概述
根据web.xml配置我们知道.DispatcherServlet这个类是Spring MVC的关键类。Spring的方法命名很有趣，在Spring进行DI注入的时候,也就是当Application调用getBean方法的时候。getBean方法调用的是doGetBean.而Spring MVC在处理request对象的时候调用的是doService方法。
调用时序图：
通过上面这张时序调用图我们可以看到Dispatcher最终用使用反射调用Method中的invoke方法。而这个方法就是Controller当中的定义的@RequestMapping方法。可以看看之前我的Blog – Spring MVC 之 @RequestMapping。整个从用户request，到服务器response都可以串联起来。下面我们来具体看一看是怎么调用的。
1、doService – Spring MVC处理请求入口
我们来看看处于DispatcherServlet的doService方法。
/**
* Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch}
* for the actual dispatching.
*/
@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
if (logger.isDebugEnabled()) {
String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
" processing " + request.getMethod() + " request for [" + getRequestUri(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<String, Object>();
Enumeration<?> attrNames = request.getAttributeNames();
while (attrNames.hasMoreElements()) {
String attrName = (String) attrNames.nextElement();
if (this.cleanupAfterInclude || attrName.startsWith("org.springframework.web.servlet")) {
attributesSnapshot.put(attrName, request.getAttribute(attrName));
}
}
}
// 1、提供框架对象处理程序和视图对象。(也就是Spring MVC中特殊的几个bean)
request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
// 2、spring mvc支持i18n
request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
// 3、spring mvc支持主题
request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());
// 4、springn mvc支持POST/Redirect/GET模式问题
FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
if (inputFlashMap != null) {
request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
}
request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
try {
// 5、spring mvc分发前端request
doDispatch(request, response);
}
finally {
if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Restore the original attribute snapshot, in case of an include.
if (attributesSnapshot != null) {
restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
}
}这个方法主要的功能实现都在是doDispatch方法中。我们来看一看这个方法。
2、doDispatch – 进行request分发处理的整个流程
下面我们来看看同样处于DispatcherServlet中的doDispatch方法。
/**
* Process the actual dispatching to the handler.
* <p>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.
* <p>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 {
// 步骤1、检查是否是请求是否是multipart（如文件上传）,如果是将通过MultipartResolver解析
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// 步骤2、请求到处理器（页面控制器）的映射，通过HandlerMapping进行映射
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// 步骤3、处理器适配，即将我们的处理器包装成相应的适配器（从而支持多种类型的处理器）
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// 步骤4、如果处理程序支持,处理header中包含last-modified
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;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 步骤5、真正调用适配器执行处理器（这里是调用Controller的入口）
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
// 步骤6、由ViewResolver解析View（viewResolver.resolveViewName(viewName, locale))
applyDefaultViewName(request, mv);
// 步骤7、执行HandlerInterceptor链,并执行post处理
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
// 步骤8、渲染视图(包含对异常的处理)
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Error err) {
triggerAfterCompletionWithError(processedRequest, response, mappedHandler, 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);
}
}
}
}
这样已经拿到了handler这个信息了。其实这个类包装了handler也就是之前文章提到了的HandlerMethod.
3、handle – 调用Controller的入口
这个方法位于org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter#handle()中。
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return handleInternal(request, response, (HandlerMethod) handler);
}其实由上面传过来的handler就是HandlerMethod.就样就合Controller关联了起来。看到这个方法我们下一步就是跟进handleInternal这个方法中去看看。
4、handleInternal – 判断Controller是否使用了@SessionAttributes
这个方法位于org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#handleInternal()中。RequestMappingHandlerAdapter这个类非常重要,我们可以先来看一下它的属性。
Spring MVC不是有支持的方法参数，以及方法返回参数。看到这个类信息，我们就是通过自定义方法参数与自定义方法返回参数来对Spring MVC进行扩展。后面我会用我们项目中的实例来讲解这个功能。这里主要是想给大家打开一个思路。扩展解决问题的方法。
下面我们看看这个方法的具体实现:
@Override
protected final ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
// Always prevent caching in case of session attribute management.
checkAndPrepare(request, response, this.cacheSecondsForSessionAttributeHandlers, true);
}
else {
// Uses configured default cacheSeconds setting.
checkAndPrepare(request, response, true);
}
// Execute invokeHandlerMethod in synchronized block if required.
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
Object mutex = WebUtils.getSessionMutex(session);
synchronized (mutex) {
return invokeHandleMethod(request, response, handlerMethod);
}
}
}
// 1、invoke handlerMethod
return invokeHandleMethod(request, response, handlerMethod);
}调用invoke handlerMethod就是调用Controller具体处理这个请求的方法,我们接着往下看。
5、invokeHandleMethod – 真正分发request处理(异步处理),并创建ModelAndView包装类
这个方法位于org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#invokeHandleMethod()中。
/**
* Invoke the {@link RequestMapping} handler method preparing a {@link ModelAndView}
* if view resolution is required.
*/
private ModelAndView invokeHandleMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
ServletInvocableHandlerMethod requestMappingMethod = createRequestMappingMethod(handlerMethod, binderFactory);
// ModelAndView包装类
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
modelFactory.initModel(webRequest, mavContainer, requestMappingMethod);
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
// DispatcherServlet,就是用于分发请求。而AsyncWebRequest就是异步处理页面请求
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
asyncWebRequest.setTimeout(this.asyncRequestTimeout);
// 异步请求处理器
final WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.setTaskExecutor(this.taskExecutor);
asyncManager.setAsyncWebRequest(asyncWebRequest);
asyncManager.registerCallableInterceptors(this.callableInterceptors);
asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
if (asyncManager.hasConcurrentResult()) {
Object result = asyncManager.getConcurrentResult();
mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
asyncManager.clearConcurrentResult();
if (logger.isDebugEnabled()) {
logger.debug("Found concurrent result value [" + result + "]");
}
requestMappingMethod = requestMappingMethod.wrapConcurrentResult(result);
}
//
requestMappingMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
return getModelAndView(mavContainer, modelFactory, webRequest);
}6、invokeAndHandle – 调用请求处理，并对ModelAndView包装类进行值添加
这个方法位于org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle()
/**
* Invokes the method and handles the return value through a registered
* {@link HandlerMethodReturnValueHandler}.
*
* @param webRequest the current request
* @param mavContainer the ModelAndViewContainer for this request
* @param providedArgs "given" arguments matched by type, not resolved
*/
public final void invokeAndHandle(ServletWebRequest webRequest,
ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {
// 看名字我们就知道这个方法是干什么的了，没错，继续进去。
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
setResponseStatus(webRequest);
if (returnValue == null) {
if (isRequestNotModified(webRequest) || hasResponseStatus() || mavContainer.isRequestHandled()) {
mavContainer.setRequestHandled(true);
return;
}
}
else if (StringUtils.hasText(this.responseReason)) {
mavContainer.setRequestHandled(true);
return;
}
mavContainer.setRequestHandled(false);
try {
this.returnValueHandlers.handleReturnValue(returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
}
catch (Exception ex) {
if (logger.isTraceEnabled()) {
logger.trace(getReturnValueHandlingErrorMessage("Error handling return value", returnValue), ex);
}
throw ex;
}
}7、invokeForRequest – 利用反射调用Contoller处理Request的方法
public final Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
// 1、获取这个方法的请求参数
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
if (logger.isTraceEnabled()) {
StringBuilder sb = new StringBuilder("Invoking [");
sb.append(getBeanType().getSimpleName()).append(".");
sb.append(getMethod().getName()).append("] method with arguments ");
sb.append(Arrays.asList(args));
logger.trace(sb.toString());
}
// 2、利用反射调用Contoller中的方法
Object returnValue = invoke(args);
if (logger.isTraceEnabled()) {
logger.trace("Method [" + getMethod().getName() + "] returned [" + returnValue + "]");
}
return returnValue;
}我们可以看看args的值。
这些值就是Controller对应的请求参数。
那个invoke方法我们就没有必要分析了。以后进入的断点也是进入Controller的指定处理对应的URL的方法中。这样是不是@RequestMapping与Controller之间的关系，也就是页面请求到进入到Controller是不是理清了。后面就是怎么把页面渲染出来的了。这个问题会在以后的blog中分析的。
最后
以上就是糊涂镜子为你收集整理的Spring MVC DispatcherServlet的全部内容，希望文章能够帮你解决Spring MVC DispatcherServlet所遇到的程序开发问题。
如果觉得靠谱客网站的内容还不错，欢迎将靠谱客网站推荐给程序员好友。
本图文内容来源于网友提供，作为学习参考使用，或来自网络收集整理，版权属于原作者所有。
发表评论 取消回复