静态资源如何访问

可以直接访问静态资源，因为有SimpleUrlHandlerMapping处理。

EnableWebMvcConfiguration的resourceHandlerMapping

自动配置EnableWebMvcConfiguration的resourceHandlerMapping调用的时候：

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ResourceHandlerRegistry的resourceHandlerMapping

最后创建一个SimpleUrlHandlerMapping，里面有两个映射，定义了两种资源路径：

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然后在他在初始化之前处理的setApplicationContext方法中注册了两个映射：

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注册到handlerMap中：

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log信息也有：

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实验

比如我直接请求resources\static\test.html：

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直接在浏览器

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AbstractUrlHandlerMapping的lookupHandler

我们来看看原理，获取处理器映射器的时候就到这个方法里，其实就是进行uri的匹配，匹配到了再解析uri参数，最后封装成执行链加入拦截器返回。

@Nullable
    protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {
        // 直接能匹配上
        Object handler = this.handlerMap.get(urlPath);
        if (handler != null) {//如果存在的话
            // Bean name or resolved handler?
            if (handler instanceof String) {//只是名字的话要实例化
                String handlerName = (String) handler;
                handler = obtainApplicationContext().getBean(handlerName);
            }
            validateHandler(handler, request);
            return buildPathExposingHandler(handler, urlPath, urlPath, null);
        }

        // Pattern match? uri模式匹配
        List<String> matchingPatterns = new ArrayList<>();
        for (String registeredPattern : this.handlerMap.keySet()) {//遍历进行匹配
            if (getPathMatcher().match(registeredPattern, urlPath)) {
                matchingPatterns.add(registeredPattern);//匹配上就添加进去
            }
            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()) {//不为空的话排序
            matchingPatterns.sort(patternComparator);
            if (logger.isTraceEnabled() && matchingPatterns.size() > 1) {
                logger.trace("Matching patterns " + matchingPatterns);
            }
            bestMatch = matchingPatterns.get(0);//取第一个
        }
        if (bestMatch != null) {//存在就获取对应的处理器
            handler = this.handlerMap.get(bestMatch);
            if (handler == null) {
                if (bestMatch.endsWith("/")) {//如果以/结尾的话就把/去掉再看有没映射的处理器
                    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) {//处理器只是名字的话要实例化
                String handlerName = (String) handler;
                handler = obtainApplicationContext().getBean(handlerName);
            }
            validateHandler(handler, request);
            String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestMatch, urlPath);//取出匹配的资源，出掉最开始的/

            // uri参数，比如restful风格的
            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.isTraceEnabled() && uriTemplateVariables.size() > 0) {
                logger.trace("URI variables " + uriTemplateVariables);
            }
            return buildPathExposingHandler(handler, bestMatch, pathWithinMapping, uriTemplateVariables);//封装执行链加入拦截器一起返回
        }

        // No handler found...
        return null;
    }

buildPathExposingHandler

创建执行链，然后加入一个PathExposingHandlerInterceptor拦截器，如果有uri参数的话还要加入UriTemplateVariablesHandlerInterceptor拦截器，其实就是设置一些请求属性，暴露给请求。

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最后还会加一个跨域的拦截器：

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ResourceHttpRequestHandler的handleRequest执行处理器

重点就是获取资源，然后写出去。

@Override
    public void handleRequest(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        // 获取资源
        Resource resource = getResource(request);
        if (resource == null) {//找不到
            logger.debug("Resource not found");
            response.sendError(HttpServletResponse.SC_NOT_FOUND);
            return;
        }
        ...
        // 获取资源媒体类型
        MediaType mediaType = getMediaType(request, resource);
        ...
        ServletServerHttpResponse outputMessage = new ServletServerHttpResponse(response);
        if (request.getHeader(HttpHeaders.RANGE) == null) {
            Assert.state(this.resourceHttpMessageConverter != null, "Not initialized");
            setHeaders(response, resource, mediaType);//设置头信息
            this.resourceHttpMessageConverter.write(resource, mediaType, outputMessage);//写出去
        }
        else {
            ...
            }
        }
    }