spring boot （一）-优快云博客

本文深入解析SpringBoot启动注解@SpringBootApplication的工作机制，详细介绍了@EnableAutoConfiguration如何实现自动装配，以及AutoConfigurationImportSelector类如何通过SpringFactoriesLoader加载并解析META-INF/spring.factories文件，最终确定自动配置类。

spring boot 启动注解 @SpringBootApplication

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration  //继承了Configuration，表示当前是注解类
@EnableAutoConfiguration  //自动装配注解
@ComponentScan(excludeFilters = {  //扫描包设置
		@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM,
				classes = AutoConfigurationExcludeFilter.class) })  
public @interface SpringBootApplication {

重点 @EnableAutoConfiguration spring boot 自动装配注解

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)  //导入自动配置的组件
public @interface EnableAutoConfiguration {

再看AutoConfigurationImportSelector.class 类重要方法 String [] selectImports 获取自动装配全限定类名数组

@Override
	public String[] selectImports(AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return NO_IMPORTS;
		}
		AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
				.loadMetadata(this.beanClassLoader);
         //方法调用
		AutoConfigurationEntry autoConfigurationEntry = getAutoConfigurationEntry(
				autoConfigurationMetadata, annotationMetadata);
		return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations());
	}


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

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,
			AnnotationAttributes attributes) {
        //自动配置幕后英雄：SpringFactoriesLoader   其主要功能就是从指定的配置文件META-                INF/spring.factories加载配置
		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;
	}

调用SpringFactoriesLoader 类方法

public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
        String factoryClassName = factoryClass.getName();
        return (List)loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
    }

    private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
        MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);
        if (result != null) {
            return result;
        } else {
            try {
                Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
                //////
            } catch (IOException var13) {
                throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);
            }
        }
    }

可见最后由 SpringFactoriesLoader将META-INF/spring.factories 文件加载解析

spring-boot-autoconfigure下的spring.factory文件大部分配置类都是spring boot 启动配置类

在看看比如spring-cloud-netflix-ribbon 中的spring.factory 只有一个RibbonAutoConfiguration

再看下RibbonAutoConfiguration类

@Configuration  //说明是一个配置类
@Conditional(RibbonAutoConfiguration.RibbonClassesConditions.class)   //装配条件  只有classpath存在指定类才加载
@RibbonClients
@AutoConfigureAfter(name =  //加载配置顺序在XX之后 "org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration")
@AutoConfigureBefore({ LoadBalancerAutoConfiguration.class,
		AsyncLoadBalancerAutoConfiguration.class })
@EnableConfigurationProperties({ RibbonEagerLoadProperties.class,
		ServerIntrospectorProperties.class })   //自动转化properties文件配置
public class RibbonAutoConfiguration {

spring boot 默认配置查看