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千鋒扣丁學(xué)堂Java培訓(xùn)之帶你從代碼看spring mvc請求處理過程

2019-06-25 13:50:57 1160瀏覽

今天千鋒扣丁學(xué)堂Java培訓(xùn)老師給大家分享一篇關(guān)于從源碼角度看spring mvc的請求處理過程，文中通過示例代碼介紹的非常詳細(xì)，對大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價值，下面我們一起來看一下吧。

請求處理的過程：

1.DispatcherServelt作為前端控制器，攔截request對象。

2.DispatcherServlet接收到request對象之后，查詢HandlerMapping,得到一個HandlerExecutionChain對象。

3.DispatcherServlet將Handler對象交由HandlerAdapter(適配器模式的典型應(yīng)用)，調(diào)用相應(yīng)的controller方法。

4.Controller方法返回ModelAndView對象，DispatcherServlet將view交由ViewResolver進(jìn)行解析，得到相應(yīng)的視圖。用model渲染視圖。

5.返回響應(yīng)結(jié)果。

整個過程的流程其實就是DispatcherServelt中doDispatch()方法的調(diào)用過程。

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
//第一步攔截request對象，doDispatch()方法在doService()方法中被調(diào)用，request對象是經(jīng)過處理的。
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
//和文件的上傳和下載有關(guān)系，判斷請求的類型是否是multipart類型
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
//主要看這里，這里是得到HandlerExecutionChain的方法。關(guān)于Handler()方法向下看
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
//這里已經(jīng)獲取到HandlerExecutionChain對象，接下來就要獲取HandlerAdapter對象，調(diào)用Handler對象的方法。
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler
//有關(guān)瀏覽器緩存的設(shè)定（304）
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;
}
}
//pan'du
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
//解析視圖，數(shù)據(jù)渲染
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
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//遍歷HandlerMappingList對象（存儲若干個HandlerMapping對象），不斷調(diào)用，直到不為空為止，否則返回null
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;
}

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