SpringMVC源码解析（二）

系统管理员 2024-04-18 20:40 84阅读 0赞

> 注意，读完本篇文章需要很长很长时间

在上篇文章[SpringMVC源码解析（一）][SpringMVC]中，我们搭建了一个SpringBoot的启动demo，分析了SpringBoot中SpringMVC的自动配置原理以及`DispatcherServlet`的初始化流程。本篇文章就分析一次请求在SpringMVC中的处理流程

在日常开发中，我们最常用的请求方式大概就是Get和Post了，Tomcat或者Jetty等web服务器在接受到请求后会调用到`DispatcherServlet`对应的方法

可以看到其实最终都是调用的同一个方法

<table> 
 <tbody> 
 <tr> 
 <td><pre>1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 </pre></td> 
 <td><pre>protected final void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 //记录开始时间 long startTime = System.currentTimeMillis(); Throwable failureCause = null; //记录当前线程的信息 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 {
 //核心处理，往下看 doService(request, response); } catch (ServletException | IOException ex) {
 failureCause = ex; throw ex; } catch (Throwable ex) {
 failureCause = ex; throw new NestedServletException("Request processing failed", ex); } finally {
 //清除线程绑定信息 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"); } } } //发送事件通知 publishRequestHandledEvent(request, response, startTime, failureCause); } } 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&lt;String, Object&gt; attributesSnapshot = null; if (WebUtils.isIncludeRequest(request)) {
 attributesSnapshot = new HashMap&lt;&gt;(); Enumeration&lt;?&gt; 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); } } } } </pre></td> 
 </tr> 
 </tbody> 
</table>

可以看到上方的大段代码都是做的一些准备工作，具体的逻辑接着往下看吧，这个核心流程都在下面这个方法里了

##### 1. 获取handler #####

###### 1. 获取具体的handler ######

这里以`AbstractUrlHandlerMapping`为例解读一下，顾明思议，这个类是根据请求url获取响应的handler的

<table> 
 <tbody> 
 <tr> 
 <td><pre>1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 </pre></td> 
 <td><pre>protected Object getHandlerInternal(HttpServletRequest request) throws Exception {
 //截取url String lookupPath = getUrlPathHelper().getLookupPathForRequest(request); //根据url寻找handler Object handler = lookupHandler(lookupPath, request); if (handler == null) {
 // 如果请求路径为/则使用RootHandler Object rawHandler = null; if ("/".equals(lookupPath)) {
 rawHandler = getRootHandler(); } if (rawHandler == null) {
 //使用默认 rawHandler = getDefaultHandler(); } if (rawHandler != null) {
 // 根据beanName尝试获取Handler if (rawHandler instanceof String) {
 String handlerName = (String) rawHandler; rawHandler = obtainApplicationContext().getBean(handlerName); }//校验 validateHandler(rawHandler, request); handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null); } } if (handler != null &amp;&amp; logger.isDebugEnabled()) {
 logger.debug("Mapping [" + lookupPath + "] to " + handler); } else if (handler == null &amp;&amp; logger.isTraceEnabled()) {
 logger.trace("No handler mapping found for [" + lookupPath + "]"); } return handler; } protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {
 // 直接根据url匹配 Object handler = this.handlerMap.get(urlPath); if (handler != null) {
 // Bean name or resolved handler? if (handler instanceof String) {
 String handlerName = (String) handler; handler = obtainApplicationContext().getBean(handlerName); } validateHandler(handler, request); //封装执行链 return buildPathExposingHandler(handler, urlPath, urlPath, null); } // 正则匹配 List&lt;String&gt; matchingPatterns = new ArrayList&lt;&gt;(); for (String registeredPattern : this.handlerMap.keySet()) {
 if (getPathMatcher().match(registeredPattern, urlPath)) {
 matchingPatterns.add(registeredPattern); } else if (useTrailingSlashMatch()) {
 if (!registeredPattern.endsWith("/") &amp;&amp; getPathMatcher().match(registeredPattern + "/", urlPath)) {
 matchingPatterns.add(registeredPattern +"/"); } } } String bestMatch = null; Comparator&lt;String&gt; patternComparator = getPathMatcher().getPatternComparator(urlPath); if (!matchingPatterns.isEmpty()) {
 matchingPatterns.sort(patternComparator); if (logger.isDebugEnabled()) {
 logger.debug("Matching patterns for request [" + urlPath + "] are " + matchingPatterns); } bestMatch = matchingPatterns.get(0); } if (bestMatch != null) {
 handler = this.handlerMap.get(bestMatch); if (handler == null) {
 if (bestMatch.endsWith("/")) {
 handler = this.handlerMap.get(bestMatch.substring(0, bestMatch.length() - 1)); } if (handler == null) {
 throw new IllegalStateException( "Could not find handler for best pattern match [" + bestMatch + "]"); } } // Bean name or resolved handler? if (handler instanceof String) {
 String handlerName = (String) handler; handler = obtainApplicationContext().getBean(handlerName); } validateHandler(handler, request); String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestMatch, urlPath); // There might be multiple 'best patterns', let's make sure we have the correct URI template variables // for all of them Map&lt;String, String&gt; uriTemplateVariables = new LinkedHashMap&lt;&gt;(); for (String matchingPattern : matchingPatterns) {
 if (patternComparator.compare(bestMatch, matchingPattern) == 0) {
 Map&lt;String, String&gt; vars = getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath); Map&lt;String, String&gt; decodedVars = getUrlPathHelper().decodePathVariables(request, vars); uriTemplateVariables.putAll(decodedVars); } } if (logger.isDebugEnabled()) {
 logger.debug("URI Template variables for request [" + urlPath + "] are " + uriTemplateVariables); } return buildPathExposingHandler(handler, bestMatch, pathWithinMapping, uriTemplateVariables); } // No handler found... return null; } </pre></td> 
 </tr> 
 </tbody> 
</table>

###### 2. 封装执行链 ######

当获取到相应的handler后，查看是否存在拦截器，如果存在的话则加入执行链中

##### 2. 获取handlerAdpter #####

根据handler获取匹配的handlerAdpter

##### 3. 执行请求 #####

##### 4.处理返回结果 #####

页面跳转的逻辑

###### 解析视图名称 ######

###### 页面跳转 ######

具体的跳转逻辑是根据当前使用的渲染引擎决定的，比如html、jsp、Thymeleaf等，这里简单 列举一个Thymeleaf的逻辑吧

<table> 
 <tbody> 
 <tr> 
 <td><pre>1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 </pre></td> 
 <td><pre>public void render(Map&lt;String, ?&gt; model, HttpServletRequest request, HttpServletResponse response) throws Exception {
 this.renderFragment(this.markupSelectors, model, request, response); } protected void renderFragment(Set&lt;String&gt; markupSelectorsToRender, Map&lt;String, ?&gt; model, HttpServletRequest request, HttpServletResponse response) throws Exception {
 ServletContext servletContext = this.getServletContext(); String viewTemplateName = this.getTemplateName(); ISpringTemplateEngine viewTemplateEngine = this.getTemplateEngine(); if (viewTemplateName == null) {
 throw new IllegalArgumentException("Property 'templateName' is required"); } else if (this.getLocale() == null) {
 throw new IllegalArgumentException("Property 'locale' is required"); } else if (viewTemplateEngine == null) {
 throw new IllegalArgumentException("Property 'templateEngine' is required"); } else {
 Map&lt;String, Object&gt; mergedModel = new HashMap(30); Map&lt;String, Object&gt; templateStaticVariables = this.getStaticVariables(); if (templateStaticVariables != null) {
 mergedModel.putAll(templateStaticVariables); } if (pathVariablesSelector != null) {
 Map&lt;String, Object&gt; pathVars = (Map)request.getAttribute(pathVariablesSelector); if (pathVars != null) {
 mergedModel.putAll(pathVars); } } if (model != null) {
 mergedModel.putAll(model); } ApplicationContext applicationContext = this.getApplicationContext(); RequestContext requestContext = new RequestContext(request, response, this.getServletContext(), mergedModel); SpringWebMvcThymeleafRequestContext thymeleafRequestContext = new SpringWebMvcThymeleafRequestContext(requestContext, request); addRequestContextAsVariable(mergedModel, "springRequestContext", requestContext); addRequestContextAsVariable(mergedModel, "springMacroRequestContext", requestContext); mergedModel.put("thymeleafRequestContext", thymeleafRequestContext); ConversionService conversionService = (ConversionService)request.getAttribute(ConversionService.class.getName()); ThymeleafEvaluationContext evaluationContext = new ThymeleafEvaluationContext(applicationContext, conversionService); mergedModel.put("thymeleaf::EvaluationContext", evaluationContext); IEngineConfiguration configuration = viewTemplateEngine.getConfiguration(); WebExpressionContext context = new WebExpressionContext(configuration, request, response, servletContext, this.getLocale(), mergedModel); String templateName; Set markupSelectors; if (!viewTemplateName.contains("::")) {
 templateName = viewTemplateName; markupSelectors = null; } else {
 IStandardExpressionParser parser = StandardExpressions.getExpressionParser(configuration); FragmentExpression fragmentExpression; try {
 fragmentExpression = (FragmentExpression)parser.parseExpression(context, "~{" + viewTemplateName + "}"); } catch (TemplateProcessingException var24) {
 throw new IllegalArgumentException("Invalid template name specification: '" + viewTemplateName + "'"); } ExecutedFragmentExpression fragment = FragmentExpression.createExecutedFragmentExpression(context, fragmentExpression); templateName = FragmentExpression.resolveTemplateName(fragment); markupSelectors = FragmentExpression.resolveFragments(fragment); Map&lt;String, Object&gt; nameFragmentParameters = fragment.getFragmentParameters(); if (nameFragmentParameters != null) {
 if (fragment.hasSyntheticParameters()) {
 throw new IllegalArgumentException("Parameters in a view specification must be named (non-synthetic): '" + viewTemplateName + "'"); } context.setVariables(nameFragmentParameters); } } String templateContentType = this.getContentType(); Locale templateLocale = this.getLocale(); String templateCharacterEncoding = this.getCharacterEncoding(); Set processMarkupSelectors; if (markupSelectors != null &amp;&amp; markupSelectors.size() &gt; 0) {
 if (markupSelectorsToRender != null &amp;&amp; markupSelectorsToRender.size() &gt; 0) {
 throw new IllegalArgumentException("A markup selector has been specified (" + Arrays.asList(markupSelectors) + ") for a view that was already being executed as a fragment (" + Arrays.asList(markupSelectorsToRender) + "). Only one fragment selection is allowed."); } processMarkupSelectors = markupSelectors; } else if (markupSelectorsToRender != null &amp;&amp; markupSelectorsToRender.size() &gt; 0) {
 processMarkupSelectors = markupSelectorsToRender; } else {
 processMarkupSelectors = null; } response.setLocale(templateLocale); if (!this.getForceContentType()) {
 String computedContentType = SpringContentTypeUtils.computeViewContentType(request, templateContentType != null ? templateContentType : "text/html;charset=ISO-8859-1", templateCharacterEncoding != null ? Charset.forName(templateCharacterEncoding) : null); response.setContentType(computedContentType); } else {
 if (templateContentType != null) {
 response.setContentType(templateContentType); } else {
 response.setContentType("text/html;charset=ISO-8859-1"); } if (templateCharacterEncoding != null) {
 response.setCharacterEncoding(templateCharacterEncoding); } } viewTemplateEngine.process(templateName, processMarkupSelectors, context, response.getWriter()); } }</pre></td> 
 </tr> 
 </tbody> 
</table>

![640?wx\_fmt=png][640_wx_fmt_png]

[SpringMVC]: https://mp.weixin.qq.com/s?__biz=MzU5MDgzOTYzMw==&mid=2247484627&idx=1&sn=a31b91e54e040ac9eac6eb5fd0dff0d7&scene=21#wechat_redirect
[640_wx_fmt_png]: https://ss.csdn.net/p?https://mmbiz.qpic.cn/mmbiz_png/yjcnia03icoX22ocZS2fDO6ScdrPbpfAY9icnefzNWjropeibNDjufbsveC0CTMsN8VicLgUI8mBxR8GYCKSIQvphbQ/640?wx_fmt=png