上一篇总结了SpringMvc的前端控制器DispatcherServlet整体的初始话过程，最终分析到DispatcherServlet.doDispatch()方法，本篇就是主要分析SpringMvc的核心，doDispatch()方法处理请求的整体流程。
doDispatch方法整体源码：
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
//HandlerExecutionChain（处理器执行链）保存需要执行的处理器和拦截器
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
//异步请求管理器
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
//检查是否为Multipart请求，如果是则返回的是一个MultipartHttpServletRequest类型的request，不是则返回原来的request
processedRequest = checkMultipart(request);
//根据返回是否原来的对象来判断，request是否已经被处理过
multipartRequestParsed = (processedRequest != request);
//根据uri找到HandlerExecutionChain（包含了我们写的处理器和拦截器）
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
//获取到处理器适配器，用于执行HandlerExecutionChain
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
//处理last-modified缓存机制，处理器支持需要实现LastModified接口
String method = request.getMethod();
boolean isGet = "GET".equals(method);
//last-modified 只支持get或者HEAD请求
if (isGet || "HEAD".equals(method)) {
//上次修改资源的时间
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {
logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
//修改时间与上次请求的时间一致，那么表示资源未改变，直接返回304状态码，浏览器使用上次缓存结果
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
//执行mappedHandler中所有HandlerInterceptor（拦截器）applyPreHandle方法
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
//如果有applyPreHandle返回的是false,则结束doDispatch方法的执行
return;
}
// 执行处理器方法，返回ModelAndView
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
//如果本次是异步请求，直接退出doDispatch方法的执行
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
//如果返回的ModelAndView中的ViewName为空时，设置一个默认的ViewName
applyDefaultViewName(processedRequest, mv);
//执行mappedHandler中所有HandlerInterceptor（拦截器）applyPostHandle方法
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
//保存异常，用于后面的@ExceptionHandler方法处理
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.
//保存错误，用于后面的@ExceptionHandler方法处理
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
//处理结果并响应浏览器
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
//异常时，也会执行mappedHandler中所有HandlerInterceptor（拦截器）AfterCompletion方法
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
//错误时，也会执行mappedHandler中所有HandlerInterceptor（拦截器）AfterCompletion方法
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
//如果是异步请求，执行mappedHandler中所有AsyncHandlerInterceptor（异步拦截器）的afterConcurrentHandlingStarted方法
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// 关闭Multipart请求的相关资源
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
接下来具体分析几个重要步骤：
[TOC]
1）getHandler(processedRequest)：找到需要执行的处理器执行链（HandlerExecutionChain）
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//遍历每一个HandlerMapping执行getHandler方法，直到获取到一个HandlerExecutionChain，并返回
for (HandlerMapping hm : this.handlerMappings) {
if (logger.isTraceEnabled()) {
logger.trace(
"Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
}
HandlerExecutionChain handler = hm.getHandler(request);
if (handler != null) {
return handler;
}
}
return null;
}
DispatcherServlet.properties中默认配置的HandlerMapping：
org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping：根据Controller在ioc容器中的name或者alias（别名）查找
org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping（已过时）
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter（代替DefaultAnnotationHandlerMapping: 用于查找标注了@RequestMapping等注解的处理器，最常用
2）getHandlerAdapter(mappedHandler.getHandler())找到支持的对应处理器的处理器适配器一般现在都是用RequestMappingHandlerAdapter：
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
//遍历所有的HandlerAdapter，执行supports来找到支持的对应处理器的处理器适配器
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");
}
DispatcherServlet.properties中默认配置的HandlerAdapter：
org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter：用来执行实现了RequestHandler接口的Controller
org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter：用来执行实现了Controller接口的Controller
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter（已过时）
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping（代替AnnotationMethodHandlerAdapter）：执行标注了@RequestMapping等注解的处理器，最常用
3）mappedHandler.applyPreHandle(processedRequest, response)执行HandlerExecutionChain中所有拦截器的applyPreHandle(processedRequest, response)方法
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
//遍历执行Interceptor.preHandle
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = 0; i < interceptors.length; i++) {
HandlerInterceptor interceptor = interceptors[i];
//preHandle(request, response, this.handler)返回false,则triggerAfterCompletion(request, response, null)，并不再执行接下来的其他处理器的preHandle
if (!interceptor.preHandle(request, response, this.handler)) {
triggerAfterCompletion(request, response, null);
return false;
}
//保存最后一个preHandle(request, response, this.handler)返回true的拦截器索引值
this.interceptorIndex = i;
}
}
return true;
}
4）triggerAfterCompletion(request, response, null)：如果存在拦截器的applyPreHandle方法返回false,则触发执行拦截器的afterCompletion方法：
void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
//逆序执行上一步preHandle(request, response, this.handler)返回true的拦截器的afterCompletion方法
for (int i = this.interceptorIndex; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
try {
interceptor.afterCompletion(request, response, this.handler, ex);
}
catch (Throwable ex2) {
logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
}
}
}
}
5）ha.handle(processedRequest, response, mappedHandler.getHandler())使用处理器适配器执行处理器方法：
@Override//handlerMethod保存了处理器对象和当前需要执行的处理器方法等信息
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
checkRequest(request);
// this.synchronizeOnSession 默认为false,对于同一个session的request,是否同步执行处理器方法.
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
Object mutex = WebUtils.getSessionMutex(session);
synchronized (mutex) {
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No HttpSession available -> no mutex necessary
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
//执行处理器方法
mav = invokeHandlerMethod(request, response, handlerMethod);
}
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}
}
return mav;
}
直接看invokeHandlerMethod(request, response, handler)：
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
//查找处理器中标注了@InitBinder的方法及相应的@ControllerAdvice类，保存在binderFactory
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
//查找处理器中标注了@ModelAttribute的方法及相应的@ControllerAdvice类，保存在modelFactory中
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
//ServletInvocableHandlerMethod：可执行的处理器方法
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
//设置处理器方法参数解析器
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
//处理器方法返回值的处理器
invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers)；
invocableMethod.setDataBinderFactory(binderFactory);
//参数名称发现器
invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
//mavContainer用于存放所有可能会用到的ModelAndView
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
//添加重定向参数
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
//初始化model,就是填充model,添加Sesson中的参数名与处理器方法参数一致的参数，执行@ModelAttribute标注的处理器方法
modelFactory.initModel(webRequest, mavContainer, invocableMethod);
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
//下面是异步请求相关
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response); //设置异步执行，超时时间
asyncWebRequest.setTimeout(this.asyncRequestTimeout);
//异步管理器
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
//设置异步执行器
asyncManager.setTaskExecutor(this.taskExecutor);
//设置异步请求
asyncManager.setAsyncWebRequest(asyncWebRequest);
//注册返回值为Callable的异步拦截器
asyncManager.registerCallableInterceptors(this.callableInterceptors);
//注册返回值为DeferredResult的异步拦截器
asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
//如果本次请求时异步请求的转发
if (asyncManager.hasConcurrentResult()) {
Object result = asyncManager.getConcurrentResult();
mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
asyncManager.clearConcurrentResult();
if (logger.isDebugEnabled()) {
logger.debug("Found concurrent result value [" + result + "]");
}
invocableMethod = invocableMethod.wrapConcurrentResult(result);
}
//执行处理器：大概步骤：解析处理器方法参数 反射调用处理器方法 解析返回值等操作
invocableMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
//返回ModelAndView对象
return getModelAndView(mavContainer, modelFactory, webRequest);
}
finally {
webRequest.requestCompleted();
}
}
6）mappedHandler.applyPostHandle(processedRequest, response, mv):执行拦截器的postHandle方法
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
//逆序执行
for (int i = interceptors.length - 1; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
interceptor.postHandle(request, response, this.handler, mv);
}
}
}
7）processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException)：处理结果并响应给浏览器
//exception 执行处理器方法报错时被捕获的异常
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {
boolean errorView = false;
//如果存在异常
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
//处理异常，执行自定义异常处理方法即被@ExceptionHandler标注，并返回一个ModelAndView
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
//如果mv不为空，且没有被清理，也就是请求在此之前还没有响应浏览器
if (mv != null && !mv.wasCleared()) {
//使用视图解析器获取视图对象，渲染视图，响应浏览器
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) {
//执行所有拦截器的AfterCompletion方法
mappedHandler.triggerAfterCompletion(request, response, null);
}
}
结束。。。