相信spring-mvc这种被玩坏了的架构理念，大家都烂熟于胸了，不过还是想来扒一扒他的细节。
一个http请求，怎么样被 spring 接收，又怎样做出响应呢？
一般地，我们会配置一个 web.xml，然后开始代码之旅。
在 web.xml 中配置 servlet-mapping, 将请求转发到 DispatcherServlet, 那么我们认为 DispatcherServlet 是我们的第一棒交接者！
<servlet> <servlet-name>springMVC</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>classpath:applicationContext.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>springMVC</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping>
// tomcat 接到http请求后，会主动创建一个servlet, 然后调用进应用代码中, 创建的代码如下
// Allocate a servlet instance to process this request try { if (!unavailable) { servlet = wrapper.allocate(); } } catch (ServletException e) { wrapper.getLogger().error(sm.getString("applicationDispatcher.allocateException", wrapper.getName()), StandardWrapper.getRootCause(e)); servletException = e; } catch (Throwable e) { ExceptionUtils.handleThrowable(e); wrapper.getLogger().error(sm.getString("applicationDispatcher.allocateException", wrapper.getName()), e); servletException = new ServletException (sm.getString("applicationDispatcher.allocateException", wrapper.getName()), e); servlet = null; }
// org.apache.catalina.core.StandardWrapper.allocate(), 创建 servlet,
/**
* Allocate an initialized instance of this Servlet that is ready to have
* its <code>service()</code> method called. If the servlet class does
* not implement <code>SingleThreadModel</code>, the (only) initialized
* instance may be returned immediately. If the servlet class implements
* <code>SingleThreadModel</code>, the Wrapper implementation must ensure
* that this instance is not allocated again until it is deallocated by a
* call to <code>deallocate()</code>.
*
* @exception ServletException if the servlet init() method threw
* an exception
* @exception ServletException if a loading error occurs
*/
@Override
public Servlet allocate() throws ServletException {
// If we are currently unloading this servlet, throw an exception
if (unloading) {
throw new ServletException(sm.getString("standardWrapper.unloading", getName()));
}
boolean newInstance = false;
// If not SingleThreadedModel, return the same instance every time
if (!singleThreadModel) {
// Load and initialize our instance if necessary
if (instance == null || !instanceInitialized) {
synchronized (this) {
if (instance == null) {
try {
if (log.isDebugEnabled()) {
log.debug("Allocating non-STM instance");
}
// Note: We don't know if the Servlet implements
// SingleThreadModel until we have loaded it.
instance = loadServlet();
newInstance = true;
if (!singleThreadModel) {
// For non-STM, increment here to prevent a race
// condition with unload. Bug 43683, test case
// #3
countAllocated.incrementAndGet();
}
} catch (ServletException e) {
throw e;
} catch (Throwable e) {
ExceptionUtils.handleThrowable(e);
throw new ServletException(sm.getString("standardWrapper.allocate"), e);
}
}
if (!instanceInitialized) {
initServlet(instance);
}
}
}
if (singleThreadModel) {
if (newInstance) {
// Have to do this outside of the sync above to prevent a
// possible deadlock
synchronized (instancePool) {
instancePool.push(instance);
nInstances++;
}
}
} else {
if (log.isTraceEnabled()) {
log.trace(" Returning non-STM instance");
}
// For new instances, count will have been incremented at the
// time of creation
if (!newInstance) {
countAllocated.incrementAndGet();
}
return instance;
}
}
synchronized (instancePool) {
while (countAllocated.get() >= nInstances) {
// Allocate a new instance if possible, or else wait
if (nInstances < maxInstances) {
try {
instancePool.push(loadServlet());
nInstances++;
} catch (ServletException e) {
throw e;
} catch (Throwable e) {
ExceptionUtils.handleThrowable(e);
throw new ServletException(sm.getString("standardWrapper.allocate"), e);
}
} else {
try {
instancePool.wait();
} catch (InterruptedException e) {
// Ignore
}
}
}
if (log.isTraceEnabled()) {
log.trace(" Returning allocated STM instance");
}
countAllocated.incrementAndGet();
return instancePool.pop();
}
}
// 最后，会先调用 filter, 完成之后再调用 servlet.service()
private void internalDoFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException { // Call the next filter if there is one if (pos < n) { ApplicationFilterConfig filterConfig = filters[pos++]; try { Filter filter = filterConfig.getFilter(); if (request.isAsyncSupported() && "false".equalsIgnoreCase( filterConfig.getFilterDef().getAsyncSupported())) { request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE); } if( Globals.IS_SECURITY_ENABLED ) { final ServletRequest req = request; final ServletResponse res = response; Principal principal = ((HttpServletRequest) req).getUserPrincipal(); Object[] args = new Object[]{req, res, this}; SecurityUtil.doAsPrivilege ("doFilter", filter, classType, args, principal); } else { filter.doFilter(request, response, this); } } catch (IOException | ServletException | RuntimeException e) { throw e; } catch (Throwable e) { e = ExceptionUtils.unwrapInvocationTargetException(e); ExceptionUtils.handleThrowable(e); throw new ServletException(sm.getString("filterChain.filter"), e); } return; } // We fell off the end of the chain -- call the servlet instance try { if (ApplicationDispatcher.WRAP_SAME_OBJECT) { lastServicedRequest.set(request); lastServicedResponse.set(response); } if (request.isAsyncSupported() && !servletSupportsAsync) { request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE); } // Use potentially wrapped request from this point if ((request instanceof HttpServletRequest) && (response instanceof HttpServletResponse) && Globals.IS_SECURITY_ENABLED ) { final ServletRequest req = request; final ServletResponse res = response; Principal principal = ((HttpServletRequest) req).getUserPrincipal(); Object[] args = new Object[]{req, res}; SecurityUtil.doAsPrivilege("service", servlet, classTypeUsedInService, args, principal); } else { servlet.service(request, response); } } catch (IOException | ServletException | RuntimeException e) { throw e; } catch (Throwable e) { e = ExceptionUtils.unwrapInvocationTargetException(e); ExceptionUtils.handleThrowable(e); throw new ServletException(sm.getString("filterChain.servlet"), e); } finally { if (ApplicationDispatcher.WRAP_SAME_OBJECT) { lastServicedRequest.set(null); lastServicedResponse.set(null); } } }
// 现在，到了 DispatcherServlet 出场了，由 DispatcherServlet 的父类 org.springframework.web.servlet.FrameworkServlet.service()接力， 开始处理
/** * Override the parent class implementation in order to intercept PATCH requests. */ @Override protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { HttpMethod httpMethod = HttpMethod.resolve(request.getMethod()); if (HttpMethod.PATCH == httpMethod || httpMethod == null) { processRequest(request, response); } else { // 交由 HttpServlet.service() 处理，转发 doGet,doPost 等等方法 super.service(request, response); } } // 父类 HttpServlet.service(), 只负责转发请求，由子类进行相应处理 protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String method = req.getMethod(); if (method.equals(METHOD_GET)) { long lastModified = getLastModified(req); if (lastModified == -1) { // servlet doesn't support if-modified-since, no reason // to go through further expensive logic doGet(req, resp); } else { long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE); if (ifModifiedSince < lastModified) { // If the servlet mod time is later, call doGet() // Round down to the nearest second for a proper compare // A ifModifiedSince of -1 will always be less maybeSetLastModified(resp, lastModified); doGet(req, resp); } else { resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED); } } } else if (method.equals(METHOD_HEAD)) { long lastModified = getLastModified(req); maybeSetLastModified(resp, lastModified); doHead(req, resp); } else if (method.equals(METHOD_POST)) { doPost(req, resp); } else if (method.equals(METHOD_PUT)) { doPut(req, resp); } else if (method.equals(METHOD_DELETE)) { doDelete(req, resp); } else if (method.equals(METHOD_OPTIONS)) { doOptions(req,resp); } else if (method.equals(METHOD_TRACE)) { doTrace(req,resp); } else { // // Note that this means NO servlet supports whatever // method was requested, anywhere on this server. // String errMsg = lStrings.getString("http.method_not_implemented"); Object[] errArgs = new Object[1]; errArgs[0] = method; errMsg = MessageFormat.format(errMsg, errArgs); resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg); } }
// 比如 FrameworkServlet.doGet()/doXXX() 方法重写, 调用 processRequest()
/** * Delegate GET requests to processRequest/doService. * <p>Will also be invoked by HttpServlet's default implementation of {@code doHead}, * with a {@code NoBodyResponse} that just captures the content length. * @see #doService * @see #doHead */ @Override protected final void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { processRequest(request, response); }
// FrameworkServlet.processRequest() 做一些全局设置，然后交由 doService() 进行具体处理, doService() 由子类实现,也即 DispatcherServlet.doService()
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 { // 具体处理，交由 DispatcherServlet 处理 doService(request, response); } catch (ServletException ex) { failureCause = ex; throw ex; } catch (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) { // 请求完成回调 requestAttributes.requestCompleted(); } if (logger.isDebugEnabled()) { if (failureCause != null) { this.logger.debug("Could not complete request", failureCause); } else { if (asyncManager.isConcurrentHandlingStarted()) { logger.debug("Leaving response open for concurrent processing"); } else { this.logger.debug("Successfully completed request"); } } } // 发布完成事件 publishRequestHandledEvent(request, response, startTime, failureCause); } }
// locale 上下文管理
private void initContextHolders( HttpServletRequest request, LocaleContext localeContext, RequestAttributes requestAttributes) { // private static final ThreadLocal<LocaleContext> localeContextHolder = new NamedThreadLocal<LocaleContext>("LocaleContext"); if (localeContext != null) { LocaleContextHolder.setLocaleContext(localeContext, this.threadContextInheritable); } // private static final ThreadLocal<RequestAttributes> requestAttributesHolder = new NamedThreadLocal<RequestAttributes>("Request attributes"); if (requestAttributes != null) { RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable); } if (logger.isTraceEnabled()) { logger.trace("Bound request context to thread: " + request); } }
// org.springframework.web.servlet.DispatcherServlet, 进行具体请求转发
/** * 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 { 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(DEFAULT_STRATEGIES_PREFIX)) { attributesSnapshot.put(attrName, request.getAttribute(attrName)); } } } // Make framework objects available to handlers and view objects. // 设备各种处理器到 request 中 // 上下文管理 request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext()); // locale 管理 request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver); // themeResolver 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 { 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); } } } }
// doDispatch(), 实际分发方法
/** * Process the actual dispatching to the handler. * <p>The handler will be obtained by applying the servlet's HandlerMappings in order. * The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters * to find the first that supports the handler class. * <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers * themselves to decide which methods are acceptable. * @param request current HTTP request * @param response current HTTP response * @throws Exception in case of any kind of processing failure */ 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 { // 封装 multipart 文件上传，如果是文件上传类，则将其封装为 MultipartHttpServletRequest, 以便后续直接使用 processedRequest = checkMultipart(request); multipartRequestParsed = (processedRequest != request); // 获取具体uri业务处理器,即 由 RequestMapping 设置的路径 mappedHandler = getHandler(processedRequest); if (mappedHandler == null || mappedHandler.getHandler() == null) { // 如果没有找到 handler 则结束处理 noHandlerFound(processedRequest, response); return; } // Determine handler adapter for the current request. HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler()); // 对GET|HEAD 进行 last-modified 进行检测 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; } } // 进行处理器前置调用，如果未通过，则结束 if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } // Actually invoke the handler. // 调用业务处理 mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); if (asyncManager.isConcurrentHandlingStarted()) { return; } // 设置 view applyDefaultViewName(processedRequest, mv); // 后置处理 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); } // 最后再处理一次结果，如果有必要的话 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 { // 清理环境 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); } } } }
// multipart 检测，需设置 multipartResolver, 方能转换，否则直接返回原始请求
/** * Convert the request into a multipart request, and make multipart resolver available. * <p>If no multipart resolver is set, simply use the existing request. * @param request current HTTP request * @return the processed request (multipart wrapper if necessary) * @see MultipartResolver#resolveMultipart */ protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException { if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) { if (WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class) != null) { logger.debug("Request is already a MultipartHttpServletRequest - if not in a forward, " + "this typically results from an additional MultipartFilter in web.xml"); } else if (hasMultipartException(request) ) { logger.debug("Multipart resolution failed for current request before - " + "skipping re-resolution for undisturbed error rendering"); } else { try { // 调用 multipartResolver.resolveMultipart(), 由 resolver 进行文件转换处理 return this.multipartResolver.resolveMultipart(request); } catch (MultipartException ex) { if (request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) != null) { logger.debug("Multipart resolution failed for error dispatch", ex); // Keep processing error dispatch with regular request handle below } else { throw ex; } } } } // If not returned before: return original request. return request; }
// 关键: 获取handler, 以待调用
/** * 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 { // handlerMappings 中保存了所有可用的路由 for (HandlerMapping hm : this.handlerMappings) { if (logger.isTraceEnabled()) { logger.trace( "Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'"); } // 由具体的 HandlerMapping 去解析自己的映射 HandlerExecutionChain handler = hm.getHandler(request); if (handler != null) { return handler; } } return null; } // org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping // org.springframework.web.servlet.handler.AbstractHandlerMapping.getHandler() /** * Look up a handler for the given request, falling back to the default * handler if no specific one is found. * @param request current HTTP request * @return the corresponding handler instance, or the default handler * @see #getHandlerInternal */ @Override public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { // 获取 handlerMethod 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 = getApplicationContext().getBean(handlerName); } // 获取 handler 链 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; } // org.springframework.web.servlet.handler.AbstractHandlerMethodMapping.getHandlerInternal(), 查找 handler /** * Look up a handler method for the given request. */ @Override protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception { // UrlHelper.getLookupPathForRequest() 进行路径分析 String lookupPath = getUrlPathHelper().getLookupPathForRequest(request); if (logger.isDebugEnabled()) { logger.debug("Looking up handler method for path " + lookupPath); } // 加锁读取 this.mappingRegistry.acquireReadLock(); try { // 根据path查找 handlerMethod HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request); if (logger.isDebugEnabled()) { if (handlerMethod != null) { logger.debug("Returning handler method [" + handlerMethod + "]"); } else { logger.debug("Did not find handler method for [" + lookupPath + "]"); } } // 找到匹配后，将 handler 通过 bean 查找方式包装进 HandlerMethod 中返回 return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null); } finally { this.mappingRegistry.releaseReadLock(); } }
// 更细节的查询 handler 动作
// org.springframework.web.util.UrlPathHelper /** * Return the mapping lookup path for the given request, within the current * servlet mapping if applicable, else within the web application. * <p>Detects include request URL if called within a RequestDispatcher include. * @param request current HTTP request * @return the lookup path * @see #getPathWithinApplication * @see #getPathWithinServletMapping */ public String getLookupPathForRequest(HttpServletRequest request) { // Always use full path within current servlet context? if (this.alwaysUseFullPath) { return getPathWithinApplication(request); } // Else, use path within current servlet mapping if applicable String rest = getPathWithinServletMapping(request); if (!"".equals(rest)) { return rest; } else { // 返回 /hello/test return getPathWithinApplication(request); } } // /** * Return the path within the servlet mapping for the given request, * i.e. the part of the request's URL beyond the part that called the servlet, * or "" if the whole URL has been used to identify the servlet. * <p>Detects include request URL if called within a RequestDispatcher include. * <p>E.g.: servlet mapping = "/*"; request URI = "/test/a" -> "/test/a". * <p>E.g.: servlet mapping = "/"; request URI = "/test/a" -> "/test/a". * <p>E.g.: servlet mapping = "/test/*"; request URI = "/test/a" -> "/a". * <p>E.g.: servlet mapping = "/test"; request URI = "/test" -> "". * <p>E.g.: servlet mapping = "/*.test"; request URI = "/a.test" -> "". * @param request current HTTP request * @return the path within the servlet mapping, or "" */ public String getPathWithinServletMapping(HttpServletRequest request) { String pathWithinApp = getPathWithinApplication(request); String servletPath = getServletPath(request); String sanitizedPathWithinApp = getSanitizedPath(pathWithinApp); String path; // If the app container sanitized the servletPath, check against the sanitized version if (servletPath.contains(sanitizedPathWithinApp)) { path = getRemainingPath(sanitizedPathWithinApp, servletPath, false); } else { path = getRemainingPath(pathWithinApp, servletPath, false); } if (path != null) { // Normal case: URI contains servlet path. return path; } else { // Special case: URI is different from servlet path. String pathInfo = request.getPathInfo(); if (pathInfo != null) { // Use path info if available. Indicates index page within a servlet mapping? // e.g. with index page: URI="/", servletPath="/index.html" return pathInfo; } if (!this.urlDecode) { // No path info... (not mapped by prefix, nor by extension, nor "/*") // For the default servlet mapping (i.e. "/"), urlDecode=false can // cause issues since getServletPath() returns a decoded path. // If decoding pathWithinApp yields a match just use pathWithinApp. path = getRemainingPath(decodeInternal(request, pathWithinApp), servletPath, false); if (path != null) { return pathWithinApp; } } // Otherwise, use the full servlet path. return servletPath; } } // org.springframework.web.servlet.handler.AbstractHandlerMethodMapping /** * Look up the best-matching handler method for the current request. * If multiple matches are found, the best match is selected. * @param lookupPath mapping lookup path within the current servlet mapping * @param request the current request * @return the best-matching handler method, or {@code null} if no match * @see #handleMatch(Object, String, HttpServletRequest) * @see #handleNoMatch(Set, String, HttpServletRequest) */ protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception { List<Match> matches = new ArrayList<Match>(); List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath); if (directPathMatches != null) { // 添加到匹配中，考虑不止一个匹配 addMatchingMappings(directPathMatches, matches, request); } if (matches.isEmpty()) { // No choice but to go through all mappings... addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request); } if (!matches.isEmpty()) { // 如果有多个匹配，进行优先级排序，判断是否可用，然后取第一个作为最终的 handler Comparator<Match> comparator = new MatchComparator(getMappingComparator(request)); Collections.sort(matches, comparator); if (logger.isTraceEnabled()) { logger.trace("Found " + matches.size() + " matching mapping(s) for [" + lookupPath + "] : " + matches); } Match bestMatch = matches.get(0); if (matches.size() > 1) { if (CorsUtils.isPreFlightRequest(request)) { return PREFLIGHT_AMBIGUOUS_MATCH; } Match secondBestMatch = matches.get(1); if (comparator.compare(bestMatch, secondBestMatch) == 0) { Method m1 = bestMatch.handlerMethod.getMethod(); Method m2 = secondBestMatch.handlerMethod.getMethod(); throw new IllegalStateException("Ambiguous handler methods mapped for HTTP path '" + request.getRequestURL() + "': {" + m1 + ", " + m2 + "}"); } } // 解析参数到 handlerMethod 中 handleMatch(bestMatch.mapping, lookupPath, request); return bestMatch.handlerMethod; } else { return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request); } } // AbstractHandlerMethodMapping$MappingRegistry.getMappingsByUrl() /** * Return matches for the given URL path. Not thread-safe. * @see #acquireReadLock() */ public List<T> getMappingsByUrl(String urlPath) { // private final MultiValueMap<String, T> urlLookup = new LinkedMultiValueMap<String, T>(); // 内部使用 Map<K, List<V>> targetMap; 进行保存关系映射 return this.urlLookup.get(urlPath); } // AbstractHandlerMethodMapping, 将确实有效的mapping添加到 matches 中 private void addMatchingMappings(Collection<T> mappings, List<Match> matches, HttpServletRequest request) { for (T mapping : mappings) { // 重新严格校验路径，参数，header， 返回新的mapping T match = getMatchingMapping(mapping, request); if (match != null) { // 将 handler 放入 match // private class Match {} matches.add(new Match(match, this.mappingRegistry.getMappings().get(mapping))); } } }
// org.springframework.web.servlet.mvc.condition.HeadersRequestCondition
// org.springframework.web.servlet.mvc.method.RequestMappingInfo
// 进行参数校验，并封装返回参数信息到 RequestMappingInfo 中返回
/** * Checks if all conditions in this request mapping info match the provided request and returns * a potentially new request mapping info with conditions tailored to the current request. * <p>For example the returned instance may contain the subset of URL patterns that match to * the current request, sorted with best matching patterns on top. * @return a new instance in case all conditions match; or {@code null} otherwise */ @Override public RequestMappingInfo getMatchingCondition(HttpServletRequest request) { RequestMethodsRequestCondition methods = this.methodsCondition.getMatchingCondition(request); ParamsRequestCondition params = this.paramsCondition.getMatchingCondition(request); HeadersRequestCondition headers = this.headersCondition.getMatchingCondition(request); ConsumesRequestCondition consumes = this.consumesCondition.getMatchingCondition(request); ProducesRequestCondition produces = this.producesCondition.getMatchingCondition(request); // 其中某个不匹配，则返回 null if (methods == null || params == null || headers == null || consumes == null || produces == null) { return null; } PatternsRequestCondition patterns = this.patternsCondition.getMatchingCondition(request); if (patterns == null) { return null; } RequestConditionHolder custom = this.customConditionHolder.getMatchingCondition(request); if (custom == null) { return null; } return new RequestMappingInfo(this.name, patterns, methods, params, headers, consumes, produces, custom.getCondition()); }
/** * Expose URI template variables, matrix variables, and producible media types in the request. * @see HandlerMapping#URI_TEMPLATE_VARIABLES_ATTRIBUTE * @see HandlerMapping#MATRIX_VARIABLES_ATTRIBUTE * @see HandlerMapping#PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE */ @Override protected void handleMatch(RequestMappingInfo info, String lookupPath, HttpServletRequest request) { super.handleMatch(info, lookupPath, request); String bestPattern; Map<String, String> uriVariables; Map<String, String> decodedUriVariables; Set<String> patterns = info.getPatternsCondition().getPatterns(); if (patterns.isEmpty()) { bestPattern = lookupPath; uriVariables = Collections.emptyMap(); decodedUriVariables = Collections.emptyMap(); } else { bestPattern = patterns.iterator().next(); uriVariables = getPathMatcher().extractUriTemplateVariables(bestPattern, lookupPath); decodedUriVariables = getUrlPathHelper().decodePathVariables(request, uriVariables); } request.setAttribute(BEST_MATCHING_PATTERN_ATTRIBUTE, bestPattern); request.setAttribute(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, decodedUriVariables); if (isMatrixVariableContentAvailable()) { Map<String, MultiValueMap<String, String>> matrixVars = extractMatrixVariables(request, uriVariables); request.setAttribute(HandlerMapping.MATRIX_VARIABLES_ATTRIBUTE, matrixVars); } if (!info.getProducesCondition().getProducibleMediaTypes().isEmpty()) { Set<MediaType> mediaTypes = info.getProducesCondition().getProducibleMediaTypes(); request.setAttribute(PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE, mediaTypes); } }
// org.springframework.web.method.HandlerMethod.createWithResolvedBean(), 重新包装一个带bean实例的 HandlerMethod
/** * If the provided instance contains a bean name rather than an object instance, * the bean name is resolved before a {@link HandlerMethod} is created and returned. */ public HandlerMethod createWithResolvedBean() { Object handler = this.bean; if (this.bean instanceof String) { String beanName = (String) this.bean; // spring beans 组件 handler = this.beanFactory.getBean(beanName); } return new HandlerMethod(this, handler); }
/**
* Build a {@link HandlerExecutionChain} for the given handler, including
* applicable interceptors.
* <p>The default implementation builds a standard {@link HandlerExecutionChain}
* with the given handler, the handler mapping's common interceptors, and any
* {@link MappedInterceptor}s matching to the current request URL. Interceptors
* are added in the order they were registered. Subclasses may override this
* in order to extend/rearrange the list of interceptors.
* <p><b>NOTE:</b> The passed-in handler object may be a raw handler or a
* pre-built {@link HandlerExecutionChain}. This method should handle those
* two cases explicitly, either building a new {@link HandlerExecutionChain}
* or extending the existing chain.
* <p>For simply adding an interceptor in a custom subclass, consider calling
* {@code super.getHandlerExecutionChain(handler, request)} and invoking
* {@link HandlerExecutionChain#addInterceptor} on the returned chain object.
* @param handler the resolved handler instance (never {@code null})
* @param request current HTTP request
* @return the HandlerExecutionChain (never {@code null})
* @see #getAdaptedInterceptors()
*/
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)) {
// 取出内层的 interceptor 使用
chain.addInterceptor(mappedInterceptor.getInterceptor());
}
}
else {
chain.addInterceptor(interceptor);
}
}
return chain;
}
// 获取 adapter，适配不同类型的调用
// org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter // org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter // org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter /** * 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"); }
// mappedHandler.applyPreHandle(processedRequest, response) , 前置调用处理, interceptor 拦截调用
/** * Apply preHandle methods of registered interceptors. * @return {@code true} if the execution chain should proceed with the * next interceptor or the handler itself. Else, DispatcherServlet assumes * that this interceptor has already dealt with the response itself. */ 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]; // 接收 preHandle 返回值, false 则终止 if (!interceptor.preHandle(request, response, this.handler)) { triggerAfterCompletion(request, response, null); return false; } this.interceptorIndex = i; } } return true; }
// mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); 真正调用 handler 处理业务
// org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter
// method.AbstractHandlerMethodAdapter
/** * This implementation expects the handler to be an {@link HandlerMethod}. */ @Override public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { // 内部调用 return handleInternal(request, response, (HandlerMethod) handler); } // @Override protected ModelAndView handleInternal(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception { ModelAndView mav; // 预检查是否可支持 checkRequest(request); // 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... // invoke mav = invokeHandlerMethod(request, response, handlerMethod); } if (!response.containsHeader(HEADER_CACHE_CONTROL)) { if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) { applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers); } else { prepareResponse(response); } } return mav; }
//org.springframework.web.servlet.support.WebContentGenerator.checkRequest() /** * Check the given request for supported methods and a required session, if any. * @param request current HTTP request * @throws ServletException if the request cannot be handled because a check failed * @since 4.2 */ protected final void checkRequest(HttpServletRequest request) throws ServletException { // Check whether we should support the request method. String method = request.getMethod(); if (this.supportedMethods != null && !this.supportedMethods.contains(method)) { throw new HttpRequestMethodNotSupportedException(method, this.supportedMethods); } // Check whether a session is required. if (this.requireSession && request.getSession(false) == null) { throw new HttpSessionRequiredException("Pre-existing session required but none found"); } }
// 调用 Adapter 的 handler 处理方法
/** * Invoke the {@link RequestMapping} handler method preparing a {@link ModelAndView} * if view resolution is required. * @since 4.2 * @see #createInvocableHandlerMethod(HandlerMethod) */ protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, HandlerMethod handlerMethod) throws Exception { ServletWebRequest webRequest = new ServletWebRequest(request, response); try { // 获取参数绑定工厂 WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod); // 参数解析 ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory); // createInvocableHandlerMethod, 反射调用工具类 ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod); invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers); invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers); invocableMethod.setDataBinderFactory(binderFactory); invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer); // mav ModelAndViewContainer mavContainer = new ModelAndViewContainer(); mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request)); modelFactory.initModel(webRequest, mavContainer, invocableMethod); mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect); AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response); asyncWebRequest.setTimeout(this.asyncRequestTimeout); WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); asyncManager.setTaskExecutor(this.taskExecutor); asyncManager.setAsyncWebRequest(asyncWebRequest); asyncManager.registerCallableInterceptors(this.callableInterceptors); asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors); if (asyncManager.hasConcurrentResult()) { Object result = asyncManager.getConcurrentResult(); mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0]; asyncManager.clearConcurrentResult(); if (logger.isDebugEnabled()) { logger.debug("Found concurrent result value [" + result + "]"); } invocableMethod = invocableMethod.wrapConcurrentResult(result); } // 调用业务 controller invocableMethod.invokeAndHandle(webRequest, mavContainer); if (asyncManager.isConcurrentHandlingStarted()) { return null; } // 返回 mv, jsp, 如果是 json 一类的输出，则直接返回 null return getModelAndView(mavContainer, modelFactory, webRequest); } finally { webRequest.requestCompleted(); } }
细节点的工厂类创建：
// 参数绑定工厂 private WebDataBinderFactory getDataBinderFactory(HandlerMethod handlerMethod) throws Exception { Class<?> handlerType = handlerMethod.getBeanType(); Set<Method> methods = this.initBinderCache.get(handlerType); if (methods == null) { methods = MethodIntrospector.selectMethods(handlerType, INIT_BINDER_METHODS); this.initBinderCache.put(handlerType, methods); } List<InvocableHandlerMethod> initBinderMethods = new ArrayList<InvocableHandlerMethod>(); // Global methods first for (Entry<ControllerAdviceBean, Set<Method>> entry : this.initBinderAdviceCache.entrySet()) { if (entry.getKey().isApplicableToBeanType(handlerType)) { Object bean = entry.getKey().resolveBean(); for (Method method : entry.getValue()) { initBinderMethods.add(createInitBinderMethod(bean, method)); } } } for (Method method : methods) { Object bean = handlerMethod.getBean(); initBinderMethods.add(createInitBinderMethod(bean, method)); } return createDataBinderFactory(initBinderMethods); } // 参数解析工厂 private ModelFactory getModelFactory(HandlerMethod handlerMethod, WebDataBinderFactory binderFactory) { SessionAttributesHandler sessionAttrHandler = getSessionAttributesHandler(handlerMethod); Class<?> handlerType = handlerMethod.getBeanType(); Set<Method> methods = this.modelAttributeCache.get(handlerType); if (methods == null) { methods = MethodIntrospector.selectMethods(handlerType, MODEL_ATTRIBUTE_METHODS); this.modelAttributeCache.put(handlerType, methods); } List<InvocableHandlerMethod> attrMethods = new ArrayList<InvocableHandlerMethod>(); // Global methods first for (Entry<ControllerAdviceBean, Set<Method>> entry : this.modelAttributeAdviceCache.entrySet()) { if (entry.getKey().isApplicableToBeanType(handlerType)) { Object bean = entry.getKey().resolveBean(); for (Method method : entry.getValue()) { attrMethods.add(createModelAttributeMethod(binderFactory, bean, method)); } } } for (Method method : methods) { Object bean = handlerMethod.getBean(); attrMethods.add(createModelAttributeMethod(binderFactory, bean, method)); } return new ModelFactory(attrMethods, binderFactory, sessionAttrHandler); }
// org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle()
/** * Invoke the method and handle the return value through one of the * configured {@link HandlerMethodReturnValueHandler}s. * @param webRequest the current request * @param mavContainer the ModelAndViewContainer for this request * @param providedArgs "given" arguments matched by type (not resolved) */ public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception { // 直接调用 handler Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs); // 设置响应码 setResponseStatus(webRequest); if (returnValue == null) { if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) { mavContainer.setRequestHandled(true); return; } } else if (StringUtils.hasText(getResponseStatusReason())) { mavContainer.setRequestHandled(true); return; } mavContainer.setRequestHandled(false); try { // 处理返回值 this.returnValueHandlers.handleReturnValue( returnValue, getReturnValueType(returnValue), mavContainer, webRequest); } catch (Exception ex) { if (logger.isTraceEnabled()) { logger.trace(getReturnValueHandlingErrorMessage("Error handling return value", returnValue), ex); } throw ex; } } // InvocableHandlerMethod.invokeForRequest() /** * Invoke the method after resolving its argument values in the context of the given request. * <p>Argument values are commonly resolved through {@link HandlerMethodArgumentResolver}s. * The {@code providedArgs} parameter however may supply argument values to be used directly, * i.e. without argument resolution. Examples of provided argument values include a * {@link WebDataBinder}, a {@link SessionStatus}, or a thrown exception instance. * Provided argument values are checked before argument resolvers. * @param request the current request * @param mavContainer the ModelAndViewContainer for this request * @param providedArgs "given" arguments matched by type, not resolved * @return the raw value returned by the invoked method * @exception Exception raised if no suitable argument resolver can be found, * or if the method raised an exception */ public Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception { // 获取方法参数 Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs); if (logger.isTraceEnabled()) { logger.trace("Invoking '" + ClassUtils.getQualifiedMethodName(getMethod(), getBeanType()) + "' with arguments " + Arrays.toString(args)); } // invoke Object returnValue = doInvoke(args); if (logger.isTraceEnabled()) { logger.trace("Method [" + ClassUtils.getQualifiedMethodName(getMethod(), getBeanType()) + "] returned [" + returnValue + "]"); } return returnValue; }
// 参数封装，InvocableHandlerMethod.getMethodArgumentValues()
// InvocableHandlerMethod.getMethodArgumentValues() /** * Get the method argument values for the current request. */ private Object[] getMethodArgumentValues(NativeWebRequest request, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception { MethodParameter[] parameters = getMethodParameters(); Object[] args = new Object[parameters.length]; for (int i = 0; i < parameters.length; i++) { MethodParameter parameter = parameters[i]; parameter.initParameterNameDiscovery(this.parameterNameDiscoverer); args[i] = resolveProvidedArgument(parameter, providedArgs); if (args[i] != null) { continue; } if (this.argumentResolvers.supportsParameter(parameter)) { try { args[i] = this.argumentResolvers.resolveArgument( parameter, mavContainer, request, this.dataBinderFactory); continue; } catch (Exception ex) { if (logger.isDebugEnabled()) { logger.debug(getArgumentResolutionErrorMessage("Failed to resolve", i), ex); } throw ex; } } if (args[i] == null) { throw new IllegalStateException("Could not resolve method parameter at index " + parameter.getParameterIndex() + " in " + parameter.getMethod().toGenericString() + ": " + getArgumentResolutionErrorMessage("No suitable resolver for", i)); } } return args; } // org.springframework.web.method.support.HandlerMethodArgumentResolverComposite /** * Iterate over registered {@link HandlerMethodArgumentResolver}s and invoke the one that supports it. * @throws IllegalStateException if no suitable {@link HandlerMethodArgumentResolver} is found. */ @Override public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception { HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter); if (resolver == null) { throw new IllegalArgumentException("Unknown parameter type [" + parameter.getParameterType().getName() + "]"); } return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory); } // AbstractNamedValueMethodArgumentResolver @Override public final Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception { NamedValueInfo namedValueInfo = getNamedValueInfo(parameter); MethodParameter nestedParameter = parameter.nestedIfOptional(); // 处理 key Object resolvedName = resolveStringValue(namedValueInfo.name); if (resolvedName == null) { throw new IllegalArgumentException( "Specified name must not resolve to null: [" + namedValueInfo.name + "]"); } // 获取 value Object arg = resolveName(resolvedName.toString(), nestedParameter, webRequest); if (arg == null) { if (namedValueInfo.defaultValue != null) { arg = resolveStringValue(namedValueInfo.defaultValue); } else if (namedValueInfo.required && !nestedParameter.isOptional()) { handleMissingValue(namedValueInfo.name, nestedParameter, webRequest); } arg = handleNullValue(namedValueInfo.name, arg, nestedParameter.getNestedParameterType()); } else if ("".equals(arg) && namedValueInfo.defaultValue != null) { arg = resolveStringValue(namedValueInfo.defaultValue); } if (binderFactory != null) { WebDataBinder binder = binderFactory.createBinder(webRequest, null, namedValueInfo.name); try { arg = binder.convertIfNecessary(arg, parameter.getParameterType(), parameter); } catch (ConversionNotSupportedException ex) { throw new MethodArgumentConversionNotSupportedException(arg, ex.getRequiredType(), namedValueInfo.name, parameter, ex.getCause()); } catch (TypeMismatchException ex) { throw new MethodArgumentTypeMismatchException(arg, ex.getRequiredType(), namedValueInfo.name, parameter, ex.getCause()); } } handleResolvedValue(arg, namedValueInfo.name, parameter, mavContainer, webRequest); return arg; }
// Object returnValue = doInvoke(args);
// InvocableHandlerMethod.doInvoke(), 正常返回结果，异常包装返回
/** * Invoke the handler method with the given argument values. */ protected Object doInvoke(Object... args) throws Exception { // 确保方法可调用 ReflectionUtils.makeAccessible(getBridgedMethod()); try { // 调用业务方法 return getBridgedMethod().invoke(getBean(), args); } catch (IllegalArgumentException ex) { assertTargetBean(getBridgedMethod(), getBean(), args); String text = (ex.getMessage() != null ? ex.getMessage() : "Illegal argument"); throw new IllegalStateException(getInvocationErrorMessage(text, args), ex); } catch (InvocationTargetException ex) { // Unwrap for HandlerExceptionResolvers ... Throwable targetException = ex.getTargetException(); if (targetException instanceof RuntimeException) { throw (RuntimeException) targetException; } else if (targetException instanceof Error) { throw (Error) targetException; } else if (targetException instanceof Exception) { throw (Exception) targetException; } else { String text = getInvocationErrorMessage("Failed to invoke handler method", args); throw new IllegalStateException(text, targetException); } } }
// 至此业务方法终于调用完成
// 接下来，处理返回值
// this.returnValueHandlers.handleReturnValue( // returnValue, getReturnValueType(returnValue), mavContainer, webRequest); // org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue() /** * Iterate over registered {@link HandlerMethodReturnValueHandler}s and invoke the one that supports it. * @throws IllegalStateException if no suitable {@link HandlerMethodReturnValueHandler} is found. */ @Override public void handleReturnValue(Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception { HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType); if (handler == null) { throw new IllegalArgumentException("Unknown return value type: " + returnType.getParameterType().getName()); } handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest); } // 返回值处理器 // org.springframework.web.servlet.mvc.method.annotation.ModelAndViewMethodReturnValueHandler // org.springframework.web.method.annotation.ModelMethodProcessor // org.springframework.web.servlet.mvc.method.annotation.ViewMethodReturnValueHandler // org.springframework.web.servlet.mvc.method.annotation.ResponseBodyEmitterReturnValueHandler // org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBodyReturnValueHandler // org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor // org.springframework.web.servlet.mvc.method.annotation.HttpHeadersReturnValueHandler // org.springframework.web.servlet.mvc.method.annotation.CallableMethodReturnValueHandler // org.springframework.web.servlet.mvc.method.annotation.DeferredResultMethodReturnValueHandler // org.springframework.web.servlet.mvc.method.annotation.AsyncTaskMethodReturnValueHandler // org.springframework.web.method.annotation.ModelAttributeMethodProcessor // org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor // org.springframework.web.servlet.mvc.method.annotation.ViewNameMethodReturnValueHandler // org.springframework.web.method.annotation.MapMethodProcessor // org.springframework.web.method.annotation.ModelAttributeMethodProcessor private HandlerMethodReturnValueHandler selectHandler(Object value, MethodParameter returnType) { boolean isAsyncValue = isAsyncReturnValue(value, returnType); for (HandlerMethodReturnValueHandler handler : this.returnValueHandlers) { if (isAsyncValue && !(handler instanceof AsyncHandlerMethodReturnValueHandler)) { continue; } // return Callable.class.isAssignableFrom(returnType.getParameterType()); // return (AnnotatedElementUtils.hasAnnotation(returnType.getContainingClass(), ResponseBody.class) || // returnType.hasMethodAnnotation(ResponseBody.class)); if (handler.supportsReturnType(returnType)) { return handler; } } return null; } // org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(), 处理返回结果 @Override public void handleReturnValue(Object returnValue, MethodParameter returnType, ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException { mavContainer.setRequestHandled(true); ServletServerHttpRequest inputMessage = createInputMessage(webRequest); ServletServerHttpResponse outputMessage = createOutputMessage(webRequest); // 写返回值 // Try even with null return value. ResponseBodyAdvice could get involved. writeWithMessageConverters(returnValue, returnType, inputMessage, outputMessage); } /** * Creates a new {@link HttpOutputMessage} from the given {@link NativeWebRequest}. * @param webRequest the web request to create an output message from * @return the output message */ protected ServletServerHttpResponse createOutputMessage(NativeWebRequest webRequest) { HttpServletResponse response = webRequest.getNativeResponse(HttpServletResponse.class); return new ServletServerHttpResponse(response); } /** * Writes the given return type to the given output message. * @param value the value to write to the output message * @param returnType the type of the value * @param inputMessage the input messages. Used to inspect the {@code Accept} header. * @param outputMessage the output message to write to * @throws IOException thrown in case of I/O errors * @throws HttpMediaTypeNotAcceptableException thrown when the conditions indicated * by the {@code Accept} header on the request cannot be met by the message converters */ @SuppressWarnings("unchecked") protected <T> void writeWithMessageConverters(T value, MethodParameter returnType, ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage) throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException { Object outputValue; Class<?> valueType; Type declaredType; if (value instanceof CharSequence) { // string 的返回值输出 outputValue = value.toString(); valueType = String.class; declaredType = String.class; } else { outputValue = value; valueType = getReturnValueType(outputValue, returnType); declaredType = getGenericType(returnType); } HttpServletRequest request = inputMessage.getServletRequest(); // 获取返回的 content-type 值 List<MediaType> requestedMediaTypes = getAcceptableMediaTypes(request); List<MediaType> producibleMediaTypes = getProducibleMediaTypes(request, valueType, declaredType); if (outputValue != null && producibleMediaTypes.isEmpty()) { throw new IllegalArgumentException("No converter found for return value of type: " + valueType); } Set<MediaType> compatibleMediaTypes = new LinkedHashSet<MediaType>(); for (MediaType requestedType : requestedMediaTypes) { for (MediaType producibleType : producibleMediaTypes) { if (requestedType.isCompatibleWith(producibleType)) { compatibleMediaTypes.add(getMostSpecificMediaType(requestedType, producibleType)); } } } if (compatibleMediaTypes.isEmpty()) { if (outputValue != null) { throw new HttpMediaTypeNotAcceptableException(producibleMediaTypes); } return; } List<MediaType> mediaTypes = new ArrayList<MediaType>(compatibleMediaTypes); MediaType.sortBySpecificityAndQuality(mediaTypes); // 确定输出的类型 MediaType selectedMediaType = null; for (MediaType mediaType : mediaTypes) { if (mediaType.isConcrete()) { selectedMediaType = mediaType; break; } else if (mediaType.equals(MediaType.ALL) || mediaType.equals(MEDIA_TYPE_APPLICATION)) { selectedMediaType = MediaType.APPLICATION_OCTET_STREAM; break; } } if (selectedMediaType != null) { selectedMediaType = selectedMediaType.removeQualityValue(); // 使用 messageConverter 进行返回值转换 // org.springframework.http.converter.ByteArrayHttpMessageConverter // org.springframework.http.converter.StringHttpMessageConverter // org.springframework.http.converter.ResourceHttpMessageConverter // org.springframework.http.converter.xml.SourceHttpMessageConverter // org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter // org.springframework.http.converter.xml.Jaxb2RootElementHttpMessageConverter // org.springframework.http.converter.ByteArrayHttpMessageConverter // org.springframework.http.converter.StringHttpMessageConverter // org.springframework.http.converter.ResourceHttpMessageConverter // org.springframework.http.converter.xml.SourceHttpMessageConverter // org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter // org.springframework.http.converter.xml.Jaxb2RootElementHttpMessageConverter for (HttpMessageConverter<?> messageConverter : this.messageConverters) { if (messageConverter instanceof GenericHttpMessageConverter) { if (((GenericHttpMessageConverter) messageConverter).canWrite( declaredType, valueType, selectedMediaType)) { outputValue = (T) getAdvice().beforeBodyWrite(outputValue, returnType, selectedMediaType, (Class<? extends HttpMessageConverter<?>>) messageConverter.getClass(), inputMessage, outputMessage); if (outputValue != null) { addContentDispositionHeader(inputMessage, outputMessage); ((GenericHttpMessageConverter) messageConverter).write( outputValue, declaredType, selectedMediaType, outputMessage); if (logger.isDebugEnabled()) { logger.debug("Written [" + outputValue + "] as "" + selectedMediaType + "" using [" + messageConverter + "]"); } } return; } } else if (messageConverter.canWrite(valueType, selectedMediaType)) { // 输出值 outputValue = (T) getAdvice().beforeBodyWrite(outputValue, returnType, selectedMediaType, (Class<? extends HttpMessageConverter<?>>) messageConverter.getClass(), inputMessage, outputMessage); if (outputValue != null) { addContentDispositionHeader(inputMessage, outputMessage); // write ((HttpMessageConverter) messageConverter).write(outputValue, selectedMediaType, outputMessage); if (logger.isDebugEnabled()) { logger.debug("Written [" + outputValue + "] as "" + selectedMediaType + "" using [" + messageConverter + "]"); } } return; } } } if (outputValue != null) { throw new HttpMediaTypeNotAcceptableException(this.allSupportedMediaTypes); } }
// 消息转换器
// org.springframework.http.converter.StringHttpMessageConverter
// org.springframework.http.converter.AbstractHttpMessageConverter
// org.springframework.http.converter.StringHttpMessageConverter // org.springframework.http.converter.AbstractHttpMessageConverter /** * This implementation sets the default headers by calling {@link #addDefaultHeaders}, * and then calls {@link #writeInternal}. */ @Override public final void write(final T t, MediaType contentType, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException { final HttpHeaders headers = outputMessage.getHeaders(); addDefaultHeaders(headers, t, contentType); if (outputMessage instanceof StreamingHttpOutputMessage) { StreamingHttpOutputMessage streamingOutputMessage = (StreamingHttpOutputMessage) outputMessage; streamingOutputMessage.setBody(new StreamingHttpOutputMessage.Body() { @Override public void writeTo(final OutputStream outputStream) throws IOException { writeInternal(t, new HttpOutputMessage() { @Override public OutputStream getBody() throws IOException { return outputStream; } @Override public HttpHeaders getHeaders() { return headers; } }); } }); } else { // write writeInternal(t, outputMessage); // 再次 flush() outputMessage.getBody().flush(); } } // StringHttpMessageConverter @Override protected void writeInternal(String str, HttpOutputMessage outputMessage) throws IOException { if (this.writeAcceptCharset) { outputMessage.getHeaders().setAcceptCharset(getAcceptedCharsets()); } Charset charset = getContentTypeCharset(outputMessage.getHeaders().getContentType()); StreamUtils.copy(str, charset, outputMessage.getBody()); } // org.springframework.util.StreamUtils.copy() // 像socket中写入返回值，即向浏览器一类请求客户端输出返回值，到此，客户端得到响应 /** * Copy the contents of the given String to the given output OutputStream. * Leaves the stream open when done. * @param in the String to copy from * @param charset the Charset * @param out the OutputStream to copy to * @throws IOException in case of I/O errors */ public static void copy(String in, Charset charset, OutputStream out) throws IOException { Assert.notNull(in, "No input String specified"); Assert.notNull(charset, "No charset specified"); Assert.notNull(out, "No OutputStream specified"); Writer writer = new OutputStreamWriter(out, charset); writer.write(in); writer.flush(); }
// return getModelAndView(mavContainer, modelFactory, webRequest);
// RequestMappingHandlerAdapter
// return getModelAndView(mavContainer, modelFactory, webRequest); // RequestMappingHandlerAdapter private ModelAndView getModelAndView(ModelAndViewContainer mavContainer, ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception { // 如果已经处理完成，返回null modelFactory.updateModel(webRequest, mavContainer); if (mavContainer.isRequestHandled()) { return null; } // 否则处理 mv ModelMap model = mavContainer.getModel(); ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model, mavContainer.getStatus()); if (!mavContainer.isViewReference()) { mav.setView((View) mavContainer.getView()); } if (model instanceof RedirectAttributes) { Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes(); HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class); RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes); } return mav; }
// prepareResponse(response);
// RequestMappingHandlerAdapter
/** * Prepare the given response according to the settings of this generator. * Applies the number of cache seconds specified for this generator. * @param response current HTTP response * @since 4.2 */ protected final void prepareResponse(HttpServletResponse response) { if (this.cacheControl != null) { applyCacheControl(response, this.cacheControl); } else { applyCacheSeconds(response, this.cacheSeconds); } if (servlet3Present && this.varyByRequestHeaders != null) { for (String value : getVaryRequestHeadersToAdd(response)) { response.addHeader("Vary", value); } } }
// mappedHandler.applyPostHandle(processedRequest, response, mv);
// org.springframework.web.servlet.HandlerExecutionChain.applyPostHandle(), 调用 interceptor.postHandle()
// org.springframework.web.servlet.HandlerExecutionChain.applyPostHandle(), 调用 interceptor.postHandle() /** * Apply postHandle methods of registered interceptors. */ 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); } } }
// processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
/** * Handle the result of handler selection and handler invocation, which is * either a ModelAndView or an Exception to be resolved to a ModelAndView. */ private void processDispatchResult(HttpServletRequest request, HttpServletResponse response, HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception { boolean errorView = false; // 发生异常，使用 errorView 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.isDebugEnabled()) { logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() + "': assuming HandlerAdapter completed request handling"); } } if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) { // Concurrent handling started during a forward return; } if (mappedHandler != null) { // 最后再一个触发器钩子，触发 interceptor.afterCompletion() mappedHandler.triggerAfterCompletion(request, response, null); } } /** * Trigger afterCompletion callbacks on the mapped HandlerInterceptors. * Will just invoke afterCompletion for all interceptors whose preHandle invocation * has successfully completed and returned true. */ 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); } } } }
// 依次返回 doDispatch()，清理环境
// 返回 FrameworkServlet.doService()
// FrameworkServlet finally中还会触发 requestAttributes.requestCompleted();
// org.springframework.web.context.request.ServletRequestAttributes.requestCompleted() /** * Signal that the request has been completed. * <p>Executes all request destruction callbacks and updates the * session attributes that have been accessed during request processing. */ public void requestCompleted() { executeRequestDestructionCallbacks(); updateAccessedSessionAttributes(); this.requestActive = false; } /** * Execute all callbacks that have been registered for execution * after request completion. */ private void executeRequestDestructionCallbacks() { synchronized (this.requestDestructionCallbacks) { for (Runnable runnable : this.requestDestructionCallbacks.values()) { // 同步调用 DestructionCallbacks.run() runnable.run(); } this.requestDestructionCallbacks.clear(); } } /** * Update all accessed session attributes through {@code session.setAttribute} * calls, explicitly indicating to the container that they might have been modified. */ @Override protected void updateAccessedSessionAttributes() { if (!this.sessionAttributesToUpdate.isEmpty()) { // Update all affected session attributes. HttpSession session = getSession(false); if (session != null) { try { for (Map.Entry<String, Object> entry : this.sessionAttributesToUpdate.entrySet()) { String name = entry.getKey(); Object newValue = entry.getValue(); Object oldValue = session.getAttribute(name); if (oldValue == newValue && !isImmutableSessionAttribute(name, newValue)) { session.setAttribute(name, newValue); } } } catch (IllegalStateException ex) { // Session invalidated - shouldn't usually happen. } } this.sessionAttributesToUpdate.clear(); } } // 最后 publishRequestHandledEvent(request, response, startTime, failureCause); // FrameworkServlet private void publishRequestHandledEvent( HttpServletRequest request, HttpServletResponse response, long startTime, Throwable failureCause) { if (this.publishEvents) { // Whether or not we succeeded, publish an event. long processingTime = System.currentTimeMillis() - startTime; int statusCode = (responseGetStatusAvailable ? response.getStatus() : -1); // 发布 event 到 spring, 使感兴趣的监听者进行相应处理 this.webApplicationContext.publishEvent( new ServletRequestHandledEvent(this, request.getRequestURI(), request.getRemoteAddr(), request.getMethod(), getServletConfig().getServletName(), WebUtils.getSessionId(request), getUsernameForRequest(request), processingTime, failureCause, statusCode)); } }
总结几个技术要点：
1. filterchain 责任链模式的使用；
2. 工厂模式的使用；
3. 拦截器监听；
4. 各功能组件化，职责分明；
5. 模板方法模式使用；
6. mvc；
7. 适配器模式应用；
8. 观察者模式应用；