MVC 處理 HTTP 分發請求
HandlerMapping 配置與設計
在初始化完成時,在上下文環境中已定義的所有 HandlerMapping 都已經被加載了,這些加載的 handlerMapping 被放在一個 List 中並被排序,存儲着 HTTP 請求對應的映射數據。這個 List 中的每一個元素都對應着一個具體 handlerMapping 的配置,一般每一個 handlerMapping 可以持有一系列從 URL 請求到 Controller 的映射,而 Spring MVC 提供了一系列的 HandlerMapping 實現。如下:
通過這些在 HandlerMapping 中定義的映射關係,即這些 URL 請求和控制器的對應關係,使 Spring MVC 應用可以根據 HTTP 請求確定一個對應的 Controller。具體來說,這些映射關係是通過接口類 HandlerMapping 來封裝的,在 HandlerMapping 接口中定義了一個 getHandler 方法,通過這個方法,可以獲得與 HTTP 請求對應的 HandlerExecutionChain,而這個 HandlerExecutionChain,封裝了具體的 Controller 對象:
public interface HandlerMapping {
String PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE = HandlerMapping.class.getName() + ".pathWithinHandlerMapping";
String BEST_MATCHING_PATTERN_ATTRIBUTE = HandlerMapping.class.getName() + ".bestMatchingPattern";
String INTROSPECT_TYPE_LEVEL_MAPPING = HandlerMapping.class.getName() + ".introspectTypeLevelMapping";
String URI_TEMPLATE_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".uriTemplateVariables";
String MATRIX_VARIABLES_ATTRIBUTE = HandlerMapping.class.getName() + ".matrixVariables";
String PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE = HandlerMapping.class.getName() + ".producibleMediaTypes";
// 調用 getHandler 實際上返回的是一個 HandlerExecutionChain ,這是典型的 Command 的模式的使用,這個 HandlerExecutionChain
// 不但持有 handler 本身,還包括了處理這個 HTTP 請求相關的攔截器
HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
}
HandlerExecutionChain 看起來比較簡潔,它持有一個 Interceptor 鏈和一個 handler 對象,這個 handler 對象實際上就是 HTTP 請求對應的 Controller,在持有這個 handler 對象的同時,還在 HandlerExecutionChain 中設置了一個攔截器鏈,通過這個攔截器鏈中的攔截器,可以爲 handler 對象提供功能的增強。要完成這些工作,需要對攔截器鏈和 handler 都進行配置,這些配置都是在 HandlerExecutionChain 的初始化函數中完成的。爲了維護這個攔截器鏈和 handler,handlerExecutionChain 還提供了一系列與攔截器鏈維護相關的一些操作,比如可以爲攔截器鏈增加攔截器的 addInterceptor 方法等。
public class HandlerExecutionChain {
private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);
private final Object handler;
private HandlerInterceptor[] interceptors;
private List<HandlerInterceptor> interceptorList;
private int interceptorIndex = -1;
public HandlerExecutionChain(Object handler) {
this(handler, (HandlerInterceptor[]) null);
}
public HandlerExecutionChain(Object handler, HandlerInterceptor... interceptors) {
if (handler instanceof HandlerExecutionChain) {
HandlerExecutionChain originalChain = (HandlerExecutionChain) handler;
this.handler = originalChain.getHandler();
this.interceptorList = new ArrayList<HandlerInterceptor>();
CollectionUtils.mergeArrayIntoCollection(originalChain.getInterceptors(), this.interceptorList);
CollectionUtils.mergeArrayIntoCollection(interceptors, this.interceptorList);
}
else {
this.handler = handler;
this.interceptors = interceptors;
}
}
public Object getHandler() {
return this.handler;
}
public void addInterceptor(HandlerInterceptor interceptor) {
initInterceptorList().add(interceptor);
}
public void addInterceptors(HandlerInterceptor... interceptors) {
if (!ObjectUtils.isEmpty(interceptors)) {
initInterceptorList().addAll(Arrays.asList(interceptors));
}
}
private List<HandlerInterceptor> initInterceptorList() {
if (this.interceptorList == null) {
this.interceptorList = new ArrayList<HandlerInterceptor>();
if (this.interceptors != null) {
// An interceptor array specified through the constructor
this.interceptorList.addAll(Arrays.asList(this.interceptors));
}
}
this.interceptors = null;
return this.interceptorList;
}
public HandlerInterceptor[] getInterceptors() {
if (this.interceptors == null && this.interceptorList != null) {
this.interceptors = this.interceptorList.toArray(new HandlerInterceptor[this.interceptorList.size()]);
}
return this.interceptors;
}
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = 0; i < interceptors.length; i++) {
HandlerInterceptor interceptor = interceptors[i];
if (!interceptor.preHandle(request, response, this.handler)) {
triggerAfterCompletion(request, response, null);
return false;
}
this.interceptorIndex = i;
}
}
return true;
}
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = interceptors.length - 1; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
interceptor.postHandle(request, response, this.handler, mv);
}
}
}
void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
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);
}
}
}
}
void applyAfterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response) {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = interceptors.length - 1; i >= 0; i--) {
if (interceptors[i] instanceof AsyncHandlerInterceptor) {
try {
AsyncHandlerInterceptor asyncInterceptor = (AsyncHandlerInterceptor) interceptors[i];
asyncInterceptor.afterConcurrentHandlingStarted(request, response, this.handler);
}
catch (Throwable ex) {
logger.error("Interceptor [" + interceptors[i] + "] failed in afterConcurrentHandlingStarted", ex);
}
}
}
}
}
@Override
public String toString() {
if (this.handler == null) {
return "HandlerExecutionChain with no handler";
}
StringBuilder sb = new StringBuilder();
sb.append("HandlerExecutionChain with handler [").append(this.handler).append("]");
if (!CollectionUtils.isEmpty(this.interceptorList)) {
sb.append(" and ").append(this.interceptorList.size()).append(" interceptor");
if (this.interceptorList.size() > 1) {
sb.append("s");
}
}
return sb.toString();
}
}
下面我們以 SimpleUrlHandlerMapping 說明在實際中是如何應用的,SimpleUrlHandlerMapping 定義了一個 Map 變量(自己定義一個 Map 主要有兩個作用,第一是方便配置,第二是可以在註冊前做一些預處理,如確保所以 url 都以”/“開頭),將所有的 url 和 Handler 的對應關係放在裏面,最後註冊到父類的 Map 中。
SimpleUrlHandlerMapping.java
public void initApplicationContext() throws BeansException {
super.initApplicationContext();
registerHandlers(this.urlMap);
}
protected void registerHandlers(Map<String, Object> urlMap) throws BeansException {
if (urlMap.isEmpty()) {
logger.warn("Neither 'urlMap' nor 'mappings' set on SimpleUrlHandlerMapping");
}
else {
for (Map.Entry<String, Object> entry : urlMap.entrySet()) {
String url = entry.getKey();
Object handler = entry.getValue();
// Prepend with slash if not already present.
if (!url.startsWith("/")) {
url = "/" + url;
}
// Remove whitespace from handler bean name.
if (handler instanceof String) {
handler = ((String) handler).trim();
}
registerHandler(url, handler);
}
}
}
AbstractUrlHandlerMapping 對 handler 的註冊。
AbstractUrlHandlerMapping.java
protected void registerHandler(String urlPath, Object handler) throws BeansException, IllegalStateException {
Assert.notNull(urlPath, "URL path must not be null");
Assert.notNull(handler, "Handler object must not be null");
Object resolvedHandler = handler;
// Eagerly resolve handler if referencing singleton via name.
if (!this.lazyInitHandlers && handler instanceof String) {
String handlerName = (String) handler;
if (getApplicationContext().isSingleton(handlerName)) {
resolvedHandler = getApplicationContext().getBean(handlerName);
}
}
Object mappedHandler = this.handlerMap.get(urlPath);
if (mappedHandler != null) {
if (mappedHandler != resolvedHandler) {
throw new IllegalStateException(
"Cannot map " + getHandlerDescription(handler) + " to URL path [" + urlPath +
"]: There is already " + getHandlerDescription(mappedHandler) + " mapped.");
}
}
else {
if (urlPath.equals("/")) {
if (logger.isInfoEnabled()) {
logger.info("Root mapping to " + getHandlerDescription(handler));
}
setRootHandler(resolvedHandler);
}
else if (urlPath.equals("/*")) {
if (logger.isInfoEnabled()) {
logger.info("Default mapping to " + getHandlerDescription(handler));
}
setDefaultHandler(resolvedHandler);
}
else {
this.handlerMap.put(urlPath, resolvedHandler);
if (logger.isInfoEnabled()) {
logger.info("Mapped URL path [" + urlPath + "] onto " + getHandlerDescription(handler));
}
}
}
}
HandlerMapping 完成請求和映射處理
在各種準備工作完成後,就是使用 HandlerMapping 來完成請求的映射處理了,而具體執行過程是在 AbstactHandlerMapping 中的 getHandler 來完成的。
AbstactHandlerMapping.java
@Override
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
Object handler = getHandlerInternal(request);
// 使用默認的 Handler,也就是"/"對應的 handler
if (handler == null) {
handler = getDefaultHandler();
}
// 這裏通過名稱取出對應的 Handler Bean
if (handler == null) {
return null;
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
// 這裏把 Handler 封裝到 HandlerExecutionChain 中並加上攔截器
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
if (CorsUtils.isCorsRequest(request)) {
CorsConfiguration globalConfig = this.corsConfigSource.getCorsConfiguration(request);
CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
(HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
if (interceptor instanceof MappedInterceptor) {
MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
chain.addInterceptor(mappedInterceptor.getInterceptor());
}
}
else {
chain.addInterceptor(interceptor);
}
}
return chain;
}
在取得 handler 的具體過程在 getHandlerInternal 方法中實現。這個方法接受 HTTP 請求作爲參數,它的實現在 AbstractUrlHandlerMapping 中,這個實現過程包括從 HTTP 請求中得到 URL ,並根據 URL 到 urlMapping 中獲取 handler。
AbstractUrlHandlerMapping .java
protected Object getHandlerInternal(HttpServletRequest request) throws Exception {
// 從request 中得到請求的 URL 路徑
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
// 將得到的 URL 路徑與 Handler 進行匹配
Object handler = lookupHandler(lookupPath, request);
if (handler == null) {
// We need to care for the default handler directly, since we need to
// expose the PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE for it as well.
Object rawHandler = null;
if ("/".equals(lookupPath)) {
rawHandler = getRootHandler();
}
if (rawHandler == null) {
rawHandler = getDefaultHandler();
}
if (rawHandler != null) {
// Bean name or resolved handler?
if (rawHandler instanceof String) {
String handlerName = (String) rawHandler;
rawHandler = getApplicationContext().getBean(handlerName);
}
validateHandler(rawHandler, request);
handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null);
}
}
if (handler != null && logger.isDebugEnabled()) {
logger.debug("Mapping [" + lookupPath + "] to " + handler);
}
else if (handler == null && logger.isTraceEnabled()) {
logger.trace("No handler mapping found for [" + lookupPath + "]");
}
return handler;
}
// lookupHandler 根據 URL 路徑啓動在 HandlerMap 中對 handler 的檢索,並最終返回 handler 對象
protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {
// Direct match?
Object handler = this.handlerMap.get(urlPath);
if (handler != null) {
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
validateHandler(handler, request);
return buildPathExposingHandler(handler, urlPath, urlPath, null);
}
// Pattern match?
List<String> matchingPatterns = new ArrayList<String>();
for (String registeredPattern : this.handlerMap.keySet()) {
if (getPathMatcher().match(registeredPattern, urlPath)) {
matchingPatterns.add(registeredPattern);
}
else if (useTrailingSlashMatch()) {
if (!registeredPattern.endsWith("/") && getPathMatcher().match(registeredPattern + "/", urlPath)) {
matchingPatterns.add(registeredPattern +"/");
}
}
}
String bestPatternMatch = null;
Comparator<String> patternComparator = getPathMatcher().getPatternComparator(urlPath);
if (!matchingPatterns.isEmpty()) {
Collections.sort(matchingPatterns, patternComparator);
if (logger.isDebugEnabled()) {
logger.debug("Matching patterns for request [" + urlPath + "] are " + matchingPatterns);
}
bestPatternMatch = matchingPatterns.get(0);
}
if (bestPatternMatch != null) {
handler = this.handlerMap.get(bestPatternMatch);
if (handler == null) {
Assert.isTrue(bestPatternMatch.endsWith("/"));
handler = this.handlerMap.get(bestPatternMatch.substring(0, bestPatternMatch.length() - 1));
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
validateHandler(handler, request);
String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestPatternMatch, urlPath);
// There might be multiple 'best patterns', let's make sure we have the correct URI template variables
// for all of them
Map<String, String> uriTemplateVariables = new LinkedHashMap<String, String>();
for (String matchingPattern : matchingPatterns) {
if (patternComparator.compare(bestPatternMatch, matchingPattern) == 0) {
Map<String, String> vars = getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath);
Map<String, String> decodedVars = getUrlPathHelper().decodePathVariables(request, vars);
uriTemplateVariables.putAll(decodedVars);
}
}
if (logger.isDebugEnabled()) {
logger.debug("URI Template variables for request [" + urlPath + "] are " + uriTemplateVariables);
}
return buildPathExposingHandler(handler, bestPatternMatch, pathWithinMapping, uriTemplateVariables);
}
// No handler found...
return null;
}
至此,HTTP 請求的解析和匹配 Handler 過程就全部完成了,剩下的就是 HTTP 請求的分發處理了。
Spring MVC 對 HTTP 請求的分發處理
讓我們重回到 DispatcherServlet,毫無疑問,它是 Spring MVC 中非常重要的一個類,他不僅僅建立了自己的持有 Ioc 容器,還肩負請求分佈處理的任務。而 HTTP 的請求發佈處理是在 doService 方法中完成的。
DispatcherServlet.java
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));
}
}
}
// 對 HTTP 請求參數進行處理
request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());
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 {
// 這裏是 doDispatch 的分發請求的人口
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);
}
}
}
}
對於請求的實際處理是由 doDispatch() 來完成的,這個方法很長,但過程簡單明瞭。這個 doDispatch 方法是 DispatcherServlet 完成 Dispatcher 的主要方法,包括準備 ModelAndView,調用 getHandler 來響應 HTTP 請求,然後通過執行 Handler 的處理來得到返回的 ModelAndView 結果,最後把這個 ModelAndView 對象交給相應的視圖對象去呈現。這裏是 MVC 模式的核心地區:
DispatcherServlet.java
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
// 這裏爲視圖準備好一個 ModelAndView,這個 ModelAndView 持有 handler 處理請求的結果
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// 根據請求得到對應的 handler,handler 的註冊以及 getHandler 的實現
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// 調用 Handler 的地方
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
String method = request.getMethod();
boolean isGet = "GET".equals(method);
// 判斷是否需要進行視圖的翻譯和轉換
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;
}
// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, 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);
}
}
}
}
這裏是與 MVC 框架最緊密相關的代碼,得到 HTTP 請求對應的 HandlerExecutionChain ,執行 handler 並把模型數據展現到視圖中去。
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;
}
其實,這個方法執行結束,MVC 框架中的 Controller 和 定義的一個攔截器鏈已經包含在其中了。然後,需要執行的就是返回適配的結果了。
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
// 對持有的所有 adapter 進行匹配
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");
}
這裏的 handler 是不是 Controller 接口的實現,可以通過 HandlerAdapter 來了解這個適配的過程。而具體的適配過程,我們以 SimpleControllerHandlerAdapter 的實現來說明。
public class SimpleControllerHandlerAdapter implements HandlerAdapter {
// 判斷將要調用的 handler 是不是 Controller.
@Override
public boolean supports(Object handler) {
return (handler instanceof Controller);
}
@Override
public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return ((Controller) handler).handleRequest(request, response);
}
@Override
public long getLastModified(HttpServletRequest request, Object handler) {
if (handler instanceof LastModified) {
return ((LastModified) handler).getLastModified(request);
}
return -1L;
}
}
得到 handler 對象,然後調用 handler 對象中的 HTTP 進行動作的響應。而具體的業務邏輯則被封裝在 handler 中,由這些邏輯對 HTTP 請求進行相應的處理,從而生成所需要的數據,並把這些數據封裝到 ModelAndView 對象中。最後,通過 handler 的 handlerRequest 方法觸發完成,然後交給 MVC 的 View 部分處理。至此,Spring MVC 的主要邏輯就完成了。前面已經,分析了,MVC 的 C 和 M 部分。下面就是 View 部分的分析了。