1、SpringMVC自动配置概览

Spring Boot provides auto-configuration for Spring MVC that works well with most applications.(大多场景我们都无需自定义配置) The auto-configuration adds the following features on top of Spring’s defaults:

  • Inclusion of ContentNegotiatingViewResolver and BeanNameViewResolver beans.
    • 内容协商视图解析器和BeanName视图解析器
  • Support for serving static resources, including support for WebJars (covered later in this document)).
    • 静态资源（包括webjars）
  • Automatic registration of Converter, GenericConverter, and Formatter beans.
    • 自动注册 Converter，GenericConverter，Formatter
  • Support for HttpMessageConverters (covered later in this document).
    • 支持 HttpMessageConverters （后来我们配合内容协商理解原理）
  • Automatic registration of MessageCodesResolver (covered later in this document).
    • 自动注册 MessageCodesResolver （国际化用）
  • Static index.html support.
    • 静态index.html 页支持
  • Custom Favicon support (covered later in this document).
    • 自定义 Favicon  
  • Automatic use of a ConfigurableWebBindingInitializer bean (covered later in this document).
    • 自动使用 ConfigurableWebBindingInitializer ，（DataBinder负责将请求数据绑定到JavaBean上）

If you want to keep those Spring Boot MVC customizations and make more MVC customizations (interceptors, formatters, view controllers, and other features), you can add your own @Configuration class of type WebMvcConfigurer but without @EnableWebMvc. 不用@EnableWebMvc注解。使用 **@Configuration** + **WebMvcConfigurer** 自定义规则

If you want to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter, or ExceptionHandlerExceptionResolver, and still keep the Spring Boot MVC customizations, you can declare a bean of type WebMvcRegistrations and use it to provide custom instances of those components. 声明 **WebMvcRegistrations** 改变默认底层组件

If you want to take complete control of Spring MVC, you can add your own @Configuration annotated with @EnableWebMvc, or alternatively add your own @Configuration-annotated DelegatingWebMvcConfiguration as described in the Javadoc of @EnableWebMvc. **使用 ****@EnableWebMvc+@Configuration+DelegatingWebMvcConfiguration 全面接管SpringMVC**

2、简单功能分析

2.1 静态资源访问

1、静态资源目录

只要静态资源放在类路径下：只要它被叫做called /static (or /public or /resources or /META-INF/resources 访问：当前项目根路径/+静态资源名

原理：静态映射/** 它将拦截所有的访问请求 请求进去，会先去找Controller，看看能不能被处理。如果不能被处理就会被传入进静态资源处理器。静态资源也找不到则将响应404界面

人为可以改变静态资源路径，如下

spring:
  mvc:
    static-path-pattern: /res/**  

  resources:
    static-locations: [classpath:/haha/]

static-path-patterm 是设置请求路径拦截/静态资源访问前缀，其是虚拟路径 static-locations是配置静态资源文件

2、静态资源访问前缀

默认无前缀 可以修改 当前项目 + static-path-pattern + 静态资源名 = 静态资源文件夹下找

3、webjar

这也是一种静态资源访问格式 自动映射/webjars/** 如访问地址：http://localhost:8080/webjars/jquery/3.5.1/jquery.js   后面地址要按照依赖里面的包路径

2.2 欢迎页支持

静态资源路径下 index.html 可以配置静态资源路径 但是不可以配置静态资源的访问前缀。否则导致index.html不能被访问

spring:
#  mvc:
#    static-path-pattern: /res/**   这个会导致welcome page功能失效

  resources:
    static-locations: [classpath:/haha/]

controller能处理/index

2.3自定义 Favicon

让 favicon.ico文件放在静态资源目录下即可

spring:
#  mvc:
#    static-path-pattern: /res/**   这个会导致 Favicon 功能失效

2.4 静态资源配置原理 SpringBoot启动默认加载配置xxxAutoConfiguration 类（自动配置类） 关于SpringMVC功能的自动配置类 WebAutoConfiguration生效

@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class,
        ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {}

期中容器配了什么 WebMvcAutoConfiguration 中有一个WebMvcAutoConfigurationAdapter的内部类 此内部类对SpringMvc进行了一定配置 此类中 配置文件的相关属性和两个类WebMvcProperties==spring.mvc ResourceProperties==spring.resources进行了绑定

2、资源处理的默认规则

@Override
		public void addResourceHandlers(ResourceHandlerRegistry registry) {
			if (!this.resourceProperties.isAddMappings()) {
				logger.debug("Default resource handling disabled");
				return;
			}
			Duration cachePeriod = this.resourceProperties.getCache().getPeriod();
			CacheControl cacheControl = this.resourceProperties.getCache().getCachecontrol().toHttpCacheControl();
			//webjars的规则
            if (!registry.hasMappingForPattern("/webjars/**")) {
				customizeResourceHandlerRegistration(registry.addResourceHandler("/webjars/**")
						.addResourceLocations("classpath:/META-INF/resources/webjars/")
						.setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
			}
            
            //
			String staticPathPattern = this.mvcProperties.getStaticPathPattern();
			if (!registry.hasMappingForPattern(staticPathPattern)) {
				customizeResourceHandlerRegistration(registry.addResourceHandler(staticPathPattern)
						.addResourceLocations(getResourceLocations(this.resourceProperties.getStaticLocations()))
						.setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
			}
		}

spring:
#  mvc:
#    static-path-pattern: /res/**

  resources:
    add-mappings: false   禁用所有静态资源规则

@ConfigurationProperties(prefix = "spring.resources", ignoreUnknownFields = false)
public class ResourceProperties {

	private static final String[] CLASSPATH_RESOURCE_LOCATIONS = { "classpath:/META-INF/resources/",
			"classpath:/resources/", "classpath:/static/", "classpath:/public/" };

	/**
	 * Locations of static resources. Defaults to classpath:[/META-INF/resources/,
	 * /resources/, /static/, /public/].
	 */
	private String[] staticLocations = CLASSPATH_RESOURCE_LOCATIONS;

静态资源可以分为两类，一类是如jqurey等其他包自带的webjars，其在底层进行了配置，如果访问了webjars，其将会找到类路径下的classpath:/META-INF/resources/webjars/"

另一类是自己放在项目中的静态资源，在自动配置类当中进行了绑定，这也是SpringBoot可以默认在static等文件夹下找到静态资源的原因

** private static final String[] CLASSPATH_RESOURCE_LOCATIONS = { "classpath:/META-INF/resources/",** **            "classpath:/resources/", "classpath:/static/", "classpath:/public/" };**

3、欢迎页的处理规则

	HandlerMapping：处理器映射。保存了每一个Handler能处理哪些请求。	

	@Bean
		public WelcomePageHandlerMapping welcomePageHandlerMapping(ApplicationContext applicationContext,
				FormattingConversionService mvcConversionService, ResourceUrlProvider mvcResourceUrlProvider) {
			WelcomePageHandlerMapping welcomePageHandlerMapping = new WelcomePageHandlerMapping(
					new TemplateAvailabilityProviders(applicationContext), applicationContext, getWelcomePage(),
					this.mvcProperties.getStaticPathPattern());
			welcomePageHandlerMapping.setInterceptors(getInterceptors(mvcConversionService, mvcResourceUrlProvider));
			welcomePageHandlerMapping.setCorsConfigurations(getCorsConfigurations());
			return welcomePageHandlerMapping;
		}

	WelcomePageHandlerMapping(TemplateAvailabilityProviders templateAvailabilityProviders,
			ApplicationContext applicationContext, Optional<Resource> welcomePage, String staticPathPattern) {
		if (welcomePage.isPresent() && "/**".equals(staticPathPattern)) {
            //要用欢迎页功能，必须是/**
			logger.info("Adding welcome page: " + welcomePage.get());
			setRootViewName("forward:index.html");
		}
		else if (welcomeTemplateExists(templateAvailabilityProviders, applicationContext)) {
            // 调用Controller  /index
			logger.info("Adding welcome page template: index");
			setRootViewName("index");
		}
	}