WebMvc自动配置流程讲解

WebMvc自动配置流程讲解

原理分析

• 启动springMvc内置的视图解析器ContentNegotiatingViewResolver和BeanNameViewResolver
  • ContentNegotiatingViewResolver ：并不会解析视图本身，而是委托其他的视图解析器进行解析
    • 所有的视图解析器，都会根据返回的视图名称进行解析视图

@Override
@Nullable
public View resolveViewName(String viewName, Locale locale) throws Exception {
    RequestAttributes attrs = RequestContextHolder.getRequestAttributes();
    Assert.state(attrs instanceof ServletRequestAttributes, "No current ServletRequestAttributes");
    List<MediaType> requestedMediaTypes = getMediaTypes(((ServletRequestAttributes) attrs).getRequest());
    if (requestedMediaTypes != null) {
        // 获得所有匹配的视图
       List<View> candidateViews = getCandidateViews(viewName, locale, requestedMediaTypes);
        // 获取最终的视图
       View bestView = getBestView(candidateViews, requestedMediaTypes, attrs);
       if (bestView != null) {
          return bestView;
       }
    }

委派给其他解析器进行解析

@Override
protected void initServletContext(ServletContext servletContext) {
    Collection<ViewResolver> matchingBeans =
          BeanFactoryUtils.beansOfTypeIncludingAncestors(obtainApplicationContext(), ViewResolver.class).values();
    if (this.viewResolvers == null) {
       this.viewResolvers = new ArrayList<>(matchingBeans.size());
       for (ViewResolver viewResolver : matchingBeans) {
          if (this != viewResolver) {
             this.viewResolvers.add(viewResolver);
          }
       }
    }

由以上的代码可以得出结论，它是从Spring IOC容器中获得viewResolver，我们可以自己定制一个viewResolver，ContentNegotiatingViewResolver也会帮我们委派解析

• BeanNameViewResolver

  • 根据handler方法返回的视图名称 对应到具体视图并解析（定义一个相同名称的类，此类继承一个view（abstractXlsView等等）的接口去生成一个视图）

• 支持提供静态资源，包括对WebJars的支持

  • WebJars将静态资源放在jar包中进行访问

  • 以前要访问jpg、css、js等这些静态资源文件，需要在web.xml配置，在springboot中不需要配置，只需要放到指定的文件夹中就可以读取出来（约定大于配置）

    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        if (!this.resourceProperties.isAddMappings()) {
           logger.debug("Default resource handling disabled");
           return;
        }
        addResourceHandler(registry, "/webjars/**", "classpath:/META-INF/resources/webjars/");
        addResourceHandler(registry, this.mvcProperties.getStaticPathPattern(), (registration) -> {
           registration.addResourceLocations(this.resourceProperties.getStaticLocations());
           if (this.servletContext != null) {
              ServletContextResource resource = new ServletContextResource(this.servletContext, SERVLET_LOCATION);
              registration.addResourceLocations(resource);
           }
        });
    }
    

    为什么我们访问http://localhost:8080/image/timssg.jpg也可以访问到图片呢？

  public static class Resources {
  
      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;
  

  • 上述代码表示，当图片位于上面的文件中也是可以被读取出来的

• 自动注册Converter,GenericConverter和FormatterBean类

• 支持HttpMessageConverters

  • HttpMessageConverters负责http请求和响应的报文处理

• 自动注册MessageCodesResolver

  • 修改错误下的格式转换出错类型转换出错的错误代码

• 静态index.html支持

  • 在springboot中可以直接返回html的视图

  • 因为在自动WebMvcAutoConfiguration配置类配置

  • 所以就可以通过在配置文件中完成配置

  @Bean
  @ConditionalOnMissingBean
  public InternalResourceViewResolver defaultViewResolver() {
      InternalResourceViewResolver resolver = new InternalResourceViewResolver();
      resolver.setPrefix(this.mvcProperties.getView().getPrefix());
      resolver.setSuffix(this.mvcProperties.getView().getSuffix());
      return resolver;
  }
  

  @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 {
  
      /**
       * The default Spring MVC view prefix.
       */
      public static final String DEFAULT_PREFIX = "";
  
      /**
       * The default Spring MVC view suffix.
       */
      public static final String DEFAULT_SUFFIX = "";
  

• 自动使用ConfigurableWebingingInitializer bean