核心注解

1.@SpringBootApplication 注解是Springboot的核心注解, 也是一个组合注解

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(
    excludeFilters = {@Filter(
    type = FilterType.CUSTOM,
    classes = {TypeExcludeFilter.class}
), @Filter(
    type = FilterType.CUSTOM,
    classes = {AutoConfigurationExcludeFilter.class}
)}
)
public @interface SpringBootApplication {
    省略 .....
}

2.@SpringBootConfiguration

配置注解, 也是一个组合注解, Springboot项目中推荐使用@SpringBootConfiguration代替@Configuration

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {
}

3.@EnableAutoConfiguration

启动自动配置，该注解会使Springboot根据项目中依赖的jar包自动配置项目的配置项

例如：我们添加了spring-boot-starter-web的依赖， 项目中也就会引入SpringMVC的依赖，Springboot就会自动配置tomcat和SpringMVC

4.@ComponentScan

默认扫描@SpringBootApplication所在类的同级目录及它的子目录