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Spring 源码解析 -- SpringWeb 请求映射 Map 初始化

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发布于: 3 小时前

简介

在上篇文章中,大致解析了 Spring 如何将请求路径与处理方法进行映射,但映射相关的初始化对于我们来说还是一团迷雾


本篇文章就来探索下,请求路径和处理方法的映射,是如何进行初始化的

概览

基于上篇文章:Spring 源码解析 -- SpringWeb请求映射解析


本篇文章本来想早点写完,但一直卡着,没有找到想要的切入点,还好在周四左右定位到了相关的关键代码,初步探索到相关初始化的代码过程


接下来就展示这段时间的定位和解析过程,下面是自己这段时间探索历程:


  • 想定位 handlerMappings 的初始化,但没有定位请求 URL 和处理方法相关初始化的东西

  • 回过来头来看 handlerMappings ,看其有哪些东西,发现这个 Map 中并没有自定义的 HelloWorld

  • 意识到关键的 RequestMappingHandlerMapping,跟踪发送只有在这个类型才成功匹配

  • 回顾上篇的请求映射解析,在 RequestMappingHandlerMapping 细致初始化相关的代码

  • 成功找到相关的路径和处理方法初始化的关键代码


接下来详细看下:

源码解析

初步探索初始化:误入歧途

在类: DispatcherServlet.java 中,我们定位到 mappedHandler 获取的关键代码


@Nullableprotected 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;}
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它就是遍历了: handlerMappings ,于是去跟踪了 handlerMappings 初始化过程


结果失败而归,没有找到自己想要的东西,并没有发现自定义类: HelloWorld 的相关东西


这块有很多的代码,里面也有很多的东西,但在这里就不展示出来了,感兴趣的老哥可自行探索

回顾请求映射查找匹配:幡然醒悟

探索 handlerMappings 无果,于是回到上面那段遍历处理


经过调试 handlerMappings 基本是固定的,包含下面的类:


  • this.handlerMappings

  • RequestMappingHandlerMapping

  • BeanNameUrlHandlerMapping

  • RouterFunctionMapping

  • SimpleUrlHandlerMapping

  • WelcomePageHandlerMapping


而匹配的成功的是: RequestMappingHandlerMapping ,其返回了我们想要的处理方法 HelloWorld


调试中很疑惑为啥初期要初始化这几个了,并且再套了一层请求匹配,目前掌握的知识还不足于破解,只能后面再探索了


于是开始梳理 RequestMappingHandlerMapping 的请求匹配,在下面的一段关键代码匹配成功了:


    # AbstractHandlerMethodMapping.java    @Nullable  protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {    List<Match> matches = new ArrayList<>();        // 在这里拿到了匹配结果    List<T> directPathMatches = this.mappingRegistry.getMappingsByDirectPath(lookupPath);    if (directPathMatches != null) {      addMatchingMappings(directPathMatches, matches, request);    }    if (matches.isEmpty()) {      addMatchingMappings(this.mappingRegistry.getRegistrations().keySet(), matches, request);    }    .......  }
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在上面的代码中就匹配成功了,其中匹配的方法很简单粗暴:


    # AbstractHandlerMethodMapping.java -- MappingRegistry    @Nullable  public List<T> getMappingsByDirectPath(String urlPath) {    return this.pathLookup.get(urlPath);  }
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于是关键点到了 this.mappingRegistry 的初始化,找到初始化的代码,打上断点


期间以为是在类:AbstractHandlerMethodMapping 中进行的初始的,在下面的函数打上了断点:


    # AbstractHandlerMethodMapping.java    public 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); }
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但一直进不去,于是直接在其定义的内部类中: MappingRegistry 中进行寻找,并成功定位到想要的关键代码

请求映射关键代码定位:柳暗花明

阅读类: MappingRegistry 的相关代码,发现下面的方法和可以,我们直接打上断点,重启程序:


发现了前面的: this.pathLookup 的相关添加操作


    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) { // 这段代码是关键 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(); } }
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应用重启后,果然顺利来到我们打上的断点处,通过分析调用栈,我们确实找到了请求映射的关键代码


我们将调用栈从下网上分析查看:

应用启动相关

开始就是熟悉 Spring 启动相关,这些代码相信大家尝试阅读源码的时候读过很多遍了


跟踪发现在: DefaultListableBeanFactory.class 的 preInstantiateSingletons 方法中个,一大段嵌套循环,心想这段代码目前能优化吗?


    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); // 从下面这个进入 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(); // 从这里进入 this.finishBeanFactoryInitialization(beanFactory); this.finishRefresh(); } catch (BeansException var10) { } finally { ...... } ...... } }
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RequestMappingHandlerMapping 相关初始化

继续跟踪下面的,看到了属性的 CreateBean 和 afterPropertiesSet


    # AbstractAutowireCapableBeanFactory.class    protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) throws BeanCreationException {        ......        try {            // 这里初始化了 RequestMappingHandlerMapping            beanInstance = 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.class protected 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 { // 这里进入请求映射的相关操作 ((InitializingBean)bean).afterPropertiesSet(); } } ...... }
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请求映射初始化

继续跟踪下去,看看了循环遍历 Controllers 相关的代码(还有很多细节没搞清,后面再继续了,先梳理主线)


    # AbstractHandlerMethodMapping.java    @Override  public void afterPropertiesSet() {        // 初始化请求映射    initHandlerMethods();  }
protected void initHandlerMethods() { // 遍历所有的自定义的Controllers,后面自己又定义了一个Controllers for (String beanName : getCandidateBeanNames()) { if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) { // 在这里看到了我们定义的HelloWorld processCandidateBean(beanName); } } handlerMethodsInitialized(getHandlerMethods()); }
protected String[] getCandidateBeanNames() { return (this.detectHandlerMethodsInAncestorContexts ? BeanFactoryUtils.beanNamesForTypeIncludingAncestors(obtainApplicationContext(), Object.class) : obtainApplicationContext().getBeanNamesForType(Object.class)); }
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继续跟踪下去,看到了下面的获取类中具体请求路径相关的代码,并且到了具体的初始化请求映射的代码


    # AbstractHandlerMethodMapping.java    protected 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) { // 处理得到所有的Controllers method Class<?> 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); // 注册 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(); } }
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总结

经过一段时间的探索的整理,我们终于得到了大致的请求路径映射初始化的代码


  • 1.应用启动时,初始化:RequestMappingHandlerMapping

  • 2.RequestMappingHandlerMapping 中请求路径初始化


经过调试,我们还发现虽然 RequestMappingHandlerMapping 是一开始就初始化了,但加载到 handlerMappings 是第一次请求的时候才加载进去的


本篇虽然得到了大致的请求路径初始化的代码,但其中有很多细节是值得探索的,比如 Bean 中 Method 的处理


之前自己写过一些 DI 和 Web 相关的 Demo,停在了 Servlet,卡在了请求映射初始化和匹配,这个给了我一些思路,后面详细看看这块代码,完善下之前的 Demo

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发布于: 3 小时前阅读数: 2
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Spring源码解析 -- SpringWeb请求映射Map初始化