③. @ComponentScan
- 扫描标明了@SpringBootApplication的类或及其子包进行一个扫描
@Retention(RetentionPolicy.RUNTIME) @Target({ElementType.TYPE}) @Documented @Repeatable(ComponentScans.class) public @interface ComponentScan {
④. @EnableAutoConfiguration
- ①. 主要的代码如下
@Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @AutoConfigurationPackage @Import({AutoConfigurationImportSelector.class}) public @interface EnableAutoConfiguration {
②. @AutoConfigurationPackage:给容器中导入一个组件,利用Registrar给容器导入一系列组件,将指定的一个包下的所有组件导入进来(MainApplication所在的包下)
③. @Import(AutoConfigurationImportSelector.class)
(1). 利用getAutoConfigurationEntry(annotationMetadata);给容器中批量导入一些组件
(2). 调用List configurations = getCandidateConfigurations(annotationMetadata, attributes)获取到所有需要导入到容器中的配置类
(3). 利用工厂加载 Map<String, List> loadSpringFactories(@Nullable ClassLoader classLoader):得到所有的组件
(4). 从META-INF/spring.factories位置来加载一个文件。
默认扫描我们当前系统里面所有META-INF/spring.factories位置的文件
spring-boot-autoconfigure-2.3.4.RELEASE.jar包里面也有META-INF/spring.factories
并不是所有的Bean都会被初始化,在配置类中使用Condition来加载满足条件的Bean
public String[] selectImports(AnnotationMetadata annotationMetadata) { if (!this.isEnabled(annotationMetadata)) { return NO_IMPORTS; } else { //(1). 利用getAutoConfigurationEntry(annotationMetadata);给容器中批量导入一些组件 AutoConfigurationImportSelector.AutoConfigurationEntry autoConfigurationEntry = this.getAutoConfigurationEntry(annotationMetadata); return StringUtils.toStringArray(autoConfigurationEntry.getConfigurations()); } } protected AutoConfigurationImportSelector.AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) { if (!this.isEnabled(annotationMetadata)) { return EMPTY_ENTRY; } else { AnnotationAttributes attributes = this.getAttributes(annotationMetadata); //(2). 调用List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes) //获取到所有需要导入到容器中的配置类 List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes); configurations = this.removeDuplicates(configurations); Set<String> exclusions = this.getExclusions(annotationMetadata, attributes); this.checkExcludedClasses(configurations, exclusions); configurations.removeAll(exclusions); configurations = this.getConfigurationClassFilter().filter(configurations); this.fireAutoConfigurationImportEvents(configurations, exclusions); return new AutoConfigurationImportSelector.AutoConfigurationEntry(configurations, exclusions); } } 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; } //(3). 利用工厂加载 Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader //classLoader)得到所有的组件 public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) { String factoryTypeName = factoryType.getName(); return (List)loadSpringFactories(classLoader).getOrDefault(factoryTypeName, 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 { //(4). 从META-INF/spring.factories位置来加载一个文件 Enumeration<URL> urls = classLoader != null ? classLoader.getResources ("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories"); LinkedMultiValueMap result = new LinkedMultiValueMap();
