@SpringBootApplication注解

 启动类的

@SpringBootApplication

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//package org.springframework.boot.autoconfigure;import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.beans.factory.support.BeanNameGenerator;
import org.springframework.boot.SpringBootConfiguration;
import org.springframework.boot.context.TypeExcludeFilter;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.context.annotation.ComponentScan.Filter;
import org.springframework.core.annotation.AliasFor;@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 {@AliasFor(annotation = EnableAutoConfiguration.class)Class<?>[] exclude() default {};@AliasFor(annotation = EnableAutoConfiguration.class)String[] excludeName() default {};@AliasFor(annotation = ComponentScan.class,attribute = "basePackages")String[] scanBasePackages() default {};@AliasFor(annotation = ComponentScan.class,attribute = "basePackageClasses")Class<?>[] scanBasePackageClasses() default {};@AliasFor(annotation = ComponentScan.class,attribute = "nameGenerator")Class<? extends BeanNameGenerator> nameGenerator() default BeanNameGenerator.class;@AliasFor(annotation = Configuration.class)boolean proxyBeanMethods() default true;
}

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

@SpringBootConfiguration 之上有 @Configuration

所以加上@SpringBootApplication之后，会被当做配置类

--------------------------------------------------------------------------------

@Configuration

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//package org.springframework.context.annotation;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.core.annotation.AliasFor;
import org.springframework.stereotype.Component;@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {@AliasFor(annotation = Component.class)String value() default "";boolean proxyBeanMethods() default true;
}

其上有@Component 注解，所以 有@Configuration注解的类会创建bean对象交由spring容器去管理

@AliasFor(annotation = Component.class
)
String value() default "";

@Configuration注解 的value属性之上有注解@AliasFor( annotation = Component.class )

在使用@Configuration(value="s"),该属性的值将传给@Component的value属性，相当于有了@Component(value='s')的效果

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@SpringBootApplication 之上的@EnableAutoConfiguration

开启自动配置

@SpringBootApplication 之上的 @ComponentScan 开启组件扫描

Spring 自动扫描指定的基础包以及其子包中的所有类，并将被带有特定注解标记的类自动注册到 Spring 上下文中成为一个 Bean（basePackages 未指定，默认扫描当前包及子包）

在@SpringBootApplication 中  其属性scanBasePackages 为@ComponentScan注解的 basePackages属性的别名，@SpringBootApplication(scanBasePackages=S) 就有@ComponentScan(basePackages=S)的效果

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