查看“Spring Boot 自动配置特性”的源代码

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<syntaxhighlight lang="xml">
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

    </dependencies>
</syntaxhighlight>


spring-boot-starter-web-x.x.x.RELEASE.pom<syntaxhighlight lang="xml">
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-tomcat</artifactId>
      <version>2.3.4.RELEASE</version>
      <scope>compile</scope>
    </dependency>
</syntaxhighlight>



=== 自动配置好 Spring MVC ===
spring-boot-starter-web-x.x.x.RELEASE.pom<syntaxhighlight lang="xml">
    <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>
</syntaxhighlight>



=== 思考：在 Spring Boot 出现之前，使用 Spring MVC 要有哪些配置？ ===
web.xml<syntaxhighlight lang="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>
</syntaxhighlight>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 ====
<syntaxhighlight lang="java">
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);
        }
    }

}
</syntaxhighlight><syntaxhighlight lang="console">
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
</syntaxhighlight>我们可以发现，已经有了：

* dispatcherServlet 前端转发控制器 
* characterEncodingFilter 字符集编码过滤器
* 各种解析器
**viewResolver 视图解析器
**beanNameViewResolver 
**defaultViewResolver 
**conventionErrorViewResolver
**mvcViewResolver
**multipartResolver 文件上传解析器
* helloController 用 @RestController 注解的类的实例 bean



=== 默认的包扫描规则/如何组织包结构 ===
https://docs.spring.io/spring-boot/docs/2.4.13/reference/html/using-spring-boot.html#using-boot-structuring-your-code

==== 默认的包结构 ====

* 主程序所在包及其下面的所有子包里面的所有组件都会被默认扫描并初始化为容器中的 bean。所以 io.github.jihch.boot.MainApplication 运行之后可以直接找到 @RestController 注解的类  io.github.jihch.boot.controller.HelloController 的实例 bean。但如果类被定义在了上层包中，比如：<syntaxhighlight lang="java">
package io.github.jihch;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class WorldController {

    @RequestMapping("/w")
    public String world66() {
        return "World";
    }

}
</syntaxhighlight>容器中就找不到对应的 bean，URL 访问也是 404。如果就是要放在上层路径中，那么可以通过<syntaxhighlight lang="java">
@SpringBootApplication(scanBasePackages = "io.github.jihch")
</syntaxhighlight>中的 <code>scanBasePackages</code> 来指定要扫描的包。
:还可以在同级或子级包的配置类（使用了 <code>@Configuration</code> 注解的类）中，使用 <code>@ComponentScan("io.github.jihch")</code> 来指定要扫描的包



===各种自动配置都拥有默认值===
https://docs.spring.io/spring-boot/docs/2.7.8/reference/html/application-properties.html#appendix.application-properties

这些默认配置的值最终都是绑定到 Java 类的，这些类会在容器中创建对象

pom.xml 中增加：<syntaxhighlight lang="xml">
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
</syntaxhighlight>
依赖，可以实现点击配置文件的属性跳转到对应的配置类






===引入了哪些场景 starter，那些 starter 的自动配置才会开启 ===
所有的 starter 都会依赖 spring-boot-starter，spring-boot-starter 又依赖了 spring-boot-autoconfigure，yml 中的所有自动配置项对应绑定到的 XXXProperties 类都在 spring-boot-autoconfigure 这个包里面，

而这个包里面的 XXXAutoConfiguration 都使用了 <code>@ConditionalOnClass</code> 进行条件判断，因为各种各样的 starter 会把类加载到类路径中，容器启动时扫描类路径就知道哪些 <code>@ConditionalOnClass</code> 是成立的，

然后就会再实例化对应的配置属性类 XXXProperties、绑定 yml 中的参数到这个类的对象，如果没有对应参数就会使用默认参数配置。


Spring Boot 所有的自动配置功能都在<syntaxhighlight lang="xml">
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-autoconfigure</artifactId>
</syntaxhighlight>spring-boot-autoconfigure-x.x.x.RELEASE.jar 里