2023-09-14  阅读(153)
原文作者:王伟王胖胖 原文地址: https://blog.csdn.net/wangwei19871103/article/details/105567054

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EnableWebMvcConfigurationresourceHandlerMapping调用的时候:

202309142304305861.png

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:

202309142304314972.png
然后在他在初始化之前处理的setApplicationContext方法中注册了两个映射:

202309142304327173.png
注册到handlerMap中:

202309142304335374.png
log信息也有:

202309142304346095.png

实验

比如我直接请求resources\static\test.html

202309142304355616.png
直接在浏览器

202309142304361747.png

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。

202309142304366828.png
最后还会加一个跨域的拦截器:

202309142304374729.png

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 {
    			...
    			}
    		}
    	}

下篇说怎么获取资源和写出去的。

好了,今天就到这里了,希望对学习理解有帮助,大神看见勿喷,仅为自己的学习理解,能力有限,请多包涵。

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