SpringBoot的主动拆卸是拆箱即用的根底，也是为服务化的前提。
一、主动拆卸的过程
1.1 @SpringBootApplication
后面一章我解说过了《SpringBoot进阶之道-@SpringBootApplication》。咱们晓得@SpringBootApplication蕴含了@SpringBootConfiguration，@EnableAutoConfiguration，@ComponentScan。
1.2 @EnableAutoConfiguration
在上一章我解说过《SpringBoot进阶之道-@Enable模块驱动》，这种@Enabelxx的注解是开启某一项性能的注解，其原理是借助@Import，将所有合乎主动配置条件的bean定义加载到IOC容器。具体的能够去看看。
那么@EnableAutoConfiguration这个注解会开启springboot主动拆卸性能。直白的说，Spring会试图在你的classpath下找到所有配置的Bean而后进行拆卸。咱们以springboot2.x源码为例：
@Target({ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@AutoConfigurationPackage@Import({AutoConfigurationImportSelector.class})public @interface EnableAutoConfiguration { String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration"; Class<?>[] exclude() default {}; String[] excludeName() default {};}从源码咱们得悉，要害是@Import({AutoConfigurationImportSelector.class})，借助AutoConfigurationImportSelector，@EnableAutoConfiguration能够帮忙springboot利用将所有符合条件的@Configuration配置都加载到以后SpringBoot创立并应用的ioc容器。那么我为什么这么说呢？咱们看下AutoConfigurationImportSelector源码：
public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered { ... public AutoConfigurationImportSelector() { }}该类实现了DeferredImportSelector接口，而DeferredImportSelector是继承了ImportSelector：
public interface ImportSelector { String[] selectImports(AnnotationMetadata var1);}ImportSelector接口次要是为了导入@Configuration的配置项，而DeferredImportSelector是延期导入，当所有的@Configuration都解决过后才会执行。
咱们看看AutoConfigurationImportSelector实现的selectImports办法：
public String[] selectImports(AnnotationMetadata annotationMetadata) { // 判断是否进行主动拆卸 if (!this.isEnabled(annotationMetadata)) { return NO_IMPORTS; } else { //1加载META-INF/spring-autoconfigure-metadata.properties文件 AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader); AutoConfigurationImportSelector.AutoConfigurationEntry autoConfigurationEntry = this.getAutoConfigurationEntry(autoConfigurationMetadata, annotationMetadata); return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations()); } } protected AutoConfigurationImportSelector.AutoConfigurationEntry getAutoConfigurationEntry(AutoConfigurationMetadata autoConfigurationMetadata, AnnotationMetadata annotationMetadata) { if (!this.isEnabled(annotationMetadata)) { return EMPTY_ENTRY; } else { //2获取注解的属性及其值（PS：注解指的是@EnableAutoConfiguration注解） AnnotationAttributes attributes = this.getAttributes(annotationMetadata); //3.在classpath下所有的META-INF/spring.factories文件中查找org.springframework.boot.autoconfigure.EnableAutoConfiguration的值，并将其封装到一个List中返回 List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes); //4.对上一步返回的List中的元素去重、排序 configurations = this.removeDuplicates(configurations); //5.根据第2步中获取的属性值排除一些特定的类 Set<String> exclusions = this.getExclusions(annotationMetadata, attributes); //6.对上一步中所失去的List进行过滤，过滤的根据是条件匹配。这里用到的过滤器是 //org.springframework.boot.autoconfigure.condition.OnClassCondition最终返回的是一个ConditionOutcome[]数组。 //（PS：很多类都是依赖于其它的类的，当有某个类时才会拆卸，所以这次过滤的就是依据是否有某个 //class进而决定是否拆卸的。这些类所依赖的类都写在META-INF/spring-autoconfigure-metadata.properties文件里） this.checkExcludedClasses(configurations, exclusions); configurations.removeAll(exclusions); configurations = this.filter(configurations, autoConfigurationMetadata); this.fireAutoConfigurationImportEvents(configurations, exclusions); return new AutoConfigurationImportSelector.AutoConfigurationEntry(configurations, exclusions); } } .... public static AutoConfigurationMetadata loadMetadata(ClassLoader classLoader) { return loadMetadata(classLoader, "META-INF/spring-autoconfigure-metadata.properties"); }}从下面的源码得悉，该办法先判断是否进行主动拆卸，而后从META-INF/spring-autoconfigure-metadata.properties读取元数据与元数据的相干属性，而后调用getCandidateConfigurations办法：
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) { List<String> configurations = SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.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;}这个时候咱们看到个Spring框架原有的一个工具类SpringFactoriesLoader，其次要的工作是从指定的META-INF/spring.factories加载配置，即依据@EnableAutoConfiguration的残缺类名"org.springframework.boot.autoconfigure.EnableAutoConfiguration"作为查找的Key，获取对应的配置，通过反射失去对应的一组@Configuration类。spring.factories中EnableAutoConfiguration如下：
# Auto Configureorg.springframework.boot.autoconfigure.EnableAutoConfiguration=\org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\org.springframework.boot.autoconfigure.cloud.CloudServiceConnectorsAutoConfiguration,\org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\....总结：主动拆卸就是利用SpringFactoriesLoader从classpath中搜寻所有的META-INF/spring.factories配置文件，并将其中org.springframework.boot.autoconfigure.EnableAutoConfiguration对应的配置项通过反射实例化为标注了@Configuration的JavaConfig模式的配置类，而后汇总并加载到ioc容器。所以，以前咱们须要本人配置的货色，主动配置类都帮咱们实现了，是不是很嗨～～～