springmvc执行流程 源码分析

浏览器发送一个请求给DispatcherServlet （在doDispatch(request, response)中）；DispatcherServlet将请求交给HandleMapping 获取处理器执行链；DispatcherServlet获得执行链中的handle；遍历所有处理器适配器，获得支持handle的具体的适配器；处理器执行链执行前置处理（返回false就不再往下执行）；然后由DispatcherServlet将请求、响应和handle交给处理器适配器处理，HandleAdapter执行控制器Controller中具体的方法返回ModelAndView；处理器执行链执行后置处理；通过试图解析器解析准确试图，将模型数组放到request域中渲染试图；将试图返回前端页面。

HandlerMapping接口就一个作用：根据request获取handle和拦截器数组。

---

概念理解：

handler在这里，是指包含了我们请求的Controller类和 url映射的Method方法的对象。

一个控制器Controller中有内部N个方法== N个Handler

M个控制器=M×N个Handler

M×N个Hanlder存放在handlerMappings中

 

 

public interface HandlerMapping {

 HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;

}

HandlerExecutionChain包含一个handle和一个拦截器数组。

public class HandlerExecutionChain {

 private final Object handler;

 private HandlerInterceptor[] interceptors;

~

}

public class HttpRequestHandlerAdapter implements HandlerAdapter {

 @Override
 public boolean supports(Object handler) {
  return (handler instanceof HttpRequestHandler);
 }

 @Override
 public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
   throws Exception {

  ((HttpRequestHandler) handler).handleRequest(request, response);
  return null;
 }

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进入DispatcherServlet 执行onRefresh，然后执行初始化方法initStrategies。然后调用doService——>doDispatch。

根据继承关系执行Servlet的步骤：

init...............initStrategies

service...........doService

/**
     * This implementation calls {@link #initStrategies}.
     */
    @Override
    protected void onRefresh(ApplicationContext context) {
        initStrategies(context);
    }

    /**
     * Initialize the strategy objects that this servlet uses.
     * <p>May be overridden in subclasses in order to initialize further strategy objects.
     */
    protected void initStrategies(ApplicationContext context) {
        initMultipartResolver(context);
        initLocaleResolver(context);
        initThemeResolver(context);
        initHandlerMappings(context);
        initHandlerAdapters(context);
        initHandlerExceptionResolvers(context);
        initRequestToViewNameTranslator(context);
        initViewResolvers(context);
        initFlashMapManager(context);
    }

/**
     * Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch}
     * for the actual dispatching.
     */
    @Override
    protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
        if (logger.isDebugEnabled()) {
            String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
            logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
                    " processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]");
        }

        // Keep a snapshot of the request attributes in case of an include,
        // to be able to restore the original attributes after the include.
　　　　 // 保存request中的所有属性

        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(DEFAULT_STRATEGIES_PREFIX)) {
                    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);

        try {
            doDispatch(request, response);//处理用户请求
        }
        finally {
            if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
                // Restore the original attribute snapshot, in case of an include.
                if (attributesSnapshot != null) {
                    restoreAttributesAfterInclude(request, attributesSnapshot);
                }
            }
        }
    }

/**
     * Process the actual dispatching to the handler.
     * <p>The handler will be obtained by applying the servlet's HandlerMappings in order.
     * The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters
     * to find the first that supports the handler class.
     * <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers
     * themselves to decide which methods are acceptable.
     * @param request current HTTP request
     * @param response current HTTP response
     * @throws Exception in case of any kind of processing failure
     */
    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);

                
　　　　　　　　　 // 遍历handlerMappings获取HandlerExecutionChain实例(handle和HandlerInterceptor[])
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null || mappedHandler.getHandler() == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                // Determine handler adapter for the current request.
　　　　　　　　　 // 通过 处理器执行链 匹配 处理器适配器 实例
　　　　　　　　　 // 获取 处理器执行链 HandlerExecutionChain中 handle，查找并返回支持handle的 处理器适配器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;
                    }
                }
　　　　　　　　　　//执行所有自定义的拦截器的preHandle（前置处理）方法
                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }

                // Actually invoke the handler.
　　　　　　　　　 // 执行handle返回ModelAndView实例
　　　　　　　　　 // 使用匹配的 HandlerAdapter 处理请求
　　　　　　　　　 // 此处将调用用户自定义的Controller类中的方法
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }

                applyDefaultViewName(processedRequest, mv);
　　　　　　　　　//拦截器后置处理
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
                dispatchException = ex;
            }
            catch (Throwable err) {
                // As of 4.3, we're processing Errors thrown from handler methods as well,
                // making them available for @ExceptionHandler methods and other scenarios.
                dispatchException = new NestedServletException("Handler dispatch failed", err);
            }
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
            triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
        }
        catch (Throwable err) {
            triggerAfterCompletion(processedRequest, response, mappedHandler,
                    new NestedServletException("Handler processing failed", 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);
                }
            }
        }
    }

AbstractHandlerMapping的  getHandler方法，通过HandlerMapping获取处理器执行链：

public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        Object handler = getHandlerInternal(request);//获取hangdle
        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);
        }
　　　　　//添加拦截器
        HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
        if (CorsUtils.isCorsRequest(request)) {
            CorsConfiguration globalConfig = this.globalCorsConfigSource.getCorsConfiguration(request);
            CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
            CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
            executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
        }
        return executionChain;
    }

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

  　　//根据request的url匹配所有拦截器，将拦截器放到处理器执行链中 

　　String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
  for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
   if (interceptor instanceof MappedInterceptor) {
    MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
    if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
     chain.addInterceptor(mappedInterceptor.getInterceptor());
    }
   }
   else {
    chain.addInterceptor(interceptor);
   }
  }
  return chain;
 }