.getName();
		return loadSpringFactories(classLoaderToUse).getOrDefault(factoryTypeName, Collections.emptyList());
	}

return loadSpringFactories(classLoaderToUse).getOrDefault(factoryTypeName, Collections.emptyList());

getOrDefault() 方法获取指定 key 对应对 value，如果找不到 key ，则返回设置的默认值。getOrDefault() 方法的语法为：hashmap.getOrDefault(Object key, V defaultValue)

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
		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.");
		return configurations;
	}

读取到的confurgations的值

3.getAutoConfigurationEntry

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);
	}

4.selectImports()

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

结束，整个流程就是这样。那么我发现的是在loadSpringFactories()方法完成了对资源的获取，最终是List<String>格式返回至AutoConfigurationImportSelector 类的getAutoConfigurationEntry方法结束，@import注解也就是这样将我们所需要的资源完成了查找并且注入IOC容器中！