SpringMvc @RequestMapping原理-白红宇的个人博客

SpringMvc @RequestMapping原理

发布日期：2021-05-16 13:48:21 浏览次数：19 分类：博客文章

本文共 6684 字，大约阅读时间需要 22 分钟。

讲这个之前，我们得先知道在SpringMvc启动时，会加载所有的Bean类，就是加了@Controller，@Component等组件标识的类，然后会把@RequestMapping的方法也加入到一个集合。放入到上下文环境中。

发起请求后的执行流程是：检查request类型-->获取匹配的Handlemethod-->查找拦截器-->组成HandlerExecutionChain执行链-->获取方法执行链对象的适配器（HandlerAdapter）-->然后反射执行业务方法。

有一个大概的了解之后，开始源码分析：

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {        HttpServletRequest processedRequest = request;        HandlerExecutionChain mappedHandler = null;        boolean multipartRequestParsed = false;        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);        try {            ModelAndView mv = null;            Exception dispatchException = null;            try {                processedRequest = checkMultipart(request);                multipartRequestParsed = processedRequest != request;                // Determine handler for the current request. 　　　　　　　　　　//获取匹配的执行链                  mappedHandler = getHandler(processedRequest);                if (mappedHandler == null || mappedHandler.getHandler() == null) {                    noHandlerFound(processedRequest, response);                    return;                }                // Determine handler adapter for the current request.                 //根据匹配到的执行链对象，获取合适的适配器                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());                // Process last-modified header, if supported by the handler.                String method = request.getMethod();                boolean isGet = "GET".equals(method);                if (isGet || "HEAD".equals(method)) {                    long lastModified = ha.getLastModified(request, mappedHandler.getHandler());                    if (logger.isDebugEnabled()) {                        String requestUri = urlPathHelper.getRequestUri(request);                        logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);                    }                    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {                        return;                    }                }                      if (!mappedHandler.applyPreHandle(processedRequest, response)) {                    return;                }                try {                    // Actually invoke the handler. 　　　　　　　　　　　　//在这里面反射执行业务方法                    mv = ha.handle(processedRequest, response, mappedHandler.getHandler());                }                finally {                    if (asyncManager.isConcurrentHandlingStarted()) {                        return;                    }                }                applyDefaultViewName(request, mv);                mappedHandler.applyPostHandle(processedRequest, response, mv);            }            catch (Exception ex) {                dispatchException = ex;            }            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);        }        catch (Exception ex) {            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);        }        catch (Error err) {            triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);        }        finally {            if (asyncManager.isConcurrentHandlingStarted()) {                // Instead of postHandle and afterCompletion                mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);                return;            }            // Clean up any resources used by a multipart request.            if (multipartRequestParsed) {                cleanupMultipart(processedRequest);            }        }    }

从标红部分点进去，到AbstractHandlerMethodAdapter类的handle方法-->RequestMappingHandlerAdapter类的handleInternal方法-->RequestMappingHandlerAdapter类的invokeHandleMethod

-->RequestMappingHandlerAdapter类的invokeAndHandle-->ServletInvocableHandlerMethod类的invokeForRequest-->InvocableHandlerMethod类的invokeForRequest。该方法代码如下：

public final Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer,            Object... providedArgs) throws Exception {        Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);        if (logger.isTraceEnabled()) {            StringBuilder sb = new StringBuilder("Invoking [");            sb.append(this.getBeanType().getSimpleName()).append(".");            sb.append(getMethod().getName()).append("] method with arguments ");            sb.append(Arrays.asList(args));            logger.trace(sb.toString());        } 　　　　　//执行方法        Object returnValue = invoke(args);        if (logger.isTraceEnabled()) {            logger.trace("Method [" + getMethod().getName() + "] returned [" + returnValue + "]");        }        return returnValue;    }

然后就可以执行方法了。需要注意的是匹配方法时，根据@RequestMapping里面的value路径来匹配的，如果匹配到的有多个，如你配置了通配符，也配置了精确配置，他都会匹配到放在一个集合中，根据规则排序，然后取集合的第一个元素。有兴趣的可以看看这个排序的规则，理论上肯定是路径越精确的会优先，具体代码实现如下：

protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {        List
    
      matches = new ArrayList
     
      ();        List
      
        directPathMatches = this.urlMap.get(lookupPath);        if (directPathMatches != null) {            addMatchingMappings(directPathMatches, matches, request);        }        if (matches.isEmpty()) {            // No choice but to go through all mappings            addMatchingMappings(this.handlerMethods.keySet(), matches, request);        }        if (!matches.isEmpty()) { 　　　　　　  //排序规则            Comparator
       
         comparator = new MatchComparator(getMappingComparator(request));            //进行排序            Collections.sort(matches, comparator);            if (logger.isTraceEnabled()) {                logger.trace("Found " + matches.size() + " matching mapping(s) for [" + lookupPath + "] : " + matches);            }            Match bestMatch = matches.get(0);            if (matches.size() > 1) {                Match secondBestMatch = matches.get(1);                if (comparator.compare(bestMatch, secondBestMatch) == 0) {                    Method m1 = bestMatch.handlerMethod.getMethod();                    Method m2 = secondBestMatch.handlerMethod.getMethod();                    throw new IllegalStateException(                            "Ambiguous handler methods mapped for HTTP path '" + request.getRequestURL() + "': {" +                            m1 + ", " + m2 + "}");                }            }            handleMatch(bestMatch.mapping, lookupPath, request);            return bestMatch.handlerMethod;        }        else {            return handleNoMatch(handlerMethods.keySet(), lookupPath, request);        }    }

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