SpringMVC核心处理流程：
1、DispatcherServlet前端控制器接收发过来的请求，交给HandlerMapping处理器映射器
2、HandlerMapping处理器映射器，根据请求路径找到相应的HandlerAdapter处理器适配器（处理器适配器就是那些拦截器或Controller）
3、HandlerAdapter处理器适配器，请求数据绑定和转换，处理一些功能请求，返回一个ModelAndView对象（包括模型数据、逻辑视图名）
4、ViewResolver视图解析器，先根据ModelAndView中设置的View解析具体视图
5、然后再将Model模型中的数据渲染到View上
这些过程都是以DispatcherServlet为中轴线进行的。
1.入口源码
springMVC的请求会交由dispatcherServlet处理，其本质上是一个多线程的请求处理机制；核心业务逻辑被设计在doDispatcher(..)方法中；
/**
* Process the actual dispatching to the handler.
* 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.
*
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);
// 绑定url -> 具体的handler/Controller.method(..)
// Determine handler for the current request.
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// 根据handler绑定具体的adapter
// Determine handler adapter for the current request.
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;
}
}
// interceptor 拦截器进行前置预处理
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 在handle方法中进行了请求数据的绑定，方法invoke，返回model的处理和封装等
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
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);
}
}
}
}
2.核心关注的几个问题
2.1 请求如何路由到具体的Controller上的方法进行处理?
根据请求路径，与已知的handlerMapping进行匹配，并加入interceptors:
dispatcherServlet.getHandler()最终调用AbstracteHandlerMapping.getHandlerExecutionChain(..)中
进行url与handlerMapping进行匹配，并加入interceptors;
2.2 扁平化的前端请求数据如何进行数据绑定？
我们知道，前端的get/post等请求，会被requestServlet接受，并封装成HttpServletRequest的parameterMap中，每一项请求的数据结构都是 K-V 形的。
而我们知道，像这样的形式，那么在这个中间数据如何实现数据绑定到Bean，String格式的Value 转换成各种目标格式。
事实上，spring MVC将整个网络请求的处理流程进行了合理的切分,其大致的处理流程如下：
1.调用匹配到的adapter.handle(..)
2.然后调用invokeAndHandle(..)
3.调用invokeForRequest(..)获取getMethodArgumentValues(..)获取和绑定入参;
4.在具体的方法中，获取支持处理的argumentResolvers,然后调用resolveArgument(..)方法;
5.在ModelAttributeMethodProcessor中调用bindRequestParameters(binder, webRequest),方法，然后再调用bind()进行bean参数的绑定；
6.调用binder.convertIfNecessary(arg, parameter.getParameterType(), parameter)方法进行参数的转换；