2.1 父依赖: starter-parent

helloworld查看依赖: 我的项目依赖了 spring-boot-stater-parent:

<dependency>    <groupId>org.springframework.boot</groupId>    <artifactId>spring-boot-starter-parent</artifactId></dependency>

spring-boot-stater-parent点进去, 外面还依赖了个parent:

<parent>  <groupId>org.springframework.boot</groupId>  <artifactId>spring-boot-dependencies</artifactId>  <version>2.3.2.RELEASE</version></parent>

spring-boot-dependencies再点进去:

一大堆 properties

一大堆 dependencies

可见:

spring-boot-dependencies 才是springboot 所有依赖真正管理者;

2.2 导入的依赖: starter-web

<dependency>    <groupId>org.springframework.boot</groupId>    <artifactId>spring-boot-starter-web</artifactId> </dependency>

点进去: spring-boot-starter-web帮咱们导入了web我的项目所依赖的依赖项:

<dependencies>  <dependency>    <groupId>org.springframework.boot</groupId>    <artifactId>spring-boot-starter</artifactId>    <version>2.3.2.RELEASE</version>    <scope>compile</scope>  </dependency>  <dependency>    <groupId>org.springframework.boot</groupId>    <artifactId>spring-boot-starter-json</artifactId>    <version>2.3.2.RELEASE</version>    <scope>compile</scope>  </dependency>  <dependency>    <groupId>org.springframework.boot</groupId>    <artifactId>spring-boot-starter-tomcat</artifactId>    <version>2.3.2.RELEASE</version>    <scope>compile</scope>  </dependency>  <dependency>    <groupId>org.springframework</groupId>    <artifactId>spring-web</artifactId>    <version>5.2.8.RELEASE</version>    <scope>compile</scope>  </dependency>  <dependency>    <groupId>org.springframework</groupId>    <artifactId>spring-webmvc</artifactId>    <version>5.2.8.RELEASE</version>    <scope>compile</scope>  </dependency></dependencies>
  1. spring-boot-starter
  2. spring-boot-starter-json
  3. spring-boot-starter-tomcat
  4. spring-web
  5. spring-webmvc

starter: spring boot帮忙治理依赖资源;

spring提供了一系列starter: mail/web/jpa/mq...

2.3 @SpringBootApplication注解

注解类:

//....SpringBootApplication...@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@SpringBootConfiguration // 1@EnableAutoConfiguration // 2@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),      @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })public @interface SpringBootApplication {.....    //....SpringBootConfiguration...@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Configuration    // 3public @interface SpringBootConfiguration {    .....    //....Configuration...@Target({ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documented@Component // 4public @interface Configuration {

次要注解类:

2.4 SpringBootApplication之@SpringBootConfiguration

SpringBootConfiguration能够看到, 有 Configuration所以:

2.4.1 申明Application类为一个配置类

SpringBootApplication -> SpringBootConfiguration -> Configuration -> Component

注解了 @SpringBootApplication 就有了 @SpringBootConfiguration;

就有了 @Configuration 的性能; 即:此类是配置类!

就有了 @Component 的性能;

@Target({ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documented@Configuration // 继承了Componentpublic @interface SpringBootConfiguration {

下面阐明: HelloApplication.java注解了@SpringBootApplication 它就是一个配置类, 能够被 AnnotationConfigApplicationContext加载扫描起来!

2.5 SpringBootApplication之@EnableAutoConfiguration

按需主动注入spring.factories组件

2.5.1 EnableAutoConfiguration注解原理

  1. 门路: org.springframework.boot.autoconfigure.EnableAutoConfiguration

  2. 此类所属jar包 spring-boot-autoconfigure.jar 目录下有 META-INF/spring.factories文件, 内容如下: 能够这么了解: 上面所有类都是配置类, 作用都相似于写一个 @Configuration的类, 在其中初始化相应所须要的的 @Bean;

    # Initializersorg.springframework.context.ApplicationContextInitializer=\org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener# Application Listenersorg.springframework.context.ApplicationListener=\org.springframework.boot.autoconfigure.BackgroundPreinitializer# Auto Configuration Import Listenersorg.springframework.boot.autoconfigure.AutoConfigurationImportListener=\org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener# Auto Configuration Import Filtersorg.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\org.springframework.boot.autoconfigure.condition.OnBeanCondition,\org.springframework.boot.autoconfigure.condition.OnClassCondition,\org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition# Auto Configureorg.springframework.boot.autoconfigure.EnableAutoConfiguration=\org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\............省略100多个....# Failure analyzersorg.springframework.boot.diagnostics.FailureAnalyzer=\org.springframework.boot.autoconfigure.data.redis.RedisUrlSyntaxFailureAnalyzer,\org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\org.springframework.boot.autoconfigure.flyway.FlywayMigrationScriptMissingFailureAnalyzer,\org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer,\org.springframework.boot.autoconfigure.r2dbc.ConnectionFactoryBeanCreationFailureAnalyzer,\org.springframework.boot.autoconfigure.session.NonUniqueSessionRepositoryFailureAnalyzer# Template availability providersorg.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\org.springframework.boot.autoconfigure.mustache.MustacheTemplateAvailabilityProvider,\org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAvailabilityProvider,\org.springframework.boot.autoconfigure.thymeleaf.ThymeleafTemplateAvailabilityProvider,\org.springframework.boot.autoconfigure.web.servlet.JspTemplateAvailabilityProvider

2.5.2 EnableAutoConfiguration的继承关系

//....EnableAutoConfiguration...@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@AutoConfigurationPackage // 5@Import(AutoConfigurationImportSelector.class) // 6public @interface EnableAutoConfiguration {}//....AutoConfigurationPackage...@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@Import(AutoConfigurationPackages.Registrar.class)     // 7public @interface AutoConfigurationPackage {}// ...Registrar...// ...ImportBeanDefinitionRegistrar.../** * {@link ImportBeanDefinitionRegistrar} to store the base package from the importing * configuration. */static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {    @Override    public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {        register(registry, new PackageImports(metadata).getPackageNames().toArray(new String[0]));    }    @Override    public Set<Object> determineImports(AnnotationMetadata metadata) {        return Collections.singleton(new PackageImports(metadata));    }}// ImportBeanDefinitionRegistrar 能够在spring容器bean初始化的时候注入组件到容器中

// 6 处是一个 ImportSelector

// 7 处是一个ImportBeanDefinitionRegistrar

这两处都是往容器中注册bean, 具体参见笔记:

spring注解驱动开发-(5) 向Spring容器中注册组件的办法

ImportBeanDefinitionRegistrar 能够在spring容器bean初始化的时候注入组件到容器中: 在这里打断点能够看到: 会把 com.niewj.springboot 包目录注册进去; 这样, 此包下所有子包中的spring注解的类就都会被扫描, 并初始化注册到spring容器的上下文;

这样的话, spring容器在启动容器的时候, 就会按需加载 spring-boot-autoconfigure.jar包下的META-INF/spring.factories中配置的加载类; 达到主动配置注入bean到容器中的成果(目标就是不便开发, 不须要可怜的程序员一个一个写@Configuration的类, 而后本人写@Bean的办法注册组件) 这种机制就是 SPI 深刻了解SPI机制