SpringMvc @RequestMapping原理

我会带着你远行 2022-05-08 00:46 229阅读 0赞

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：

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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);
                }
            }
        }

![复制代码][copycode.gif]

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：

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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;
        }

![复制代码][copycode.gif]

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：

![复制代码][copycode.gif]

protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
            List<Match> matches = new ArrayList<Match>();
    
            List<T> 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<Match> 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);
            }
        }

![复制代码][copycode.gif]

[copycode.gif]: /images/20220508/bd180190fe0e40e9a7b2d63212b5d014.png