Configuration配置和ConfigurationProperties加载外部配置注解的使用

那么在Spring boot项目中，应用上下文又是如何找到那么多配置并加载初始化好的呢？

@SpringBootApplication
spring boot项目推荐大家在主类中标注@SpringBootApplication这个注解，我们来看看它的源码：
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration //配置
@EnableAutoConfiguration //启用自动配置
//组件扫描
@ComponentScan(excludeFilters = @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class))
public @interface SpringBootApplication {
//需要排除的自动配置类
Class<?>[] exclude() default {};
//需要排除的自动配置类类名
String[] excludeName() default {};

 //扫描包路径

@AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
String[] scanBasePackages() default {};

  //扫描包路径类

@AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
Class<?>[] scanBasePackageClasses() default {};
}
@EnableAutoConfiguration
我们发现一个配置开关注解，名字叫@EnableAutoConfiguration，看看它的源码：
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(EnableAutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {

//是否启用自动配置的总开关名

String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
//需要排除的自动配置类
Class<?>[] exclude() default {};

//需要排除的自动配置类类名

String[] excludeName() default {};
}
EnableAutoConfigurationImportSelector
我们看到有一个@Import导入了选择器EnableAutoConfigurationImportSelector.class，看看它的源码：
public class EnableAutoConfigurationImportSelector

  implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware,  BeanFactoryAware, EnvironmentAware, Ordered {

...