SpringBoot开发笔记-(2) springboot原理初探-解析helloworld

上一节:SpringBoot开发笔记-(1) springboot简介和helloworld

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2.1 父依赖: starter-parent

helloworld查看依赖: 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, 里面还依赖了个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 全部依赖真正管理者;

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帮助管理依赖资源;

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    // 3
public @interface SpringBootConfiguration {
    
.....
    
//....Configuration...
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component // 4
public @interface Configuration {

主要注解类:

2.4 SpringBootApplication之@SpringBootConfiguration

SpringBootConfiguration能够看到, 有 Configuration因此:

2.4.1 声明Application类为一个配置类

SpringBootApplication -> SpringBootConfiguration -> Configuration -> Component

注解了 @SpringBootApplication 就有了 @SpringBootConfiguration;

就有了 @Configuration 的功能; 即:此类是配置类!

就有了 @Component 的功能;

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

上面说明: 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

按需自动注入spring.factories组件

2.5.1 EnableAutoConfiguration注解原理

1. 路径: 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, 内容以下: 能够这么理解: 下面全部类都是配置类, 做用都相似于写一个 @Configuration的类, 在其中初始化相应所须要的的 @Bean;

   # Initializers
   org.springframework.context.ApplicationContextInitializer=\
   org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
   org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
   
   # Application Listeners
   org.springframework.context.ApplicationListener=\
   org.springframework.boot.autoconfigure.BackgroundPreinitializer
   
   # Auto Configuration Import Listeners
   org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\
   org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener
   
   # Auto Configuration Import Filters
   org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
   org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
   org.springframework.boot.autoconfigure.condition.OnClassCondition,\
   org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition
   
   # Auto Configure
   org.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 analyzers
   org.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 providers
   org.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) // 6
public @interface EnableAutoConfiguration {}

//....AutoConfigurationPackage...
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(AutoConfigurationPackages.Registrar.class)     // 7
public @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容器中注册组件的方法

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, 此包下全部子包中的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; 达到自动配置注入bean到容器中的效果(目的就是方便开发, 不须要可怜的程序员一个一个写@Configuration的类, 而后本身写@Bean的方法注册组件) 这种机制就是 SPI 深刻理解SPI机制