<servlet> <servlet-name>dispatcher</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <async-supported>false</async-supported> </servlet> <servlet-mapping> <servlet-name>dispatcher</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping>在javaweb项目中配置了DispatcherServlet的情况下，如果不进行额外配置的话，几乎所有的请求都会走这个servlet来处理，默认静态资源按路径是访问不到的会报404错误，下面讲一讲如何配置才能访问到静态资源，本文将介绍三种方法
1. 在java配置文件中配置DefaultServletHttpRequestHandler来进行处理
@Configuration @EnableWebMvc public class MyMvcConfigurer implements WebMvcConfigurer { @Override public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) { // tomcat默认处理静态资源的servlet名称为default,不指定也可以DefaultServletHttpRequestHandler.setServletContext会自动获取 // configurer.enable("default"); configurer.enable(); } }上述配置完成后org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport#defaultServletHandlerMapping 方法会生成一个类名为SimpleUrlHandlerMapping的bean，当其他handlerMapping无法处理请求时会接着调用SimpleUrlHandlerMapping对象进行处理
org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport#defaultServletHandlerMapping /** * Return a handler mapping ordered at Integer.MAX_VALUE with a mapped * default servlet handler. To configure "default" Servlet handling, * override {@link #configureDefaultServletHandling}. */ @Bean public HandlerMapping defaultServletHandlerMapping() { Assert.state(this.servletContext != null, "No ServletContext set"); DefaultServletHandlerConfigurer configurer = new DefaultServletHandlerConfigurer(this.servletContext); configureDefaultServletHandling(configurer); HandlerMapping handlerMapping = configurer.buildHandlerMapping(); return (handlerMapping != null ? handlerMapping : new EmptyHandlerMapping()); } org.springframework.web.servlet.config.annotation.DefaultServletHandlerConfigurer#buildHandlerMapping @Nullable protected SimpleUrlHandlerMapping buildHandlerMapping() { if (this.handler == null) { return null; } SimpleUrlHandlerMapping handlerMapping = new SimpleUrlHandlerMapping(); handlerMapping.setUrlMap(Collections.singletonMap("/**", this.handler)); handlerMapping.setOrder(Integer.MAX_VALUE); return handlerMapping; }SimpleUrlHandlerMapping中有一个urlMap属性，key为请求路径匹配模式串，'/**'能匹配所有的路径, value为handler匹配完成后会调用handler处理请求
下面这个方法主要用来匹配获取handler
org.springframework.web.servlet.handler.AbstractUrlHandlerMapping#getHandlerInternal
@Override @Nullable protected Object getHandlerInternal(HttpServletRequest request) throws Exception { // 请求静态资源 path=/zxq/static/login.png // 处理完lookupPath=/static/login.png String lookupPath = getUrlPathHelper().getLookupPathForRequest(request); Object handler = lookupHandler(lookupPath, request); if (handler == null) { // We need to care for the default handler directly, since we need to // expose the PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE for it as well. Object rawHandler = null; if ("/".equals(lookupPath)) { rawHandler = getRootHandler(); } if (rawHandler == null) { rawHandler = getDefaultHandler(); } if (rawHandler != null) { // Bean name or resolved handler? if (rawHandler instanceof String) { String handlerName = (String) rawHandler; rawHandler = obtainApplicationContext().getBean(handlerName); } validateHandler(rawHandler, request); handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null); } } if (handler != null && logger.isDebugEnabled()) { logger.debug("Mapping [" + lookupPath + "] to " + handler); } else if (handler == null && logger.isTraceEnabled()) { logger.trace("No handler mapping found for [" + lookupPath + "]"); } return handler; }org.springframework.web.servlet.handler.AbstractUrlHandlerMapping#lookupHandler
/** * Look up a handler instance for the given URL path. * <p>Supports direct matches, e.g. a registered "/test" matches "/test", * and various Ant-style pattern matches, e.g. a registered "/t*" matches * both "/test" and "/team". For details, see the AntPathMatcher class. * <p>Looks for the most exact pattern, where most exact is defined as * the longest path pattern. * @param urlPath the URL the bean is mapped to * @param request current HTTP request (to expose the path within the mapping to) * @return the associated handler instance, or {@code null} if not found * @see #exposePathWithinMapping * @see org.springframework.util.AntPathMatcher */ @Nullable protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception { // Direct match? // 精确匹配，是否有符合的handler // urlPath = /static/login.png Object handler = this.handlerMap.get(urlPath); if (handler != null) { // Bean name or resolved handler? if (handler instanceof String) { String handlerName = (String) handler; handler = obtainApplicationContext().getBean(handlerName); } validateHandler(handler, request); return buildPathExposingHandler(handler, urlPath, urlPath, null); } // Pattern match? // 路径匹配 List<String> matchingPatterns = new ArrayList<>(); for (String registeredPattern : this.handlerMap.keySet()) { if (getPathMatcher().match(registeredPattern, urlPath)) { matchingPatterns.add(registeredPattern); } else if (useTrailingSlashMatch()) { if (!registeredPattern.endsWith("/") && getPathMatcher().match(registeredPattern + "/", urlPath)) { matchingPatterns.add(registeredPattern + "/"); } } } String bestMatch = null; Comparator<String> patternComparator = getPathMatcher().getPatternComparator(urlPath); if (!matchingPatterns.isEmpty()) { matchingPatterns.sort(patternComparator); if (logger.isDebugEnabled()) { logger.debug("Matching patterns for request [" + urlPath + "] are " + matchingPatterns); } bestMatch = matchingPatterns.get(0); } // bestMatch = /static/** if (bestMatch != null) { handler = this.handlerMap.get(bestMatch); if (handler == null) { if (bestMatch.endsWith("/")) { handler = this.handlerMap.get(bestMatch.substring(0, bestMatch.length() - 1)); } if (handler == null) { throw new IllegalStateException( "Could not find handler for best pattern match [" + bestMatch + "]"); } } // Bean name or resolved handler? if (handler instanceof String) { String handlerName = (String) handler; handler = obtainApplicationContext().getBean(handlerName); } validateHandler(handler, request); // login.png String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestMatch, urlPath); // There might be multiple 'best patterns', let's make sure we have the correct URI template variables // for all of them Map<String, String> uriTemplateVariables = new LinkedHashMap<>(); for (String matchingPattern : matchingPatterns) { if (patternComparator.compare(bestMatch, matchingPattern) == 0) { Map<String, String> vars = getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath); Map<String, String> decodedVars = getUrlPathHelper().decodePathVariables(request, vars); uriTemplateVariables.putAll(decodedVars); } } if (logger.isDebugEnabled()) { logger.debug("URI Template variables for request [" + urlPath + "] are " + uriTemplateVariables); } // /static/** login.png return buildPathExposingHandler(handler, bestMatch, pathWithinMapping, uriTemplateVariables); } // No handler found... return null; }接着调用DefaultServletHttpRequestHandler的handleRequest方法处理请求，逻辑比较简单，获取请求转发器进行请求转发交给tomcat默认的servlet来进行处理
@Override public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { Assert.state(this.servletContext != null, "No ServletContext set"); RequestDispatcher rd = this.servletContext.getNamedDispatcher(this.defaultServletName); if (rd == null) { throw new IllegalStateException("A RequestDispatcher could not be located for the default servlet '" + this.defaultServletName + "'"); } rd.forward(request, response); }
2. 在java配置文件中配置ResourceHttpRequestHandler来进行处理
@Configuration @EnableWebMvc public class MyMvcConfigurer implements WebMvcConfigurer { @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/static/**").addResourceLocations("/static/"); } }和第一种配置几乎一样，其实只是换了一个handler类型来处理请求罢了
上述配置完成后org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport#resourceHandlerMapping 方法会生成一个类名为SimpleUrlHandlerMapping的bean，当其他handlerMapping无法处理请求时会接着调用SimpleUrlHandlerMapping对象进行处理
ResourceHttpRequestHandler比DefaultServletHttpRequestHandler的构建稍微复杂一点
org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport#resourceHandlerMapping /** * Return a handler mapping ordered at Integer.MAX_VALUE-1 with mapped * resource handlers. To configure resource handling, override * {@link #addResourceHandlers}. */ @Bean public HandlerMapping resourceHandlerMapping() { Assert.state(this.applicationContext != null, "No ApplicationContext set"); Assert.state(this.servletContext != null, "No ServletContext set"); ResourceHandlerRegistry registry = new ResourceHandlerRegistry(this.applicationContext, this.servletContext, mvcContentNegotiationManager(), mvcUrlPathHelper()); addResourceHandlers(registry); AbstractHandlerMapping handlerMapping = registry.getHandlerMapping(); if (handlerMapping != null) { handlerMapping.setPathMatcher(mvcPathMatcher()); handlerMapping.setUrlPathHelper(mvcUrlPathHelper()); handlerMapping.setInterceptors(getInterceptors()); handlerMapping.setCorsConfigurations(getCorsConfigurations()); } else { handlerMapping = new EmptyHandlerMapping(); } return handlerMapping; } org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry#getHandlerMapping /** * Return a handler mapping with the mapped resource handlers; or {@code null} in case * of no registrations. */ @Nullable protected AbstractHandlerMapping getHandlerMapping() { if (this.registrations.isEmpty()) { return null; } Map<String, HttpRequestHandler> urlMap = new LinkedHashMap<>(); for (ResourceHandlerRegistration registration : this.registrations) { for (String pathPattern : registration.getPathPatterns()) { ResourceHttpRequestHandler 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); } } SimpleUrlHandlerMapping handlerMapping = new SimpleUrlHandlerMapping(); handlerMapping.setOrder(order); handlerMapping.setUrlMap(urlMap); return handlerMapping; }之后也是调用SimpleUrlHandlerMapping相同的逻辑先根据请求路径匹配找到对应处理的handler，这里对应的是ResourceHttpRequestHandler之后调用handleRequest方法，原理是先根据请求的路径找到对应的资源文件，再获取资源文件的输入流写入到response响应中，源码如下：
org.springframework.web.servlet.resource.ResourceHttpRequestHandler#handleRequest
/** * Processes a resource request. * <p>Checks for the existence of the requested resource in the configured list of locations. * If the resource does not exist, a {@code 404} response will be returned to the client. * If the resource exists, the request will be checked for the presence of the * {@code Last-Modified} header, and its value will be compared against the last-modified * timestamp of the given resource, returning a {@code 304} status code if the * {@code Last-Modified} value is greater. If the resource is newer than the * {@code Last-Modified} value, or the header is not present, the content resource * of the resource will be written to the response with caching headers * set to expire one year in the future. */ @Override public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // For very general mappings (e.g. "/") we need to check 404 first // 根据请求的文件路径找到对应的资源文件 Resource resource = getResource(request); if (resource == null) { logger.trace("No matching resource found - returning 404"); response.sendError(HttpServletResponse.SC_NOT_FOUND); return; } if (HttpMethod.OPTIONS.matches(request.getMethod())) { response.setHeader("Allow", getAllowHeader()); return; } // Supported methods and required session // 校验支持的方法GET和HEAD 以及验证session是否必须 checkRequest(request); // Header phase if (new ServletWebRequest(request, response).checkNotModified(resource.lastModified())) { logger.trace("Resource not modified - returning 304"); return; } // Apply cache settings, if any // 可以根据设置的秒数设置缓存时间 cache-control:max-age=xxx prepareResponse(response); // Check the media type for the resource // 根据文件后缀去寻找 png -> image/png MediaType mediaType = getMediaType(request, resource); if (mediaType != null) { if (logger.isTraceEnabled()) { logger.trace("Determined media type '" + mediaType + "' for " + resource); } } else { if (logger.isTraceEnabled()) { logger.trace("No media type found for " + resource + " - not sending a content-type header"); } } // Content phase if (METHOD_HEAD.equals(request.getMethod())) { setHeaders(response, resource, mediaType); logger.trace("HEAD request - skipping content"); return; } ServletServerHttpResponse outputMessage = new ServletServerHttpResponse(response); if (request.getHeader(HttpHeaders.RANGE) == null) { Assert.state(this.resourceHttpMessageConverter != null, "Not initialized"); // 设置content-type、content-length等响应头 setHeaders(response, resource, mediaType); // 将文件流写入到response响应中 this.resourceHttpMessageConverter.write(resource, mediaType, outputMessage); } else { Assert.state(this.resourceRegionHttpMessageConverter != null, "Not initialized"); response.setHeader(HttpHeaders.ACCEPT_RANGES, "bytes"); ServletServerHttpRequest inputMessage = new ServletServerHttpRequest(request); try { List<HttpRange> httpRanges = inputMessage.getHeaders().getRange(); response.setStatus(HttpServletResponse.SC_PARTIAL_CONTENT); this.resourceRegionHttpMessageConverter.write( HttpRange.toResourceRegions(httpRanges, resource), mediaType, outputMessage); } catch (IllegalArgumentException ex) { response.setHeader("Content-Range", "bytes */" + resource.contentLength()); response.sendError(HttpServletResponse.SC_REQUESTED_RANGE_NOT_SATISFIABLE); } } }
3. web.xml配置servlet映射
原理可以参考上一篇文章
<servlet-mapping> <servlet-name>default</servlet-name> <url-pattern>/static/*</url-pattern> </servlet-mapping>将带有/static/xxx 路径的请求直接交给tomcat默认的servlet去进行处理
最后
完成上述的一种配置后就能访问到我们的静态资源了，请求路径http://localhost:8082/zxq/static/login.png
补充
若配置了拦截器且使用第二种方法，拦截器也会对静态资源进行拦截，若不需要拦截还需要进行额外的配置去除比较麻烦
第一种方法用dispatcherServlet拦截所有的请求再将请求交给tomcat默认的servlet处理，性能上有所消耗，拦截器不过滤
第二种方法拦截器会进行过滤若需要过滤的路径较多配置麻烦
第三种方法直接用tomcat默认的servlet进行处理，但静态资源路径有多个时配置也比较麻烦
综上所述，根据自己项目的情况选择哪一种方法~
@Configuration @EnableWebMvc public class MyMvcConfigurer implements WebMvcConfigurer { @Resource private CustomInterceptor customInterceptor; @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(customInterceptor) .addPathPatterns("/**") .excludePathPatterns("/static/**"); } // @Override // public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) { // // tomcat默认处理静态资源的servlet名称为default,不指定也可以DefaultServletHttpRequestHandler.setServletContext会自动获取 //// configurer.enable("default"); // configurer.enable(); // } @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/static/**").addResourceLocations("/static/"); } }
![洛谷 P11345 [KTSC 2023 R2] 基地简化 题解](http://www.itfaba.com/wp-content/themes/kemi/timthumb.php?src=http://www.itfaba.com/wp-content/themes/kemi/img/random/3.jpg&w=218&h=124&zc=1)
