image

• 用户发送请求至前端控制器DispatcherServlet；

• DispatcherServlet收到请求后，调用HandlerMapping处理器映射器，请求获取Handle；

• 处理器映射器根据请求url找到具体的处理器，生成处理器对象及处理器拦截器(如果有则生成)一并返回给DispatcherServlet；

• DispatcherServlet 调用 HandlerAdapter处理器适配器；

• HandlerAdapter 经过适配调用 具体处理器(Handler，也叫后端控制器)；

• Handler执行完成返回ModelAndView；

• HandlerAdapter将Handler执行结果ModelAndView返回给DispatcherServlet；

• DispatcherServlet将ModelAndView传给ViewResolver视图解析器进行解析；

• ViewResolver解析后返回具体View；

• DispatcherServlet对View进行渲染视图（即将模型数据填充至视图中）

• DispatcherServlet响应用户。

step1 封装数据并进入doDispatch方法 (已省略部分代码)
DispatcherServlet.java

protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
        // Keep a snapshot of the request attributes in case of an include,
        // to be able to restore the original attributes after the include.
        Map<String, Object> attributesSnapshot = null;
        if (WebUtils.isIncludeRequest(request)) {
            attributesSnapshot = new HashMap<String, Object>();
            Enumeration<?> attrNames = request.getAttributeNames();
            while (attrNames.hasMoreElements()) {
                String attrName = (String) attrNames.nextElement();
                if (this.cleanupAfterInclude || attrName.startsWith("org.springframework.web.servlet")) {
                    attributesSnapshot.put(attrName, request.getAttribute(attrName));
                }
            }
        }

        // Make framework objects available to handlers and view objects.
        request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
        request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
        request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
        request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());

        FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
        if (inputFlashMap != null) {
            request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
        }
        request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
        request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
        doDispatch(request, response);    --------------重点
    }

step2 找hanlder 找hanlerAdapter invoke方法

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.  根据request得到handler和拦截器组成的链 具体看step2.1
            mappedHandler = getHandler(processedRequest); 
            // Determine handler adapter for the current request. 根据handler得到handlerAdapter
            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()) {
                    logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
                }
                if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
                    return;
                }
            }

            if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                return;
            }

            // Actually invoke the handler. 执行方法并返回modleAndView
            mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

            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
            if (mappedHandler != null) {
                mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
            }
        }
        else {
            // Clean up any resources used by a multipart request.
            if (multipartRequestParsed) {
                cleanupMultipart(processedRequest);
            }
        }
    }
}

step2.1 关于如何得到handler

得到handler过程.PNG

细节：handlerMappings是什么时候被赋值的呢？
是在dispatcher的initHandlerMappings() 从applicationcontext中读取并赋值 本地debug时发现有3个mapping(RequestMappingHandlerMapping
/BeanNameUrlHandlerMapping/SimpleUrlHandlerMapping)

DispatcherServler.java

protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        for (HandlerMapping hm : this.handlerMappings) {
                HandlerExecutionChain handler = hm.getHandler(request);
                if (handler != null) {
                        return handler;
                }
        }
        return null;
}

AbstractHandlerMapping.java

public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    Object handler = getHandlerInternal(request); 具体源码在下面
    if (handler == null) {
        handler = getDefaultHandler();
    }
    if (handler == null) {
        return null;
    }
    // Bean name or resolved handler?
    if (handler instanceof String) {
        String handlerName = (String) handler;
        handler = getApplicationContext().getBean(handlerName);
    }
    得到handler再去得handler链(加一加拦截器)
    return getHandlerExecutionChain(handler, request);
}

protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
    String lookupPath = getUrlPathHelper().getLookupPathForRequest(request); 得到URL
    查找当前请求的最佳匹配处理程序方法。如果找到多个匹配项，则选择最佳匹配项。
    HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
    return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
 }

protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
    HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
            (HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
    chain.addInterceptors(getAdaptedInterceptors());

    String lookupPath = this.urlPathHelper.getLookupPathForRequest(request); //得到请求的相对URL
    for (MappedInterceptor mappedInterceptor : this.mappedInterceptors) {
        //添加拦截器
        if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
            chain.addInterceptor(mappedInterceptor.getInterceptor());
        }
    }
    return chain;
}