DispatcherServlet的邏輯處理
FrameworkServlet重寫了HttpServlet的doGet，doPost方法
@Override
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
/**
* Delegate POST requests to {@link #processRequest}.
* @see #doService
*/
@Override
protected final void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
交由processRequest處理
/**
* Process this request, publishing an event regardless of the outcome.
* <p>The actual event handling is performed by the abstract
* {@link #doService} template method.
*/
protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
long startTime = System.currentTimeMillis();
Throwable failureCause = null;
LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
LocaleContext localeContext = buildLocaleContext(request);
RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
initContextHolders(request, localeContext, requestAttributes);
try {
doService(request, response);
}
catch (ServletException | IOException ex) {
failureCause = ex;
throw ex;
}
catch (Throwable ex) {
failureCause = ex;
throw new NestedServletException("Request processing failed", ex);
}
finally {
resetContextHolders(request, previousLocaleContext, previousAttributes);
if (requestAttributes != null) {
requestAttributes.requestCompleted();
}
logResult(request, response, failureCause, asyncManager);
publishRequestHandledEvent(request, response, startTime, failureCause);
}
}
- 為了保證目前線程的LocaleContext、RequestAttributes可以在目前請求後恢複，提取這兩個屬性
- 将這兩個屬性綁定到目前線程
- 委托給doService處理
- 請求解說後恢複線程到原始狀态
- 無論成功失敗釋出事件通知
/**
* 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 {
logRequest(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<>();
Enumeration<?> attrNames = request.getAttributeNames();
while (attrNames.hasMoreElements()) {
String attrName = (String) attrNames.nextElement();
if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
attributesSnapshot.put(attrName, request.getAttribute(attrName));
}
}
}
// Make framework objects available to handlers and view objects.
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());
if (this.flashMapManager != null) {
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 {
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);
}
}
}
}
将已經初始化的輔助工具變量設定到request中
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) {
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 (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;
}
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);
}
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 {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
- 如果是Multipart轉化為MultipartHttpServletRequest
- 根據request擷取對應的handler，系統啟動時就會将映射類型的bean注冊到this.handlerMappings變量，對其進行周遊封裝處理
- 根據目前handler尋找相應的handlerAdapter
- Last-Modified緩存機制進行緩存處理
- HandlerInterceptor的處理，在這個攔截器的preHandler()方法中，記錄了起始時間，并将它儲存到請求屬性中。這個方法應該傳回true，允許DispatcherServlet繼續處理請求
- 通過擴充卡中轉調用Handler并傳回視圖
- 處理結果
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);
}
}
// Did the handler return a view to render?
if (mv != null && !mv.wasCleared()) {
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) {
mappedHandler.triggerAfterCompletion(request, response, null);
}
}
- 異常處理
- 根據視圖跳轉頁面
/**
* Render the given ModelAndView.
* <p>This is the last stage in handling a request. It may involve resolving the view by name.
* @param mv the ModelAndView to render
* @param request current HTTP servlet request
* @param response current HTTP servlet response
* @throws ServletException if view is missing or cannot be resolved
* @throws Exception if there's a problem rendering the view
*/
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) {
// We need to resolve the view name.
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());
}
view.render(mv.getModelInternal(), request, response);
}
catch (Exception ex) {
if (logger.isDebugEnabled()) {
logger.debug("Error rendering view [" + view + "]", ex);
}
throw ex;
}
}
- 解析視圖名稱
@Override
@Nullable
public View resolveViewName(String viewName, Locale locale) throws Exception {
if (!isCache()) {
return createView(viewName, locale);
}
else {
Object cacheKey = getCacheKey(viewName, locale);
View view = this.viewAccessCache.get(cacheKey);
if (view == null) {
synchronized (this.viewCreationCache) {
view = this.viewCreationCache.get(cacheKey);
if (view == null) {
// Ask the subclass to create the View object.
view = createView(viewName, locale);
if (view == null && this.cacheUnresolved) {
view = UNRESOLVED_VIEW;
}
if (view != null) {
this.viewAccessCache.put(cacheKey, view);
this.viewCreationCache.put(cacheKey, view);
}
}
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace(formatKey(cacheKey) + "served from cache");
}
}
return (view != UNRESOLVED_VIEW ? view : null);
}
}
1）不存在緩存直接建立視圖
2）存在從緩存中提取
父類UrlBasedViewResolver中重寫了createView
@Override
protected View createView(String viewName, Locale locale) throws Exception {
// If this resolver is not supposed to handle the given view,
// return null to pass on to the next resolver in the chain.
if (!canHandle(viewName, locale)) {
return null;
}
// Check for special "redirect:" prefix.
if (viewName.startsWith(REDIRECT_URL_PREFIX)) {
String redirectUrl = viewName.substring(REDIRECT_URL_PREFIX.length());
RedirectView view = new RedirectView(redirectUrl,
isRedirectContextRelative(), isRedirectHttp10Compatible());
String[] hosts = getRedirectHosts();
if (hosts != null) {
view.setHosts(hosts);
}
return applyLifecycleMethods(REDIRECT_URL_PREFIX, view);
}
// Check for special "forward:" prefix.
if (viewName.startsWith(FORWARD_URL_PREFIX)) {
String forwardUrl = viewName.substring(FORWARD_URL_PREFIX.length());
InternalResourceView view = new InternalResourceView(forwardUrl);
return applyLifecycleMethods(FORWARD_URL_PREFIX, view);
}
// Else fall back to superclass implementation: calling loadView.
return super.createView(viewName, locale);
}
1）處理重定向字首
2）處理轉發字首
protected View createView(String viewName, Locale locale) throws Exception {
return loadView(viewName, locale);
}
protected View loadView(String viewName, Locale locale) throws Exception {
AbstractUrlBasedView view = buildView(viewName);
View result = applyLifecycleMethods(viewName, view);
return (view.checkResource(locale) ? result : null);
}
protected AbstractUrlBasedView buildView(String viewName) throws Exception {
Class<?> viewClass = getViewClass();
Assert.state(viewClass != null, "No view class");
AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(viewClass);
view.setUrl(getPrefix() + viewName + getSuffix());
String contentType = getContentType();
if (contentType != null) {
view.setContentType(contentType);
}
view.setRequestContextAttribute(getRequestContextAttribute());
view.setAttributesMap(getAttributesMap());
Boolean exposePathVariables = getExposePathVariables();
if (exposePathVariables != null) {
view.setExposePathVariables(exposePathVariables);
}
Boolean exposeContextBeansAsAttributes = getExposeContextBeansAsAttributes();
if (exposeContextBeansAsAttributes != null) {
view.setExposeContextBeansAsAttributes(exposeContextBeansAsAttributes);
}
String[] exposedContextBeanNames = getExposedContextBeanNames();
if (exposedContextBeanNames != null) {
view.setExposedContextBeanNames(exposedContextBeanNames);
}
return view;
}
- 頁面跳轉
/**
* Prepares the view given the specified model, merging it with static
* attributes and a RequestContext attribute, if necessary.
* Delegates to renderMergedOutputModel for the actual rendering.
* @see #renderMergedOutputModel
*/
@Override
public void render(@Nullable Map<String, ?> model, HttpServletRequest request,
HttpServletResponse response) throws Exception {
if (logger.isDebugEnabled()) {
logger.debug("View " + formatViewName() +
", model " + (model != null ? model : Collections.emptyMap()) +
(this.staticAttributes.isEmpty() ? "" : ", static attributes " + this.staticAttributes));
}
Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
prepareResponse(request, response);
renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
}
/**
* Creates a combined output Map (never {@code null}) that includes dynamic values and static attributes.
* Dynamic values take precedence over static attributes.
*/
protected Map<String, Object> createMergedOutputModel(@Nullable Map<String, ?> model,
HttpServletRequest request, HttpServletResponse response) {
@SuppressWarnings("unchecked")
Map<String, Object> pathVars = (this.exposePathVariables ?
(Map<String, Object>) request.getAttribute(View.PATH_VARIABLES) : null);
// Consolidate static and dynamic model attributes.
int size = this.staticAttributes.size();
size += (model != null ? model.size() : 0);
size += (pathVars != null ? pathVars.size() : 0);
Map<String, Object> mergedModel = new LinkedHashMap<>(size);
mergedModel.putAll(this.staticAttributes);
if (pathVars != null) {
mergedModel.putAll(pathVars);
}
if (model != null) {
mergedModel.putAll(model);
}
// Expose RequestContext?
if (this.requestContextAttribute != null) {
mergedModel.put(this.requestContextAttribute, createRequestContext(request, response, mergedModel));
}
return mergedModel;
}
處理頁面跳轉
protected void renderMergedOutputModel(
Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
// Expose the model object as request attributes.
exposeModelAsRequestAttributes(model, request);
// Expose helpers as request attributes, if any.
exposeHelpers(request);
// Determine the path for the request dispatcher.
String dispatcherPath = prepareForRendering(request, response);
// Obtain a RequestDispatcher for the target resource (typically a JSP).
RequestDispatcher rd = getRequestDispatcher(request, dispatcherPath);
if (rd == null) {
throw new ServletException("Could not get RequestDispatcher for [" + getUrl() +
"]: Check that the corresponding file exists within your web application archive!");
}
// If already included or response already committed, perform include, else forward.
if (useInclude(request, response)) {
response.setContentType(getContentType());
if (logger.isDebugEnabled()) {
logger.debug("Including [" + getUrl() + "]");
}
rd.include(request, response);
}
else {
// Note: The forwarded resource is supposed to determine the content type itself.
if (logger.isDebugEnabled()) {
logger.debug("Forwarding to [" + getUrl() + "]");
}
rd.forward(request, response);
}
}
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