SpringMVC DispatcherServlet源码(6) 完结 静态资源原理

阅读源码，分析静态资源处理器相关组件：

1. 使用SimpleUrlHandlerMapping管理url -> 处理器映射关系
2. spring mvc使用WebMvcConfigurationSupport注入SimpleUrlHandlerMapping组件
3. DelegatingWebMvcConfiguration可以使用WebMvcConfigurer的配置静态资源url pattern
4. spring boot使用EnableWebMvcConfiguration类读取配置参数，然后ResourceHandlerRegistry添加静态资源url pattern
5. SimpleUrlHandlerMapping中封装ResourceHttpRequestHandler对象作为请求处理器
6. HttpRequestHandlerAdapter支持HttpRequestHandler类型的请求处理器

本文将对上述6点内容展开分析。

注入HandlerMapping

WebMvcConfigurationSupport注入SimpleUrlHandlerMapping组件

在spring mvc中，静态资源也使用HandlerMapping管理映射关系，只是使用的实现类不一样：

• 业务请求使用的HandlerMapping实现类是RequestMappingHandlerMapping类
• 静态资源使用的HandlerMapping实现类是SimpleUrlHandlerMapping类

注入SimpleUrlHandlerMapping对象的入口在WebMvcConfigurationSupport的resourceHandlerMapping方法中：

// Return a handler mapping ordered at Integer.MAX_VALUE-1 with mapped resource handlers.
// To configure resource handling, override addResourceHandlers.
@Bean
public HandlerMapping resourceHandlerMapping(@Qualifier("mvcUrlPathHelper") UrlPathHelper urlPathHelper,@Qualifier("mvcPathMatcher") PathMatcher pathMatcher,@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,@Qualifier("mvcConversionService") FormattingConversionService conversionService,@Qualifier("mvcResourceUrlProvider") ResourceUrlProvider resourceUrlProvider) {ResourceHandlerRegistry registry = new ResourceHandlerRegistry(this.applicationContext,this.servletContext, contentNegotiationManager, urlPathHelper);// Add resource handlers for serving static resources// 这是一个抽象方法，用于向registry添加静态资源路径pattern// * 一个是spring mvc的DelegatingWebMvcConfiguration类// * 一个是spring boot的WebMvcAutoConfiguration.EnableWebMvcConfiguration类// * 两者的本质就是使用registry.addResourceHandler添加静态资源路径patternaddResourceHandlers(registry);// 根据添加的静态资源路径pattern创建HandlerMapping// 里面创建的是SimpleUrlHandlerMapping类型对象AbstractHandlerMapping handlerMapping = registry.getHandlerMapping();if (handlerMapping == null) {return null;}handlerMapping.setPathMatcher(pathMatcher);handlerMapping.setUrlPathHelper(urlPathHelper);handlerMapping.setInterceptors(getInterceptors(conversionService, resourceUrlProvider));handlerMapping.setCorsConfigurations(getCorsConfigurations());return handlerMapping;
}

下文将介绍：

• addResourceHandlers的实现
• registry创建SimpleUrlHandlerMapping的方式

DelegatingWebMvcConfiguration的addResourceHandlers方法

protected void addResourceHandlers(ResourceHandlerRegistry registry) {this.configurers.addResourceHandlers(registry);
}

configurers是WebMvcConfigurerComposite对象，内部封装这容器里面的所有WebMvcConfigurer组件集：

private final WebMvcConfigurerComposite configurers = new WebMvcConfigurerComposite();@Autowired(required = false)
public void setConfigurers(List<WebMvcConfigurer> configurers) {if (!CollectionUtils.isEmpty(configurers)) {this.configurers.addWebMvcConfigurers(configurers);}
}

当调用this.configurers.addResourceHandlers时，WebMvcConfigurerComposite又会通过WebMvcConfigurer添加静态资源路径pattern：

public void addResourceHandlers(ResourceHandlerRegistry registry) {for (WebMvcConfigurer delegate : this.delegates) {// 这里通过WebMvcConfigurer调用扩展逻辑，添加静态资源路径patterndelegate.addResourceHandlers(registry);}
}

例如：

@Component
public class AppConfig implements WebMvcConfigurer {// ...@Overridepublic void addResourceHandlers(ResourceHandlerRegistry registry) {registry.addResourceHandler("/static/**").addResourceLocations("/static/");}// ...
}

EnableWebMvcConfiguration的addResourceHandlers方法

protected void addResourceHandlers(ResourceHandlerRegistry registry) {// 调用父类方法，也就是使用WebMvcConfigurer添加静态资源patternsuper.addResourceHandlers(registry);if (!this.resourceProperties.isAddMappings()) {return;}addResourceHandler(registry, "/webjars/**", "classpath:/META-INF/resources/webjars/");// spring boot的spring.mvc.staticPathPattern配置参数// spring boot的spring.resources.staticLocations配置参数addResourceHandler(registry, this.mvcProperties.getStaticPathPattern(),this.resourceProperties.getStaticLocations());
}private void addResourceHandler(ResourceHandlerRegistry registry, String pattern, String... locations) {if (registry.hasMappingForPattern(pattern)) {return;}// 添加静态资源patternResourceHandlerRegistration registration = registry.addResourceHandler(pattern);registration.addResourceLocations(locations);registration.setCachePeriod(getSeconds(this.resourceProperties.getCache().getPeriod()));registration.setCacheControl(this.resourceProperties.getCache().getCachecontrol().toHttpCacheControl());customizeResourceHandlerRegistration(registration);this.autoConfiguredResourceHandlers.add(pattern);
}

WebMvcConfigurer接口

定义callback方法，Spring MVC通过这些方法扩展组件：

public interface WebMvcConfigurer {// 配置PathMatchConfigurerdefault void configurePathMatch(PathMatchConfigurer configurer) {}// Configure content negotiation optionsdefault void configureContentNegotiation(ContentNegotiationConfigurer configurer) {}// Configure asynchronous request handling optionsdefault void configureAsyncSupport(AsyncSupportConfigurer configurer) {}// 配置DefaultServletHttpRequestHandlerdefault void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {}// Add Converters and Formatters in addition to the ones registered by defaultdefault void addFormatters(FormatterRegistry registry) {}// 添加拦截器default void addInterceptors(InterceptorRegistry registry) {}// 添加静态资源处理器default void addResourceHandlers(ResourceHandlerRegistry registry) {}// cors配置default void addCorsMappings(CorsRegistry registry) {}// 添加ViewControllerdefault void addViewControllers(ViewControllerRegistry registry) {}// 配置ViewResolverdefault void configureViewResolvers(ViewResolverRegistry registry) {}// 添加参数解析器default void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {}// 添加返回值处理器default void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> handlers) {}// 配置消息转换器default void configureMessageConverters(List<HttpMessageConverter<?>> converters) {}// 扩展消息转换器default void extendMessageConverters(List<HttpMessageConverter<?>> converters) {}// 配置异常处理器default void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {}// 扩展异常处理器default void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {}
}

创建SimpleUrlHandlerMapping对象

protected AbstractHandlerMapping getHandlerMapping() {Map<String, HttpRequestHandler> urlMap = new LinkedHashMap<>();for (ResourceHandlerRegistration registration : this.registrations) {for (String pathPattern : registration.getPathPatterns()) {// * 请注意这里使用的是ResourceHttpRequestHandlerResourceHttpRequestHandler handler = registration.getRequestHandler();if (this.pathHelper != null) {handler.setUrlPathHelper(this.pathHelper);}if (this.contentNegotiationManager != null) {handler.setContentNegotiationManager(this.contentNegotiationManager);}handler.setServletContext(this.servletContext);handler.setApplicationContext(this.applicationContext);try {handler.afterPropertiesSet();} catch (Throwable ex) {throw new BeanInitializationException("Failed to init ResourceHttpRequestHandler", ex);}urlMap.put(pathPattern, handler);}}// 创建SimpleUrlHandlerMappingreturn new SimpleUrlHandlerMapping(urlMap, this.order);
}

SimpleUrlHandlerMapping类

private final Map<String, Object> handlerMap = new LinkedHashMap<>();

使用一个Map<String, Object>管理url pattern -> 处理器对象的映射关系。

从上文可以知道，静态资源映射使用的是ResourceHttpRequestHandler类型的处理器。

ResourceHttpRequestHandler类

这个类实现了HttpRequestHandler接口：

@FunctionalInterface
public interface HttpRequestHandler {void handleRequest(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException;
}

ResourceHttpRequestHandler的代码实现：

public void handleRequest(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {Resource resource = getResource(request);if (resource == null) {// 404response.sendError(HttpServletResponse.SC_NOT_FOUND);return;}if (HttpMethod.OPTIONS.matches(request.getMethod())) {response.setHeader("Allow", getAllowHeader());return;}// Supported methods and required sessioncheckRequest(request);// Header phaseif (new ServletWebRequest(request, response).checkNotModified(resource.lastModified())) {return;}// Apply cache settings, if anyprepareResponse(response);// Check the media type for the resourceMediaType mediaType = getMediaType(request, resource);setHeaders(response, resource, mediaType);// Content phaseServletServerHttpResponse outputMessage = new ServletServerHttpResponse(response);// 不是range请求if (request.getHeader(HttpHeaders.RANGE) == null) {// 把资源写出去this.resourceHttpMessageConverter.write(resource, mediaType, outputMessage);} else {ServletServerHttpRequest inputMessage = new ServletServerHttpRequest(request);try {// range请求List<HttpRange> httpRanges = inputMessage.getHeaders().getRange();response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT);// 把资源写出去this.resourceRegionHttpMessageConverter.write(HttpRange.toResourceRegions(httpRanges, resource), mediaType, outputMessage);} catch (IllegalArgumentException ex) {response.setHeader(HttpHeaders.CONTENT_RANGE, "bytes */" + resource.contentLength());response.sendError(HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE);}}
}

HttpRequestHandlerAdapter类

前面的文章已经介绍，HttpRequestHandlerAdapter负责处理HttpRequestHandler类型的处理器：

public class HttpRequestHandlerAdapter implements HandlerAdapter {@Overridepublic boolean supports(Object handler) {return (handler instanceof HttpRequestHandler);}@Override@Nullablepublic ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception {((HttpRequestHandler) handler).handleRequest(request, response);return null;}@Overridepublic long getLastModified(HttpServletRequest request, Object handler) {if (handler instanceof LastModified) {return ((LastModified) handler).getLastModified(request);}return -1L;}
}

这个组件在WebMvcConfigurationSupport的httpRequestHandlerAdapter方法注入。

小结

至此，我们用了6篇文章详细介绍了SpringMVC DispatcherServlet的注册、请求转发、消息转换等内容，DispatcherServlet的源码分析到此可以结束了。