这是一个最经典的SpringMVC执行流程图，其中最核心的三个地方是： HandlerMapping、HandlerAdapter、HttpMessageConverter。
首先，从DispatcherServlet入手，先看下DispatcherServlet继承图：
从图可以得知，DispatcherServlet本质上就是Servlet，那么Servlet生命周期最主要的的三个方法时：void init(ServletConfig config)，void service(ServletRequest request,ServletResponse response)，void destroy()。
看了源代码之后发现DispatcherServlet里面根本没有service这个方法，这个时候找到它的父类FrameworkServlet ，
doDispatch,最主要的方法，用来分发请求，核心的逻辑都在这里面（截图有限，自己看源码吧）
主要的：
1.checkMultipart方法检查是否是二进制的请求(文件上传的请求)
2.mappingHandler=getHandler(request)
返回的是HandlerExecutionChain(处理执行链)
再看DispatcherServlet.properties其实就是包装了不同的Mapping来判断通过何种方式来配置。
HandlerExecutionChain(处理执行链)包含两部分内容,一部分是请求对应的控制器,一部分是拦截器,真正执行handle之前,有一系列操作,例如数据转换,格式化,数据验证这些,都是由拦截器来做的
另外需要注意的是,假如你自定义了n个拦截器,会发现HandlerExecutionChain会有n+1个拦截器,说明有一个是他内部有的,从这里我们可以知道它的执行顺序,比如这里要先执行拦截器,再执行我们控制器,所以这个东西被称为处理执行链
3.ha = getHandlerAdapter(mappedHandler.getHandler());
![Uploading applyPreHandler_524696.png . . .]
HandlerAdapater(处理器适配器)，用来执行handler(控制器，即contorller)
这里判断handler适不适合这个RequestMappingAdapter，适合就返回
if(ha.supports(handler))
return ha;
获取方法类型
String method = reqyest,getMethod();
if(!mappedHandler.applyPreHandle(processedRequest, response)){
return;
}
这里主要遍历拦截器。
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
这里去调用handler方法，这个方法会做很多事情，比如参数自动装入。
然后是
@RequestMapping(value = "/golist.do")
public ModelAndView golist(HttpServletRequest request) {
return new ModelAndView("/views/module/advise/list.jsp");
}
再继续
//默认视图名称
applyDefaultViewName(request, mv);
像下面这个 返回的只有model 没有 view
@RequestMapping(value = "/saveEntity.do")
public @ResponseBody AjaxResult saveByEntity(HttpServletRequest request, Advise entity) {
LoginUser loginUser = LoginUserUtil.getCurrentUser(request);
adviseService.saveEntity(loginUser, entity);
return AjaxResult.warpAjaxResult(true);
}
继续往下
mappedHandler.applyPostHandle(processedRequest, response, mv);
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv)
throws Exception
{
if(getInterceptors() == null)
return;
for(int i = getInterceptors().length - 1; i >= 0; i--)
{
HandlerInterceptor interceptor = getInterceptors()[i];
interceptor.postHandle(request, response, handler, mv);
}
}
从这里我们知道，Interceptor的执行顺序是反过来的：如图
再继续
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
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 ? null : mappedHandler.getHandler();
mv = processHandlerException(request, response, handler, exception);
errorView = mv != null;
}
if(mv != null && !mv.wasCleared())
{
render(mv, request, response);
if(errorView)
WebUtils.clearErrorRequestAttributes(request);
} else
if(logger.isDebugEnabled())
logger.debug((new StringBuilder()).append("Null ModelAndView returned to DispatcherServlet with name '").append(getServletName()).append("': assuming HandlerAdapter completed request handling").toString());
if(WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted())
return;
if(mappedHandler != null)
mappedHandler.triggerAfterCompletion(request, response, null);
}
protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response)
throws Exception
{
Locale locale = localeResolver.resolveLocale(request);
response.setLocale(locale);
View view;
if(mv.isReference())
{
view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);
if(view == null)
throw new ServletException((new StringBuilder()).append("Could not resolve view with name '").append(mv.getViewName()).append("' in servlet with name '").append(getServletName()).append("'").toString());
} else
{
view = mv.getView();
if(view == null)
throw new ServletException((new StringBuilder()).append("ModelAndView [").append(mv).append("] neither contains a view name nor a ").append("View object in servlet with name '").append(getServletName()).append("'").toString());
}
if(logger.isDebugEnabled())
logger.debug((new StringBuilder()).append("Rendering view [").append(view).append("] in DispatcherServlet with name '").append(getServletName()).append("'").toString());
try
{
//这里决定究竟是转发还是重定向,或者说变成其他视图
view.render(mv.getModelInternal(), request, response);
}
catch(Exception ex)
{
if(logger.isDebugEnabled())
logger.debug((new StringBuilder()).append("Error rendering view [").append(view).append("] in DispatcherServlet with name '").append(getServletName()).append("'").toString(), ex);
throw ex;
}
}
public void render(Map model, HttpServletRequest request, HttpServletResponse response)
throws Exception
{
if(logger.isTraceEnabled())
logger.trace((new StringBuilder()).append("Rendering view with name '").append(beanName).append("' with model ").append(model).append(" and static attributes ").append(staticAttributes).toString());
Map mergedModel = createMergedOutputModel(model, request, response);
prepareResponse(request, response);
renderMergedOutputModel(mergedModel, request, response);
}