SpringBoot核心注解@SpringBootApplication和自动配置原理

@SpringBootApplication注解

@SpringBootApplication是一个3合一注解：

//@SpringBootApplication
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan
public @interface SpringBootApplication {
   
   
    
}

@SpringBootConfiguration

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.springframework.boot;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.annotation.AliasFor;

@Target({
   
   ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {
   
   
    @AliasFor(
        annotation = Configuration.class
    )
    boolean proxyBeanMethods() default true;
}

@Configuration，代表当前是一个配置类

@ComponentScan

指定扫描哪些包，Spring注解。

@EnableAutoConfiguration

@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
   
   

@AutoConfigurationPackage 导入主程序类所在的包及其子包

翻译过来叫自动配置包？指定了默认的包规则，看源码

@Import(AutoConfigurationPackages.Registrar.class)
public @interface AutoConfigurationPackage {
   
   

它导入了一个Registrar，这是个内部类，点进去看源码，debug调试

利用Registrar给容器中导入一系列组件，将指定的一个包com.atguigu.boot下的