Spring Boot 自动配置特性

https://www.bilibili.com/video/BV19K4y1L7MT/?p=7

怎么自动配好 Tomcat的？

怎么引入 tomcat 依赖的？

boot-01-helloworld - pom.xml

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

    </dependencies>

spring-boot-starter-web-x.x.x.RELEASE.pom

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-tomcat</artifactId>
      <version>2.3.4.RELEASE</version>
      <scope>compile</scope>
    </dependency>

自动配置好 Spring MVC

spring-boot-starter-web-x.x.x.RELEASE.pom

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <version>5.2.9.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-webmvc</artifactId>
      <version>5.2.9.RELEASE</version>
      <scope>compile</scope>
    </dependency>

思考：在 Spring Boot 出现之前，使用 Spring MVC 要有哪些配置？

web.xml

<!--配置DispatcherServlet -->
  <servlet>
    <servlet-name>spring-dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <!-- 配置SpringMVC需要加载的配置文件 spring-mvc.xml -->
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath:spring-mvc.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>spring-dispatcher</servlet-name>
    <!--默认匹配所有的请求 -->
    <url-pattern>/</url-pattern>
  </servlet-mapping>

为什么在 Spring Boot 出现之后，不进行如上的配置也可以进行使用；如果这些配置已经在 Spring Boot 内部实现了，是怎么实现的？

打印容器中所有的 bean

package io.github.jihch.boot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;


/**
 * 主程序类
 * @SpringBootApplication：这是一个 Spring Boot 应用
 */
@SpringBootApplication
public class MainApplication {

    public static void main(String[] args) {
        //1、返回 IOC 容器
        ConfigurableApplicationContext context = SpringApplication.run(MainApplication.class, args);

        //2、查看容器里面的组件
        String[] beanDefinitionNames = context.getBeanDefinitionNames();
        Arrays.sort(beanDefinitionNames);
        for (String name : beanDefinitionNames) {
            System.out.println(name);
        }
    }

}

applicationAvailability
applicationTaskExecutor
basicErrorController
beanNameHandlerMapping
beanNameViewResolver
characterEncodingFilter
conventionErrorViewResolver
defaultServletHandlerMapping
defaultViewResolver
dispatcherServlet
dispatcherServletRegistration
error
errorAttributes
errorPageCustomizer
errorPageRegistrarBeanPostProcessor
formContentFilter
handlerExceptionResolver
handlerFunctionAdapter
helloController
httpRequestHandlerAdapter
jacksonObjectMapper
jacksonObjectMapperBuilder
jsonComponentModule
lifecycleProcessor
localeCharsetMappingsCustomizer
mainApplication
mappingJackson2HttpMessageConverter
messageConverters
multipartConfigElement
multipartResolver
mvcContentNegotiationManager
mvcConversionService
mvcHandlerMappingIntrospector
mvcPathMatcher
mvcResourceUrlProvider
mvcUriComponentsContributor
mvcUrlPathHelper
mvcValidator
mvcViewResolver
org.springframework.aop.config.internalAutoProxyCreator
org.springframework.boot.autoconfigure.AutoConfigurationPackages
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration$ClassProxyingConfiguration
org.springframework.boot.autoconfigure.availability.ApplicationAvailabilityAutoConfiguration
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration
org.springframework.boot.autoconfigure.context.LifecycleAutoConfiguration
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration$StringHttpMessageConverterConfiguration
org.springframework.boot.autoconfigure.http.JacksonHttpMessageConvertersConfiguration
org.springframework.boot.autoconfigure.http.JacksonHttpMessageConvertersConfiguration$MappingJackson2HttpMessageConverterConfiguration
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration
org.springframework.boot.autoconfigure.internalCachingMetadataReaderFactory
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration$Jackson2ObjectMapperBuilderCustomizerConfiguration
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration$JacksonObjectMapperBuilderConfiguration
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration$JacksonObjectMapperConfiguration
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration$ParameterNamesModuleConfiguration
org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration
org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration$TomcatWebServerFactoryCustomizerConfiguration
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration$DispatcherServletConfiguration
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration$DispatcherServletRegistrationConfiguration
org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryConfiguration$EmbeddedTomcat
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration$EnableWebMvcConfiguration
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration$WebMvcAutoConfigurationAdapter
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration$DefaultErrorViewResolverConfiguration
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration$WhitelabelErrorViewConfiguration
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration$TomcatWebSocketConfiguration
org.springframework.boot.context.internalConfigurationPropertiesBinder
org.springframework.boot.context.internalConfigurationPropertiesBinderFactory
org.springframework.boot.context.properties.BoundConfigurationProperties
org.springframework.boot.context.properties.ConfigurationBeanFactoryMetadata
org.springframework.boot.context.properties.ConfigurationPropertiesBindingPostProcessor
org.springframework.context.annotation.internalAutowiredAnnotationProcessor
org.springframework.context.annotation.internalCommonAnnotationProcessor
org.springframework.context.annotation.internalConfigurationAnnotationProcessor
org.springframework.context.event.internalEventListenerFactory
org.springframework.context.event.internalEventListenerProcessor
parameterNamesModule
preserveErrorControllerTargetClassPostProcessor
propertySourcesPlaceholderConfigurer
requestContextFilter
requestMappingHandlerAdapter
requestMappingHandlerMapping
resourceHandlerMapping
restTemplateBuilder
routerFunctionMapping
server-org.springframework.boot.autoconfigure.web.ServerProperties
servletWebServerFactoryCustomizer
simpleControllerHandlerAdapter
spring.info-org.springframework.boot.autoconfigure.info.ProjectInfoProperties
spring.jackson-org.springframework.boot.autoconfigure.jackson.JacksonProperties
spring.lifecycle-org.springframework.boot.autoconfigure.context.LifecycleProperties
spring.mvc-org.springframework.boot.autoconfigure.web.servlet.WebMvcProperties
spring.resources-org.springframework.boot.autoconfigure.web.ResourceProperties
spring.servlet.multipart-org.springframework.boot.autoconfigure.web.servlet.MultipartProperties
spring.task.execution-org.springframework.boot.autoconfigure.task.TaskExecutionProperties
spring.task.scheduling-org.springframework.boot.autoconfigure.task.TaskSchedulingProperties
standardJacksonObjectMapperBuilderCustomizer
stringHttpMessageConverter
taskExecutorBuilder
taskSchedulerBuilder
tomcatServletWebServerFactory
tomcatServletWebServerFactoryCustomizer
tomcatWebServerFactoryCustomizer
viewControllerHandlerMapping
viewResolver
webServerFactoryCustomizerBeanPostProcessor
websocketServletWebServerCustomizer
welcomePageHandlerMapping

我们可以发现，已经有了 dispatcherServlet 和 characterEncodingFilter