SpringBoot运行原理


"1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0modelVersion>
  <groupId>org.springframework.bootgroupId>
  <artifactId>spring-boot-dependenciesartifactId>
  <version>2.7.3version>
  <packaging>pompackaging>
  <name>spring-boot-dependenciesname>
  <description>Spring Boot Dependenciesdescription>
  <url>https://spring.io/projects/spring-booturl>
  <licenses>
    <license>
      <name>Apache License, Version 2.0name>
      <url>https://www.apache.org/licenses/LICENSE-2.0url>
    license>
  licenses>
  <developers>
    <developer>
      <name>Pivotalname>
      <email>info@pivotal.ioemail>
      <organization>Pivotal Software, Inc.organization>
      <organizationUrl>https://www.spring.ioorganizationUrl>
    developer>
  developers>
  <scm>
    <url>https://github.com/spring-projects/spring-booturl>
  scm>

因此，我们在写或者引入一些SpringBoot依赖的时候，不需要指定版本（因为有这些版本仓库）

二、启动器（spring-boot-starter）


 
<dependency>
    <groupId>org.springframework.bootgroupId>
    <artifactId>spring-boot-starter-webartifactId>
dependency>


<dependencies>
    <dependency>
        <groupId>org.springframework.bootgroupId>
        <artifactId>spring-boot-starter-webartifactId>
    dependency>
    <dependency>
        <groupId>org.springframework.bootgroupId>
        <artifactId>spring-boot-starter-testartifactId>
        <scope>testscope>
    dependency>
dependencies>

spring-boot-starter-web：帮助自动导入web环境所有的依赖
SpringBoot将所有的功能场景都抽取出来，做成一个个的starter （启动器），只需要在项目中引入这些starter即可，所有相关的依赖都会导入进来
也可以自己自定义 starter；

三、主启动类


//标注该类是一个SpringBoot的应用：启动类下的所有资源被导入
@SpringBootApplication
public class HelloworldApplication {
 
    public static void main(String[] args) {
        //将SpringBoot应用启动
        SpringApplication.run(HelloworldApplication.class, args);
    }
}

@SpringBootApplication源码


//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//
 
 
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
//@ComponentScan：自动扫描并加载符合条件的组件或者bean ， 将这个bean定义加载到IOC容器中
@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"
    )
    Classextends BeanNameGenerator> nameGenerator() default BeanNameGenerator.class;
 
    @AliasFor(
        annotation = Configuration.class
    )
    boolean proxyBeanMethods() default true;
}

@SpringBootConfiguration（源码）

springboot的配置


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


@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component  //说明这也是一个spring组件
public @interface Configuration {
    @AliasFor(
        annotation = Component.class
    )
    String value() default "";
 
    boolean proxyBeanMethods() default true;
}

@EnableAutoConfiguration源码

@EnableAutoConfiguration：自动配置，告诉SpringBoot开启自动配置功能，这样自动配置才能生效；


@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage  //自动配置包
@Import({AutoConfigurationImportSelector.class}) //自动配置导入选择
public @interface EnableAutoConfiguration {
    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
 
    Class[] exclude() default {};
 
    String[] excludeName() default {};
}


@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import({Registrar.class})  //自动配置包注册
public @interface AutoConfigurationPackage {
    String[] basePackages() default {};
 
    Class[] basePackageClasses() default {};
}


static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {
    Registrar() {
    }
    public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
        AutoConfigurationPackages.register(registry, (String[])(new AutoConfigurationPackages.PackageImports(metadata)).getPackageNames().toArray(new String[0]));
    }
    public Set