关于SpringMvc的DispatcherServlet的工作流程的理解与梳理

          首先，我们看一下DispatcherServlet的继承关系图。这里，我们着重看一下Servlet部分的继承树。下图中我们可以看到，DispatcherServlet就是实现了Servlet接口。而用来处理请求的service方法在其父类FrameworkServlet中进行了重写。

     其次，咱们看一下doService方法：在此方法中，除了定义了请求的属性及对应的操作外，主要是调用了doDispatch方法来处理请求的。

@Override
	protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
		logRequest(request);

		// 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<>();
			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.