接上一篇：Spring MVC源碼解析二
- spring mvc請求分發(fā)鏈路：
通過時序圖可以看到，servlet對request請求進行攔截后，先后調(diào)用了FrameworkServlet的processRequest()热某、doService()，最終調(diào)用了DispatcherServlet的doDispatch()方法
doDispatch的源碼：
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);
// Determine handler for the current request.
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// 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;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
try {
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
}
applyDefaultViewName(request, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
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
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
return;
}
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
核心處理如下：
mappedHandler = getHandler() //get handler by url handlermapping
ha = getHandlerAdapter() //get handleradapter
ha.handle() //通過adapter調(diào)用handler的處理方法
processDispatchResult() //處理doDispatch的處理結(jié)果
分別查看源碼：
getHandler()
/**
* Return the HandlerExecutionChain for this request.
* <p>Tries all handler mappings in order.
* @param request current HTTP request
* @return the HandlerExecutionChain, or {@code null} if no handler could be found
*/
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
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;
}
1唐全、getHandler()主要就是通過this.handlerMappings中的HandlerMapping實例來對具體request映射一個handler（spring mvc中的controller類和controller類中的具體方法） 2哨啃、如果看過[spring mvc源碼解析二]中對于this.handlerMappings初始化的解讀，便知道HandlerMapping的具體實現(xiàn)有3個： 1.RequestMappingHandlerMapping 2.BeanNameUrlHandlerMapping 3.SimpleUrlHandlerMapping 3斟珊、spring mvc中正是通過這3個類實現(xiàn)了重要的request和controller的mapping
getHandlerAdapter從this.handlerAdapters中匹配獲取對應的handlerAdapter苇倡，且獲取對應的handler
/**
* Return the HandlerAdapter for this handler object.
* @param handler the handler object to find an adapter for
* @throws ServletException if no HandlerAdapter can be found for the handler. This is a fatal error.
*/
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
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");
}
handle()是HandleAdapter中定義的接口，具體的實現(xiàn)類有很多囤踩，在DispatcherServlet中具體使用哪個實現(xiàn)旨椒，是由上一步調(diào)用的getHandlerAdapter決定的，handle()接口的具體作用如接口注釋描述：使用指定的handler來處理http請求
/**
* Use the given handler to handle this request.
* The workflow that is required may vary widely.
* @param request current HTTP request
* @param response current HTTP response
* @param handler handler to use. This object must have previously been passed
* to the {@code supports} method of this interface, which must have
* returned {@code true}.
* @throws Exception in case of errors
* @return ModelAndView object with the name of the view and the required
* model data, or {@code null} if the request has been handled directly
*/
ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;
