调用doDispatch()方法处理流程梳理：
1、getHandler()：根据当前请求在HandlerMapping中找到这个请求的映射信息，获取到目标处理器类。
2、getHandlerAdapter()：根据当前处理器类，找到当前类的HandlerAdapter适配器。
3、使用刚才获取到的适配器利用反射执行目标方法。
4、目标方法执行后会返回一个ModelAndView对象。
5、根据ModelAndView的信息转发到具体的页面。
一、前端控制器DispatcherServlet部分
1、doDispatch()：
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
try {
ModelAndView mv = null;
Object dispatchException = null;
try {
processedRequest = this.checkMultipart(request); //检查是否文件上传请求
multipartRequestParsed = processedRequest != request;
mappedHandler = this.getHandler(processedRequest); //根据请求的URL找到由哪一个控制器去处理
if (mappedHandler == null) {
this.noHandlerFound(processedRequest, response);
return;
}
HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler()); //拿到对应控制器的适配器
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if ((new ServletWebRequest(request, response)).checkNotModified(lastModified) && isGet) {
return;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); //适配器将执行后的信息封装成ModelAndView
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
this.applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
} catch (Exception var20) {
dispatchException = var20;
} catch (Throwable var21) {
dispatchException = new NestedServletException("Handler dispatch failed", var21);
}
this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException); //转发到对应页面
} catch (Exception var22) {
this.triggerAfterCompletion(processedRequest, response, mappedHandler, var22);
} catch (Throwable var23) {
this.triggerAfterCompletion(processedRequest, response, mappedHandler, new NestedServletException("Handler processing failed", var23));
}
} finally {
if (asyncManager.isConcurrentHandlingStarted()) {
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
} else if (multipartRequestParsed) {
this.cleanupMultipart(processedRequest);
}
}
}
2、getHandler(processedRequest)：
得到请求与控制器的映射关系。
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
if (this.handlerMappings != null) {
Iterator var2 = this.handlerMappings.iterator();
while(var2.hasNext()) {
HandlerMapping mapping = (HandlerMapping)var2.next();
HandlerExecutionChain handler = mapping.getHandler(request); //递归查找
if (handler != null) {
return handler; //说明前端传过来的URL和注解上的路径匹配, 就返回对应的控制器
}
}
}
return null;
}
HandlerMapping(九大组件初始化的时候就有值了)中存放的Object：
3、getHandlerAdapter(mappedHandler.getHandler())：
得到请求与目标方法的映射关系。
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
if (this.handlerAdapters != null) {
Iterator var2 = this.handlerAdapters.iterator();
while(var2.hasNext()) {
HandlerAdapter adapter = (HandlerAdapter)var2.next();
if (adapter.supports(handler)) {
return adapter;
}
}
}
throw new ServletException("No adapter for handler [" + handler + "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}
适配器的类型：
4、ha.handle(processedRequest, response, mappedHandler.getHandler())：
确定方法运行时的参数，利用反射执行目标方法。
Spring4.0参数确定机制，5.0不太清楚到底是不是这样的，Debug源码太难了，我是个菜鸡啊啊。。。来自尚硅谷LFY大神：
小结：先根据请求得地址找到对应的控制器类，再找到目标方法的适配器，确定参数并利用反射调用目标方法。
二、视图解析部分
1、processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException)：
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response, @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv, @Nullable Exception exception) throws Exception {
boolean errorView = false;
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
this.logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException)exception).getModelAndView();
} else {
Object handler = mappedHandler != null ? mappedHandler.getHandler() : null;
mv = this.processHandlerException(request, response, handler, exception);
errorView = mv != null;
}
}
if (mv != null && !mv.wasCleared()) {
this.render(mv, request, response); //渲染页面
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
} else if (this.logger.isTraceEnabled()) {
this.logger.trace("No view rendering, null ModelAndView returned.");
}
if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
if (mappedHandler != null) {
mappedHandler.triggerAfterCompletion(request, response, (Exception)null);
}
}
}
2、render(mv, request, response)：
protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
Locale locale = this.localeResolver != null ? this.localeResolver.resolveLocale(request) : request.getLocale();
response.setLocale(locale);
String viewName = mv.getViewName();
View view;
if (viewName != null) {
view = this.resolveViewName(viewName, mv.getModelInternal(), locale, request); //根据viewName解析得到view
if (view == null) {
throw new ServletException("Could not resolve view with name '" + mv.getViewName() + "' in servlet with name '" + this.getServletName() + "'");
}
} else {
view = mv.getView();
if (view == null) {
throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a View object in servlet with name '" + this.getServletName() + "'");
}
}
if (this.logger.isTraceEnabled()) {
this.logger.trace("Rendering view [" + view + "] ");
}
try {
if (mv.getStatus() != null) {
response.setStatus(mv.getStatus().value());
}
view.render(mv.getModelInternal(), request, response); //调用View的函数去渲染
} catch (Exception var8) {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Error rendering view [" + view + "]", var8);
}
throw var8;
}
}
3、resolveViewName(viewName, mv.getModelInternal(), locale, request)：
protected View resolveViewName(String viewName, @Nullable Map<String, Object> model, Locale locale, HttpServletRequest request) throws Exception {
if (this.viewResolvers != null) {
Iterator var5 = this.viewResolvers.iterator();
while(var5.hasNext()) {
ViewResolver viewResolver = (ViewResolver)var5.next();
View view = viewResolver.resolveViewName(viewName, locale); //得到view, 这个东西其实是九大组件之一
if (view != null) {
return view;
}
}
}
return null;
}
当视图解析器为空的时候，Spring4.0会用默认的InternalResourceViewResolver视图解析器。
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SpringMVC有不同的视图解析器，4.0版本当返回的viewName中带有redirect或forward前缀的时候，会新建对应的视图对象。非这两个前缀的话都会带上国际化信息并用InternalResourceViewResolver拼接URL。
4、view.render(mv.getModelInternal(), request, response)：
运行时确定是哪个View，将数据保存到隐含模型中。
SpringMVC4.0隐含模型保存参数的确定机制，5.0不太清楚到底是不是这样的，来自尚硅谷LFY大神：
小结：视图解析器只是为了得到视图对象；视图对象才能真正的转发或者重定向到页面并渲染视图。
总结：学到现在，个人感觉SpringMVC牛逼的一个地方在于隐含模型，每次请求都会在request域中放值到隐含模型中，真的太强了。
