importjava，Spring源碼解析 -- SpringWeb請求映射Map初始化

2023-10-12 阅读 32 评论 0

摘要：簡介在上篇文章中，大致解析了Spring如何將請求路徑與處理方法進行映射，但映射相關的初始化對于我們來說還是一團迷霧本篇文章就來探索下，請求路徑和處理方法的映射，是如何進行初始化的概覽基于上篇文章：Spring 源碼解析 – SpringWeb請

簡介

在上篇文章中，大致解析了Spring如何將請求路徑與處理方法進行映射，但映射相關的初始化對于我們來說還是一團迷霧

本篇文章就來探索下，請求路徑和處理方法的映射，是如何進行初始化的

概覽

基于上篇文章：Spring 源碼解析 – SpringWeb請求映射解析

本篇文章本來想早點寫完，但一直卡著，沒有找到想要的切入點，還好在周四左右定位到了相關的關鍵代碼，初步探索到相關初始化的代碼過程

importjava、接下來就展示這段時間的定位和解析過程，下面是自己這段時間探索歷程：

想定位 handlerMappings 的初始化，但沒有定位請求URL和處理方法相關初始化的東西
回過來頭來看 handlerMappings ，看其有哪些東西,發現這個Map中并沒有自定義的HelloWorld
意識到關鍵的 RequestMappingHandlerMapping，跟蹤發送只有在這個類型才成功匹配
回顧上篇的請求映射解析，在 RequestMappingHandlerMapping 細致初始化相關的代碼
成功找到相關的路徑和處理方法初始化的關鍵代碼

接下來詳細看下：

源碼解析

初步探索初始化：誤入歧途

在類： DispatcherServlet.java 中，我們定位到 mappedHandler 獲取的關鍵代碼

@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {if (this.handlerMappings != null) {for (HandlerMapping mapping : this.handlerMappings) {HandlerExecutionChain handler = mapping.getHandler(request);if (handler != null) {return handler;}}}return null;
}

它就是遍歷了： handlerMappings ,于是去跟蹤了 handlerMappings 初始化過程

結果失敗而歸，沒有找到自己想要的東西，并沒有發現自定義類： HelloWorld 的相關東西

import java.lang？這塊有很多的代碼，里面也有很多的東西，但在這里就不展示出來了，感興趣的老哥可自行探索

回顧請求映射查找匹配：幡然醒悟

探索 handlerMappings 無果，于是回到上面那段遍歷處理

經過調試 handlerMappings 基本是固定的，包含下面的類：

this.handlerMappings
- RequestMappingHandlerMapping
- BeanNameUrlHandlerMapping
- RouterFunctionMapping
- SimpleUrlHandlerMapping
- WelcomePageHandlerMapping

而匹配的成功的是： RequestMappingHandlerMapping ，其返回了我們想要的處理方法 HelloWorld

調試中很疑惑為啥初期要初始化這幾個了，并且再套了一層請求匹配，目前掌握的知識還不足于破解，只能后面再探索了

java bean轉map？于是開始梳理 RequestMappingHandlerMapping 的請求匹配，在下面的一段關鍵代碼匹配成功了：

    # AbstractHandlerMethodMapping.java@Nullableprotected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {List<Match> matches = new ArrayList<>();// 在這里拿到了匹配結果List<T> directPathMatches = this.mappingRegistry.getMappingsByDirectPath(lookupPath);if (directPathMatches != null) {addMatchingMappings(directPathMatches, matches, request);}if (matches.isEmpty()) {addMatchingMappings(this.mappingRegistry.getRegistrations().keySet(), matches, request);}.......}

在上面的代碼中就匹配成功了，其中匹配的方法很簡單粗暴：

    # AbstractHandlerMethodMapping.java -- MappingRegistry@Nullablepublic List<T> getMappingsByDirectPath(String urlPath) {return this.pathLookup.get(urlPath);}

于是關鍵點到了 this.mappingRegistry 的初始化，找到初始化的代碼，打上斷點

期間以為是在類：AbstractHandlerMethodMapping 中進行的初始的，在下面的函數打上了斷點：

    # AbstractHandlerMethodMapping.javapublic void setPatternParser(PathPatternParser patternParser) {Assert.state(this.mappingRegistry.getRegistrations().isEmpty(),"PathPatternParser must be set before the initialization of " +"request mappings through InitializingBean#afterPropertiesSet.");super.setPatternParser(patternParser);}public void registerMapping(T mapping, Object handler, Method method) {if (logger.isTraceEnabled()) {logger.trace("Register \"" + mapping + "\" to " + method.toGenericString());}this.mappingRegistry.register(mapping, handler, method);}

但一直進不去，于是直接在其定義的內部類中： MappingRegistry 中進行尋找，并成功定位到想要的關鍵代碼

請求映射關鍵代碼定位：柳暗花明

map轉bean對象。閱讀類： MappingRegistry 的相關代碼，發現下面的方法和可以，我們直接打上斷點，重啟程序：

發現了前面的: this.pathLookup 的相關添加操作

    public void register(T mapping, Object handler, Method method) {this.readWriteLock.writeLock().lock();try {HandlerMethod handlerMethod = createHandlerMethod(handler, method);validateMethodMapping(handlerMethod, mapping);Set<String> directPaths = AbstractHandlerMethodMapping.this.getDirectPaths(mapping);for (String path : directPaths) {// 這段代碼是關鍵this.pathLookup.add(path, mapping);}String name = null;if (getNamingStrategy() != null) {name = getNamingStrategy().getName(handlerMethod, mapping);addMappingName(name, handlerMethod);}CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);if (corsConfig != null) {corsConfig.validateAllowCredentials();this.corsLookup.put(handlerMethod, corsConfig);}this.registry.put(mapping,new MappingRegistration<>(mapping, handlerMethod, directPaths, name, corsConfig != null));}finally {this.readWriteLock.writeLock().unlock();}}

應用重啟后，果然順利來到我們打上的斷點處，通過分析調用棧，我們確實找到了請求映射的關鍵代碼

我們將調用棧從下網上分析查看：

應用啟動相關

開始就是熟悉Spring啟動相關，這些代碼相信大家嘗試閱讀源碼的時候讀過很多遍了

Springboot？跟蹤發現在： DefaultListableBeanFactory.class 的 preInstantiateSingletons 方法中個，一大段嵌套循環，心想這段代碼目前能優化嗎？

    public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {return (new SpringApplication(primarySources)).run(args);}public static void main(String[] args) throws Exception {run(new Class[0], args);}public ConfigurableApplicationContext run(String... args) {......try {......this.prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);// 從下面這個進入this.refreshContext(context);this.afterRefresh(context, applicationArguments);......} catch (Throwable var10) {......this.handleRunFailure(context, var10, listeners);throw new IllegalStateException(var10);}......}public void refresh() throws BeansException, IllegalStateException {synchronized(this.startupShutdownMonitor) {.......try {this.postProcessBeanFactory(beanFactory);StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");this.invokeBeanFactoryPostProcessors(beanFactory);this.registerBeanPostProcessors(beanFactory);beanPostProcess.end();this.initMessageSource();this.initApplicationEventMulticaster();this.onRefresh();this.registerListeners();// 從這里進入this.finishBeanFactoryInitialization(beanFactory);this.finishRefresh();} catch (BeansException var10) {} finally {......}......}}

RequestMappingHandlerMapping 相關初始化

繼續跟蹤下面的，看到了屬性的CreateBean和afterPropertiesSet

    # AbstractAutowireCapableBeanFactory.classprotected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationException {......try {// 這里初始化了 RequestMappingHandlerMappingbeanInstance = this.doCreateBean(beanName, mbdToUse, args);if (this.logger.isTraceEnabled()) {this.logger.trace("Finished creating instance of bean '" + beanName + "'");}return beanInstance;} catch (ImplicitlyAppearedSingletonException | BeanCreationException var7) {throw var7;} catch (Throwable var8) {throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", var8);}}# AbstractAutowireCapableBeanFactory.classprotected void invokeInitMethods(String beanName, Object bean, @Nullable RootBeanDefinition mbd) throws Throwable {boolean isInitializingBean = bean instanceof InitializingBean;if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {if (this.logger.isTraceEnabled()) {this.logger.trace("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");}if (System.getSecurityManager() != null) {try {AccessController.doPrivileged(() -> {((InitializingBean)bean).afterPropertiesSet();return null;}, this.getAccessControlContext());} catch (PrivilegedActionException var6) {throw var6.getException();}} else {// 這里進入請求映射的相關操作((InitializingBean)bean).afterPropertiesSet();}}......}

請求映射初始化

繼續跟蹤下去，看看了循環遍歷Controllers相關的代碼（還有很多細節沒搞清，后面再繼續了，先梳理主線）

    # AbstractHandlerMethodMapping.java@Overridepublic void afterPropertiesSet() {// 初始化請求映射initHandlerMethods();}protected void initHandlerMethods() {// 遍歷所有的自定義的Controllers，后面自己又定義了一個Controllersfor (String beanName : getCandidateBeanNames()) {if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {// 在這里看到了我們定義的HelloWorldprocessCandidateBean(beanName);}}handlerMethodsInitialized(getHandlerMethods());}protected String[] getCandidateBeanNames() {return (this.detectHandlerMethodsInAncestorContexts ?BeanFactoryUtils.beanNamesForTypeIncludingAncestors(obtainApplicationContext(), Object.class) :obtainApplicationContext().getBeanNamesForType(Object.class));}

繼續跟蹤下去，看到了下面的獲取類中具體請求路徑相關的代碼，并且到了具體的初始化請求映射的代碼

    # AbstractHandlerMethodMapping.javaprotected void processCandidateBean(String beanName) {Class<?> beanType = null;try {beanType = obtainApplicationContext().getType(beanName);}catch (Throwable ex) {// An unresolvable bean type, probably from a lazy bean - let's ignore it.if (logger.isTraceEnabled()) {logger.trace("Could not resolve type for bean '" + beanName + "'", ex);}}if (beanType != null && isHandler(beanType)) {// 得到Controller Bean后的入口detectHandlerMethods(beanName);}}protected void detectHandlerMethods(Object handler) {Class<?> handlerType = (handler instanceof String ?obtainApplicationContext().getType((String) handler) : handler.getClass());if (handlerType != null) {// 處理得到所有的Controllers methodClass<?> userType = ClassUtils.getUserClass(handlerType);Map<Method, T> methods = MethodIntrospector.selectMethods(userType,(MethodIntrospector.MetadataLookup<T>) method -> {try {return getMappingForMethod(method, userType);}catch (Throwable ex) {throw new IllegalStateException("Invalid mapping on handler class [" +userType.getName() + "]: " + method, ex);}});if (logger.isTraceEnabled()) {logger.trace(formatMappings(userType, methods));}else if (mappingsLogger.isDebugEnabled()) {mappingsLogger.debug(formatMappings(userType, methods));}methods.forEach((method, mapping) -> {Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);// 注冊registerHandlerMethod(handler, invocableMethod, mapping);});}}public void register(T mapping, Object handler, Method method) {this.readWriteLock.writeLock().lock();try {HandlerMethod handlerMethod = createHandlerMethod(handler, method);validateMethodMapping(handlerMethod, mapping);Set<String> directPaths = AbstractHandlerMethodMapping.this.getDirectPaths(mapping);for (String path : directPaths) {// 映射添加this.pathLookup.add(path, mapping);}}finally {this.readWriteLock.writeLock().unlock();}}