Spring mvc 从一个http请求分析DispatcherServlet的工作过程

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目标、调试 请求http://localhost:8080/coffee/helloworld

 <servlet>        <servlet-name>dispatcher</servlet-name>        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>        <init-param>            <param-name>contextConfigLocation</param-name>            <param-value>/WEB-INF/dispatcher-servlet.xml</param-value>        </init-param>        <load-on-startup>1</load-on-startup>    </servlet>    <servlet-mapping>        <servlet-name>dispatcher</servlet-name>        <url-pattern>/coffee</url-pattern>    </servlet-mapping>

url-pattern 拦截所有的/coffee开头的请求

@Controller@RequestMapping("coffee")public class HelloControler{@RequestMapping("helloworld")public @ResponseBody String helloWorld() {System.out.println("xxx");return "hello 222 world";}}

<pre style="font-family: 宋体; font-size: 12pt; background-color: rgb(255, 255, 255);"><pre name="code" class="java">/** * 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 */@Overrideprotected final void doGet(HttpServletRequest request, HttpServletResponse response)      throws ServletException, IOException {   processRequest(request, response);} 

 org.springframework.web.servlet.FrameworkServlet

/** * 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);//******* doService *********//}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) {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");}}}publishRequestHandledEvent(request, response, startTime, failureCause);}}

接着看一下 DispatcherServlet的方法

/** * Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch} * for the actual dispatching. */@Overrideprotected 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));}}}// 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());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);}}}}

然后看一下 最关键的方法

/** * 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 {processedRequest = checkMultipart(request);multipartRequestParsed = (processedRequest != request);// **********************************根据request查找mappedHandler 也就是一个Controller// Determine handler for the current request.mappedHandler = getHandler(processedRequest);if (mappedHandler == null || mappedHandler.getHandler() == 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 (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;}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 afterCompletionif (mappedHandler != null) {mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);}}else {// Clean up any resources used by a multipart request.if (multipartRequestParsed) {cleanupMultipart(processedRequest);}}}}

看一下Spring如何匹配url 然后查找对应的Controller

/** * 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 {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;}

private List<HandlerMapping> handlerMappings;

handlerMappings 是包含俩元素

BeanNameUrlHandlerMapping 
DefaultAnnotationHandlerMapping
package org.springframework.web.servlet.handler;
/** * 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 */@Overridepublic final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {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);}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;}

package org.springframework.web.servlet.handler;
/** * Look up a handler for the URL path of the given request. * @param request current HTTP request * @return the handler instance, or {@code null} if none found */@Overrideprotected Object getHandlerInternal(HttpServletRequest request) throws Exception {String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);//coffee/helloworld *** 往下看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;}

package org.springframework.web.util;
class UrlPathHelper
 public String getLookupPathForRequest(HttpServletRequest request) {        if(this.alwaysUseFullPath) {            return this.getPathWithinApplication(request);        } else {            String rest = this.getPathWithinServletMapping(request);//运行结果 --> ""            return !"".equals(rest)?rest:this.getPathWithinApplication(request);//执行getpathWithApplication 返回 /coffee/helloworld        }    }
上面的方法执行的是else
public String getPathWithinServletMapping(HttpServletRequest request) {        String pathWithinApp = this.getPathWithinApplication(request);//coffee/helloworld  ******往下看        String servletPath = this.getServletPath(request);<span style="font-family: 宋体;">//coffee/helloworld  </span><span style="font-family: 宋体;">******往下看</span>        String sanitizedPathWithinApp = this.getSanitizedPath(pathWithinApp);        String path;        if(servletPath.contains(sanitizedPathWithinApp)) {            path = this.getRemainingPath(sanitizedPathWithinApp, servletPath, false); //结果 ""        } else {            path = this.getRemainingPath(pathWithinApp, servletPath, false);        }        if(path != null) {            return path; // 返回 ""        } else {            String pathInfo = request.getPathInfo();            if(pathInfo != null) {                return pathInfo;            } else {                if(!this.urlDecode) {                    path = this.getRemainingPath(this.decodeInternal(request, pathWithinApp), servletPath, false);                    if(path != null) {                        return pathWithinApp;                    }                }                return servletPath;            }        }    }

public String getPathWithinApplication(HttpServletRequest request) {        String contextPath = this.getContextPath(request);// ""        String requestUri = this.getRequestUri(request);//coffee/helloworld        String path = this.getRemainingPath(requestUri, contextPath, true);//coffee/helloworld        return path != null?(StringUtils.hasText(path)?path:"/"):requestUri;//coffee/helloworld    }

 public String getContextPath(HttpServletRequest request) {        String contextPath = (String)request.getAttribute("javax.servlet.include.context_path");        if(contextPath == null) {            contextPath = request.getContextPath();        }        if("/".equals(contextPath)) {///*****注意一下这个方法如果            contextPath = "";        }        return this.decodeRequestString(request, contextPath);    }

public String getServletPath(HttpServletRequest request) {        String servletPath = (String)request.getAttribute("javax.servlet.include.servlet_path");        if(servletPath == null) {            servletPath = request.getServletPath();//*******/coffee/helloworld        }        if(servletPath.length() > 1 && servletPath.endsWith("/") && this.shouldRemoveTrailingServletPathSlash(request)) {            servletPath = servletPath.substring(0, servletPath.length() - 1);        }        return servletPath;    }


/** * Look up a handler instance for the given URL path. * <p>Supports direct matches, e.g. a registered "/test" matches "/test", * and various Ant-style pattern matches, e.g. a registered "/t*" matches * both "/test" and "/team". For details, see the AntPathMatcher class. * <p>Looks for the most exact pattern, where most exact is defined as * the longest path pattern. * @param urlPath URL the bean is mapped to * @param request current HTTP request (to expose the path within the mapping to) * @return the associated handler instance, or {@code null} if not found * @see #exposePathWithinMapping * @see org.springframework.util.AntPathMatcher */protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {// Direct match? *************************************下面一行代码是真正查询Controller的方法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 themMap<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;}