SpringMVC執(zhí)行流程圖
1.png
在前端控制器中最最重要的方法是 doDispatch,在這個方法中 ,起到委派模式中委派者的角色,負(fù)責(zé)把 任務(wù)分發(fā)給各個角色做處理
分發(fā)的主要任務(wù):
獲取處理器映射器
根據(jù)處理器映射器獲取處理器適配器
根據(jù)處理器適配器獲取視圖ModelAndView
使用視圖解析解解析視圖
渲染視圖
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
//把request對象賦值給 processedRequest
HttpServletRequest processedRequest = request;
//定義 HandlerExecutionChain 如果是訪問controller方法的話,封裝方法對象(方法對象中封裝了controller對象), HandlerExecutionChain還將封裝所有的攔截器
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
//將會通過 ha.handle(processedRequest, response, mappedHandler.getHandler()); 獲取 ModelAndView
ModelAndView mv = null;
Exception dispatchException = null;
try {
// 1.嘗試將當(dāng)前請求轉(zhuǎn)換為MultipartHttpServletRequest
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// 2.查找當(dāng)前請求對應(yīng)的handler，包括Handler（控制器也就是controller本身）本身和Handler攔截器
//當(dāng)遍歷到requestMappingHandlerMapping時 在requestMappingHandlerMapping中其實存儲了 所有攔截器的對象
/**
* 這個方法一路千辛萬苦,一路封裝,滿載而歸
* 1.首先是調(diào)用AbstractHandlerMapping的getHandler方法,然后調(diào)用 AbstractHandlerMethodMapping的getHandlerInternal方法
* 然后重新創(chuàng)建創(chuàng)建對象 new HandlerMethod(this, handler) 把controller對象(從工廠中獲取) 賦值 給方法對象HandlerMethod
* 所以第一步就是: 把controller對象賦值給方法對象
*
* 2.然后調(diào)用AbstractHandlerMapping.getHandlerExecutionChain 轉(zhuǎn)換為 HandlerExecutionChain 對象
* 遍歷攔截器集合 把所有的攔截器對象賦值給HandlerExecutionChain對象
* 所以第二步就是: 把方法對象轉(zhuǎn)換為HandlerExecutionChain對象并把所有的攔截器賦值到其中
*
*/
//根據(jù)請求request對象,調(diào)用處理器映射器尋找處理器,其實就是 HandlerExecutionChain 對象
mappedHandler = getHandler(processedRequest);
/**
* 此時的 mappedHandler 即為 HandlerExecutionChain 對象
* HandlerExecutionChain 對象中 封裝了瀏覽器訪問的方法對應(yīng)的方法對象,方法對象中封裝了對象的controller對象,HandlerExecutionChain封裝了所有的攔截器
*/
// 未能找到對應(yīng)的handler，拋出NoHandlerFoundException異常并返回404
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
// 3.查找當(dāng)前請求對應(yīng)的HandlerAdapter
//把方法對象傳進去,獲取到一個適配器
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
// 4.處理last-modified請求頭，如果當(dāng)前請求支持的話
//獲取方法的請求方法
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;
}
}
// 5.應(yīng)用前置攔截器
// 如果有攔截器返回false，則表明該攔截器已經(jīng)處理了返回結(jié)果，直接返回；
//注意: 此時的 processedRequest 其實就是request 對象
//就是在判斷定義所有的攔截器 的前置方法,返回的到底是true,還是false
//如果有一個前置返回的是false,那么停止執(zhí)行下面的代碼, 只有所有的攔截器的前置方法返回的true才可以
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// Actually invoke the handler.
// 6.調(diào)用HandlerAdapter的handler方法，真正開始處理Controller
//在以上的所有步驟中, ModelAndView都還沒有返回
//這個方法嘗試獲取 ModelAndView 對象 把request對象 ,response對象 和方法對象傳進去
//進入到RequestMappingHandlerAdaper適配器的handleInternal
//準(zhǔn)備獲取ModelAndView對象 同時在方法里面執(zhí)行了controller方法的內(nèi)容
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
//此時ModelAndView對象的view值為跳轉(zhuǎn)的路徑
// 7.如果當(dāng)前請求是并發(fā)處理，直接返回
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
// 8. 如果當(dāng)前返回值中不包含視圖名的話,為返回值設(shè)定默認(rèn)視圖名，
//意思如果你沒有設(shè)置跳轉(zhuǎn)路徑的話,這個方法默認(rèn)給你加跳轉(zhuǎn)路徑
applyDefaultViewName(processedRequest, mv);
// 9.應(yīng)用已注冊攔截器的后置方法。
//倒著遍歷所有的攔截器 先注冊的后執(zhí)行
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
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.
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
// 10.處理分發(fā)調(diào)用結(jié)果,如視圖模型解析、返回等工作 如果以上有任何錯誤,把錯誤信息封裝賦值給dispatchException 錯誤對象
//如果dispatchException不為空的話,打印錯誤信息,如果ModelAndView返回的是一個頁面的話,會重新發(fā)起請求
//如果沒有ModelAndView為空了 ,或者說controller返回不是一個頁面了, 執(zhí)行攔截器的后置方法,也是倒著遍歷
//在這里面還干了一個一件事 ,那就是獲取到了 view視圖對象
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
//整理由多部分請求使用的任何資源。
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
聊一下比較重要的幾個方法
1.獲取處理器映射器
mappedHandler = getHandler(processedRequest);
在doDispatch方法中找這個方法,按住Ctrl鍵點擊進入
此一路千辛萬苦,一路封裝,滿載而歸
@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//handlerMappings中有5個對象
//1. favconHandlerMapping 2.requestMappingHandlerMapping 3.beanNameHandlerMapping 4.resourceHandlerMapping 5.welcomePageHandlerMapping
//遍歷這個五個對象
if (this.handlerMappings != null) {
for (HandlerMapping mapping : this.handlerMappings) {
//當(dāng)遍歷到requestMappingHandlerMapping時 在requestMappingHandlerMapping中其實存儲了 所有攔截器的對象
/**
* 這個方法一路千辛萬苦,一路封裝,滿載而歸
* 1.首先是調(diào)用AbstractHandlerMapping的getHandler方法,然后調(diào)用 AbstractHandlerMethodMapping的getHandlerInternal方法
* 然后重新創(chuàng)建創(chuàng)建對象 new HandlerMethod(this, handler) 把controller對象(從工廠中獲取) 賦值 給方法對象HandlerMethod
* 所以第一步就是: 把controller對象賦值給方法對象
*
* 2.然后調(diào)用AbstractHandlerMapping.getHandlerExecutionChain 轉(zhuǎn)換為 HandlerExecutionChain 對象
* 遍歷攔截器集合 把攔截器所有的對象賦值給HandlerExecutionChain對象的集合
* 所以第二步就是: 把方法對象轉(zhuǎn)換為HandlerExecutionChain對象并把所有的攔截器賦值到其中
*
*/
HandlerExecutionChain handler = mapping.getHandler(request);
if (handler != null) {
return handler;
}
}
}
return null;
}
我們再看一下
mapping.getHandler(request);方法
按住Ctrl鍵點擊進入,發(fā)現(xiàn)是HandlerMapping接口 , 按住快捷鍵 Ctrl + Alt + B 選擇AbstractHandlerMapping 這個實現(xiàn)類
@Override
@Nullable
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//獲取Controller對象,但是獲取到時對應(yīng)方法的對象,方法對象中封裝有controller對象
//一路獲取controller對象,把controller對象封裝進方法對象中,(前提是訪問的是controller中的方法)
Object handler = getHandlerInternal(request);
if (handler == null) {
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = obtainApplicationContext().getBean(handlerName);
}
//把方法對象和request傳進去 ,準(zhǔn)備把所有的攔截器封裝進 HandlerExecutionChain對象中
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
// 現(xiàn)在 HandlerExecutionChain 對象中有 方法對象 而方法對象中存儲了controller對象, HandlerExecutionChain中有所有的攔截器對象
if (logger.isTraceEnabled()) {
logger.trace("Mapped to " + handler);
}
else if (logger.isDebugEnabled() && !request.getDispatcherType().equals(DispatcherType.ASYNC)) {
logger.debug("Mapped to " + executionChain.getHandler());
}
if (CorsUtils.isCorsRequest(request)) {
CorsConfiguration globalConfig = this.corsConfigurationSource.getCorsConfiguration(request);
CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}
2.獲取處理器適配器
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
我們再回到 doDispatch方法中,找到該方法, 按住Ctrl鍵點擊進入
//參數(shù)為對應(yīng)方法對象,或者是頁面資源對象
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
//handlerAdapters 有三個適配器對象
//1.RquestMappingHandlerAdapter 2.HttpRequestHandlerAdapter 3.SimpleControllerHandlerAdapter
if (this.handlerAdapters != null) {
for (HandlerAdapter adapter : this.handlerAdapters) {
//查看哪個處理器符合請求需要的,返回符合條件的處理器
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");
}
3.獲取視圖ModelAndView
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
我們再回到 doDispatch方法中,找到該方法, 點擊進入
發(fā)現(xiàn)是一個HandlerAdapter接口 ,按住快捷鍵 Ctrl + Alt + B ,選擇 AbstractHandlerMethodAdaper
按住Ctrl鍵點擊 handleInternal 方法,發(fā)現(xiàn)是一個抽象的方法,再次 按住快捷鍵 Ctrl + Alt + B 進入到RequestMappingHandlerAdapter
@Override
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
checkRequest(request);
//如果需要，在同步塊中執(zhí)行InvokehandlerMethod。
// 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) {
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No HttpSession available -> no mutex necessary
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No synchronization on session demanded at all...
//嘗試獲取ModelAndView對象,如果沒有HTML,則獲取不到視圖
//這個方法里面執(zhí)行了controller的內(nèi)容
mav = invokeHandlerMethod(request, response, handlerMethod);
}
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}
}
//獲取到ModelAndView對象
return mav;
}
4.解析視圖
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
我們再回到 doDispatch方法中,找到該方法, 按住Ctrl鍵點擊進入
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) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
//處理程序是否返回要呈現(xiàn)的視圖？
// Did the handler return a view to render?
if (mv != null && !mv.wasCleared()) {
//這個方法當(dāng)中會獲取到視圖view
render(mv, request, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("No view rendering, null ModelAndView returned.");
}
}
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Concurrent handling started during a forward
return;
}
if (mappedHandler != null) {
//如果沒有ModelAndView為空了 ,或者說controller返回不是一個頁面了,執(zhí)行攔截器的后置方法,也是倒著遍歷
mappedHandler.triggerAfterCompletion(request, response, null);
}
}
找到 render(mv, request, response); 方法, 按住Ctrl鍵點擊進入
protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
// Determine locale for request and apply it to the response.
Locale locale =
(this.localeResolver != null ? this.localeResolver.resolveLocale(request) : request.getLocale());
response.setLocale(locale);
View view;
String viewName = mv.getViewName();
if (viewName != null) {
//我們需要解析視圖名稱
// We need to resolve the view name.
//獲取到了視圖
view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
if (view == null) {
throw new ServletException("Could not resolve view with name '" + mv.getViewName() +
"' in servlet with name '" + getServletName() + "'");
}
}
else {
// No need to lookup: the ModelAndView object contains the actual View object.
view = mv.getView();
if (view == null) {
throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
"View object in servlet with name '" + getServletName() + "'");
}
}
// Delegate to the View object for rendering.
if (logger.isTraceEnabled()) {
logger.trace("Rendering view [" + view + "] ");
}
try {
if (mv.getStatus() != null) {
response.setStatus(mv.getStatus().value());
}
//獲取到視圖之后
view.render(mv.getModelInternal(), request, response);
}
catch (Exception ex) {
if (logger.isDebugEnabled()) {
logger.debug("Error rendering view [" + view + "]", ex);
}
throw ex;
}
}
這個方法中,解析視圖ModelAndView ,獲取View對象
