1、前言

總是總結一些皮毛的知識點，今天來學習點高大尚的東西，根據原始碼簡單分析springmvc的啟動過程。

2、springmvc的架構流程圖

3、原始碼分析

       /**
	 * 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 {
                /*
                    1、springmvc容器初始化的完成後，handermapping就已經被載入了，這些handermappings被放在一個List集合中。該List集合中儲存了
                    HTTP請求對應的對映資料。
                */
                HttpServletRequest processedRequest = request;
                
                //攔截器鏈
                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.
                                /*
                                    2、通過HanderMapping介面中getHander（）方法，獲取hander執行鏈。
                                    獲取的執行鏈中包含需要的hander以及interceptors（攔截器鏈）
                                */
                                mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null || mappedHandler.getHandler() == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

				// Determine handler adapter for the current request.
                                /*
                                    通過hander執行鏈獲取HanderAdapter    
                                */
                                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				// Process last-modified header, if supported by the handler.
                                /*
                                    3、通過獲取到的HanderAdapter，校驗（適配）hander的合法性                               
                                */
                                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.
                                /*
                                    校驗合法後，會返回ModelAndView：資料模型和檢視名稱
                                */
                                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				if (asyncManager.isConcurrentHandlingStarted()) {
					return;
				}
                                /*
                                    4、渲染檢視
                                */
				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);
				}
			}
		}
	}
 

4、解釋專案啟動HanderMapping被載入

通過專案啟動的日誌，可以看出載入過程,如圖：

5、解釋HandlerExecutionChain中包含攔截器

直接看原始碼：

public class HandlerExecutionChain {

	private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);

	private final Object handler;
        //攔截器陣列
	private HandlerInterceptor[] interceptors;

	private List<HandlerInterceptor> interceptorList;

	private int interceptorIndex = -1;
        
        //...
}
 

6、解釋通過介面卡如何校驗Hander的合法性的原始碼

protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
	for (HandlerAdapter ha : this.handlerAdapters) {
		if (logger.isTraceEnabled()) {
			logger.trace("Testing handler adapter [" + ha + "]");
		}
		if (ha.supports(handler)) {
			return ha;
		}
	}
	throw new ServletException("No adapter for handler [" + handler +
		"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}
 

7、解釋渲染檢視的原始碼

/**
	 * Do we need view name translation?
	 */
	private void applyDefaultViewName(HttpServletRequest request, ModelAndView mv) throws Exception {
		if (mv != null && !mv.hasView()) {
			mv.setViewName(getDefaultViewName(request));
		}
	}

	/**
	 * Handle the result of handler selection and handler invocation, which is
	 * either a ModelAndView or an Exception to be resolved to a ModelAndView.
	 */
	private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {

		boolean errorView = false;

		if (exception != null) {
			if (exception instanceof ModelAndViewDefiningException) {
				logger.debug("ModelAndViewDefiningException encountered", exception);
				mv = ((ModelAndViewDefiningException) exception).getModelAndView();
			}
			else {
				Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
				mv = processHandlerException(request, response, handler, exception);
				errorView = (mv != null);
			}
		}

		// Did the handler return a view to render?
		if (mv != null && !mv.wasCleared()) {
			render(mv, request, response);
			if (errorView) {
				WebUtils.clearErrorRequestAttributes(request);
			}
		}
		else {
			if (logger.isDebugEnabled()) {
				logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
						"': assuming HandlerAdapter completed request handling");
			}
		}

		if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
			// Concurrent handling started during a forward
			return;
		}

		if (mappedHandler != null) {
			mappedHandler.triggerAfterCompletion(request, response, null);
		}
	}

8、結束

通過上述一系列的操作，使用者通過請求就可以看到想要的檢視效果了。