官方文档目录：

https://docs.spring.io/spring-boot/docs/2.1.0.RELEASE/reference/htmlsingle/#boot-features-spring-mvc

 1. Spring MVC auto-configuration

　　Spring Boot 自动配置好了SpringMVC,以下是SpringBoot对SpringMVC的默认配置:

（WebMvcAutoConfiguration）

　　- Inclusion of `ContentNegotiatingViewResolver` and `BeanNameViewResolver` beans.
　　- 自动配置了ViewResolver（视图解析器：根据方法的返回值得到视图对象（View），视图对象决定如何渲染（转发？重定向？））

• • public class WebMvcAutoConfiguration {
    @Bean
    
            @ConditionalOnMissingBean
    
            public InternalResourceViewResolver defaultViewResolver() {
    
                InternalResourceViewResolver resolver = new InternalResourceViewResolver();
    
                resolver.setPrefix(this.mvcProperties.getView().getPrefix());
    
                resolver.setSuffix(this.mvcProperties.getView().getSuffix());
    
                return resolver;
    
            }
    
            @Bean
    
            @ConditionalOnBean({View.class})
    
            @ConditionalOnMissingBean
    
            public BeanNameViewResolver beanNameViewResolver() {
    
                BeanNameViewResolver resolver = new BeanNameViewResolver();
    
                resolver.setOrder(2147483637);
    
                return resolver;
    
            }
    
            @Bean
    
            @ConditionalOnBean({ViewResolver.class})
    
            @ConditionalOnMissingBean(
    
                name = {"viewResolver"},
    
                value = {ContentNegotiatingViewResolver.class}
    
            )
    
            public ContentNegotiatingViewResolver viewResolver(BeanFactory beanFactory) {
    
                ContentNegotiatingViewResolver resolver = new ContentNegotiatingViewResolver();
    
                resolver.setContentNegotiationManager(
    　　(ContentNegotiationManager)beanFactory.getBean(ContentNegotiationManager.class));
    
                resolver.setOrder(-2147483648);
    
                return resolver;
    
            }
    
        ......
    
    }

　　　　- ContentNegotiatingViewResolver：只配置一个@RequestMapping， 匹配多个 url

• public class ContentNegotiatingViewResolver implements ViewResolver, Ordered, InitializingBean { 

      @Nullable
  
      privateList<ViewResolver> viewResolvers;   //视图解析器
  
      //初始化方法
  
      protected void initServletContext(ServletContext servletContext) {
  
          //从容器中根据ViewResolver类型获取所有的视图解析器Collection<ViewResolver> matchingBeans = BeanFactoryUtils
  
                  .beansOfTypeIncludingAncestors(this.obtainApplicationContext(), ViewResolver.class).values();
  
          ViewResolver viewResolver;
  
          if (this.viewResolvers == null) {
  
              this.viewResolvers = new ArrayList(matchingBeans.size());
  
              Iterator var3 = matchingBeans.iterator();
  
              //遍历所有的视图解析器
  
              while(var3.hasNext()) {
  
                  viewResolver = (ViewResolver)var3.next();
  
                  if (this != viewResolver) {
  
                      //将所有的视图解析器加入到本地变量
  
                      this.viewResolvers.add(viewResolver);
  
                  }
  
              }
  
          } else {
  
              for(int i = 0; i < this.viewResolvers.size(); ++i) {
  
                  viewResolver = (ViewResolver)this.viewResolvers.get(i);
  
                  if (!matchingBeans.contains(viewResolver)) {
  
                      String name = viewResolver.getClass().getName() + i;
  
                      this.obtainApplicationContext().getAutowireCapableBeanFactory().initializeBean(viewResolver, name);
  
                  }
  
              }
  
          }
  
          AnnotationAwareOrderComparator.sort(this.viewResolvers);
  
         this.cnmFactoryBean.setServletContext(servletContext);
  
      }
  
      @Nullable
  
      publicView resolveViewName(String viewName, Locale locale) throws Exception {
  
          RequestAttributes attrs = RequestContextHolder.getRequestAttributes();
  
          Assert.state(attrs instanceof ServletRequestAttributes, "No current ServletRequestAttributes");
  
          List<MediaType> requestedMediaTypes = this.getMediaTypes(((ServletRequestAttributes)attrs).getRequest());
  
          if (requestedMediaTypes != null) {//只配置一个@RequestMapping， 匹配多个 url，所以要获取多个
  
              List<View> candidateViews = this.getCandidateViews(viewName, locale, requestedMediaTypes);//获取所有候选的视图对象
  
              View bestView = this.getBestView(candidateViews, requestedMediaTypes, attrs);//获取最佳视图对象（根据参数或类型选取）
  
              if (bestView != null) {
  
                  return bestView;
  
              }
  
          }
  
  }

• 自定义ViewResolver加入到Spring容器

• //springBoot启动类注解，包含@Configuration
  
  @SpringBootApplication
  
  public class DemoApplication {
  
      public static void main(String[] args) {
  
          SpringApplication.run(DemoApplication.class, args);
  
      }
  
      //将自定义的ViewResolver加入到Spring容器中
  
      @Bean
  
      public ViewResolver myViewResolver() {
  
          return new MyViewResover();
  
      }
  
      //自定义ViewResover
  
      public static class MyViewResover implements  ViewResolver {
  
          @Nullable
  
          @Override
  
          public View resolveViewName(String s, Locale locale) throws Exception {
  
              return null;
  
          }
  
      }
  
  }

• 当SpringBoot项目启动，随便发一个请求，进到DispatcherServlet的DoDispatch()方法时，能够获取到所有的ViewResolver,包括自定义的，被包含在了ContentNegotiatingViewResolver里

　　- 总结：如何定制视图解析器ViewResolver?：

　　　　根据@WebMvcAutoConfiguration

　　　　　　　　——》 @Bean ContentNegotiatingViewResolver viewResolver()

　　　　　　　　　　　　——》initServletContext（）中根据类型加载容器中所有的ViewResolver

　　　　我们可以自己给容器中添加一个视图解析器，@Bean加入到容器中，SpringBoot便自动的将其组合进来；

　　关于视图解析器详情在SprintMVC知识点中学习

 这些前面章节已有学过

　　- Support for serving static resources, including support for WebJars (see below).静态资源文件夹路径,webjars

　　- Static `index.html` support. 静态首页访问

　　- Custom `Favicon` support (see below). favicon.ico

- 自动注册了 of `Converter`, `GenericConverter`, `Formatter` beans.

　　- Converter：转换器； public String hello(User user)：类型转换使用Converter      （如果页面传参和User对象类型一一对应，不用转换，如果对应不上就需要转换）
　　- `Formatter` 格式化器； 2017.12.17   /   2017-12-17  / 2017/12/17===Date；　　（1：字符串转日期；2：按照给定的格式转）

@Configuration

@ConditionalOnWebApplication(

        type = ConditionalOnWebApplication.Type.SERVLET

)

@ConditionalOnClass({Servlet.class, DispatcherServlet.class, WebMvcConfigurer.class})

@ConditionalOnMissingBean({WebMvcConfigurationSupport.class})

@AutoConfigureOrder(-2147483638)

@AutoConfigureAfter({DispatcherServletAutoConfiguration.class, TaskExecutionAutoConfiguration.class, ValidationAutoConfiguration.class})

public class WebMvcAutoConfiguration {

    @Configuration

    @Import({org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.EnableWebMvcConfiguration.class})

    @EnableConfigurationProperties({WebMvcProperties.class, ResourceProperties.class})

    @Order(0)

    public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer, ResourceLoaderAware {

        private final ListableBeanFactory beanFactory;

        @Bean

        public FormattingConversionService mvcConversionService() {

            WebConversionService conversionService = new WebConversionService(this.mvcProperties.getDateFormat());

            this.addFormatters(conversionService);

            return conversionService;

        }

        protected void addFormatters(FormatterRegistry registry) {

            this.configurers.addFormatters(registry);

        }

        //添加格式化器

        public void addFormatters(FormatterRegistry registry) {

            //容器中符合Converter类型的bean都被格式化注册器FormatterRegistry注册进来

            Iterator var2 = this.getBeansOfType(Converter.class).iterator();

            while(var2.hasNext()) {

                Converter<?, ?> converter = (Converter)var2.next();

                registry.addConverter(converter);

            }

            //容器中符合GenericConverter类型的bean都被格式化注册器FormatterRegistry注册进来

            var2 = this.getBeansOfType(GenericConverter.class).iterator();

            while(var2.hasNext()) {

                GenericConverter converter = (GenericConverter)var2.next();

                registry.addConverter(converter);

            }

            //容器中符合Formatter类型的bean都被格式化注册器FormatterRegistry注册进来

            var2 = this.getBeansOfType(Formatter.class).iterator();

            while(var2.hasNext()) {

                Formatter<?> formatter = (Formatter)var2.next();

                registry.addFormatter(formatter);

            }

            /**

             *  从容器中获取所有从属于此类型的Bean

             *  自己添加的格式化器转换器，我们只需要放在容器中即可
*/

            private <T> Collection<T> getBeansOfType(Class<T> type) {

                return this.beanFactory.getBeansOfType(type).values();

            }

        }

    }

}

　　- HttpMessageConverter：SpringMVC用来转换Http请求和响应的；返回结果将　　User    ——》转化为　　Json；

　　- `HttpMessageConverters` 是从容器中确定；获取所有的HttpMessageConverter；

• 　　　　　　　　　　

• //@Configuration包含了@Component
  
  @Configuration
  
  public class WebMvcAutoConfiguration {
  
      public static class WebMvcAutoConfigurationAdapter implements WebMvcConfigurer, ResourceLoaderAware {
  
          private final ObjectProvider<HttpMessageConverters> messageConvertersProvider;
  
          //通过构造方法从容器中注入进来
  
          public WebMvcAutoConfigurationAdapter(ObjectProvider<HttpMessageConverters> messageConvertersProvider,其它参数) {
  
              this.messageConvertersProvider = messageConvertersProvider;
  
          ......
  
          }
  
      }
  
  }
  
  //@Configuration包含了@Component
  
  @Configuration
  
  public class HttpMessageConverters implements Iterable<HttpMessageConverter<?>> {
  
      private final List<HttpMessageConverter<?>> converters;
  
      //
  
      public HttpMessageConverters(HttpMessageConverter... additionalConverters) {
  
          this((Collection) Arrays.asList(additionalConverters));
  
      }
  
      //通过构造方法从容器中注入进来
  
      public HttpMessageConverters(Collection<HttpMessageConverter<?>> additionalConverters) {
  
          this(true, additionalConverters);
  
      }
  
  }

   自己给容器中添加HttpMessageConverter，只需要将自己的组件注册容器中（@Bean,@Component）

　　- Automatic registration of `MessageCodesResolver` (see below).定义错误代码生成规则

　　- Automatic use of a `ConfigurableWebBindingInitializer` bean (see below).

　　　　我们可以配置一个ConfigurableWebBindingInitializer来替换默认的；（添加到容器）

　　　　　　```初始化WebDataBinder；
　　　　　　```请求数据=====JavaBean；

If you want to keep Spring Boot MVC features and you want to add additional MVC configuration (interceptors, formatters, view controllers, and other features), you can add your own @Configuration class of type WebMvcConfigurer but without @EnableWebMvc. If you wish to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter, or ExceptionHandlerExceptionResolver, you can declare a WebMvcRegistrationsAdapter instance to provide such components.

If you want to take complete control of Spring MVC, you can add your own @Configuration annotated with @EnableWebMvc.

　总结：如何修改SpringBoot的默认配置？

​ 　　1）、SpringBoot在自动配置很多组件的时候，先看容器中有没有用户自己配置的（@Bean、@Component）如果有就用用户配置的，

　　　　如果没有，才自动配置；

　　　　如果有些组件可以有多个（ViewResolver）将用户配置的和自己默认的组合起来；