@SpringBootApplication注解的理解

@SpringBootApplication

废话不多说，我们直接贴出来SpringBoot的官方给出的源码:

package org.springframework.boot.autoconfigure;

@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 {

}

可以分为这两类:
第一类
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited

第二类
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan


第一类我们忽略，直接看第二类
下面是每一类的源码：

@SpringBootConfiguration

package org.springframework.boot;

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

}

@EnableAutoConfiguration

package org.springframework.boot.autoconfigure;

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {

}

@ComponentScan

package org.springframework.context.annotation;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Repeatable(ComponentScans.class)
public @interface ComponentScan {
}

于此得出@SpringBootApplication由@SpringBootConfiguration@EnableAutoConfiguration@ComponentScan组成。

我们来看看官方https://docs.spring.io/spring-boot/docs/2.2.6.RELEASE/api/ API是怎么解释的

@SpringBootApplication 注解在这个包目录下 org.springframework.boot.autoconfigure;

重点就是这句话“Indicates a configuration class that declares one or more @Bean methods and also triggers auto-configuration and component scanning. This is a convenience annotation that is equivalent to declaring @Configuration, @EnableAutoConfiguration and @ComponentScan.”

我们翻一下：

指示一个配置类，该类声明一个或多个@Bean方法，并且还触发自动配置和组件扫描。这是一个方便注释，等效于声明@ Configuration，@ EnableAutoConfiguration和@ComponentScan。

从中我们可以明确的知道@SpringBootApplication==@Configuration+@EnableAutoConfiguration+@ComponentScan