spring boot 加载web容器tomcat流程源码分析
小刘 2021-08-28 09:19:08 2021-08-28 137 0
spring boot 加载web容器tomcat流程源码分析
我本地的springboot版本是2.5.1，后面的分析都是基于这个版本
<parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.5.1</version> <relativePath/> <!-- lookup parent from repository --> </parent>我们通过在pom文件中引入
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency>来引入web容器，默认的web容器时tomcat。
本文章主要描述spring boot加载web容器 tomcat的部分，为了避免文章知识点过于分散，其他相关的如bean的加载，tomcat内部流程等不做深入讨论。
1、在springboot web工程中，全局上下文是AnnotationConfigServletWebApplicationContext
下面的部分，我们具体来看下
首先，我们的入口代码一般都是这样写的
public static void main(String[] args) { SpringApplication.run(BootargsApplication.class,args); }跳转到run方法里面，依次会调用下面两个方法
public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) { return run(new Class<?>[] { primarySource }, args); }public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) { return new SpringApplication(primarySources).run(args);}首先会创建SpringApplication实例对象，跳转到SpringApplication的构造方法去看看，依次会调用如下方法
public SpringApplication(Class<?>... primarySources) { this(null, primarySources); }@SuppressWarnings({ "unchecked", "rawtypes" })public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) { ...... //本次不相关的代码全部省略掉，只保留相关代码 //这里的 this.webApplicationType=WebApplicationType.SERVLET， 我们来分析下这个代码的具体的执行赋值 this.webApplicationType = WebApplicationType.deduceFromClasspath(); ......}继续跳转到WebApplicationType.deduceFromClasspath()去看看
//这个方法主要是在当前类路径下查找指定的class类是否存在，返回对饮枚举类型 static WebApplicationType deduceFromClasspath() { // WEBMVC_INDICATOR_CLASS = "org.springframework.web.servlet.DispatcherServlet"; //我们通过pom文件引入spring-boot-starter-web，会简介引入spring-webmvc,上面这个类就在这个webmvc中，所以不会进入这个if分支 if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null) && !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null) && !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) { return WebApplicationType.REACTIVE; } //SERVLET_INDICATOR_CLASSES = { "javax.servlet.Servlet", "org.springframework.web.context.ConfigurableWebApplicationContext" } //javax.servlet.Servlet这个类存在于tomcat-embed-core中 //org.springframework.web.context.ConfigurableWebApplicationContext这个类存在于spring-web中 //这两个jar都是由spring-boot-starter-web间接引入的，所以也不会走这个分支 for (String className : SERVLET_INDICATOR_CLASSES) { if (!ClassUtils.isPresent(className, null)) { return WebApplicationType.NONE; } } //所以会从这里返回 return WebApplicationType.SERVLET; }下面看下jar包的引入
回到new SpringApplication(primarySources).run(args)的调用来看run方法的代码
public ConfigurableApplicationContext run(String... args) { ....... try { ...... //我们来看这个context的创建，context=new AnnotationConfigServletWebServerApplicationContext()下面来具体看这块的执行 context = createApplicationContext(); ...... //后续几个部分会来说明这个方法 refreshContext(context); ...... } catch (Throwable ex) { ...... } try { ....... } catch (Throwable ex) { ....... } return context; }createApplicationContext()依次会调用如下方法
protected ConfigurableApplicationContext createApplicationContext() { //这里的this.webApplicationType就是上面的WebApplicationType.SERVLET return this.applicationContextFactory.create(this.webApplicationType); }//最终会调用到这个lambda表达式，入参就是上面的WebApplicationType.SERVLET ApplicationContextFactory DEFAULT = (webApplicationType) -> { try { switch (webApplicationType) { case SERVLET: //会从这里返回 return new AnnotationConfigServletWebServerApplicationContext(); case REACTIVE: return new AnnotationConfigReactiveWebServerApplicationContext(); default: return new AnnotationConfigApplicationContext(); } } catch (Exception ex) { throw new IllegalStateException("Unable create a default ApplicationContext instance, " + "you may need a custom ApplicationContextFactory", ex); } };到这里，我们的上下文context就已经创建出来了，这块代码也比较简单。就不多说什么了
2、查找ServletWebServerFactory
再次回到new SpringApplication(primarySources).run(args)的调用来看run方法的代码
public ConfigurableApplicationContext run(String... args) { ....... try { ...... //上面已经对context做过了讲解，context=new AnnotationConfigServletWebServerApplicationContext() context = createApplicationContext(); ...... //下面来看这个方法 refreshContext(context); ...... } catch (Throwable ex) { ...... } try { ....... } catch (Throwable ex) { ....... } return context; }点到refreshContext(context)
private void refreshContext(ConfigurableApplicationContext context) { if (this.registerShutdownHook) { shutdownHook.registerApplicationContext(context); } refresh(context); }继续点到refresh(context)
protected void refresh(ConfigurableApplicationContext applicationContext) { //这里的applicationContext就是AnnotationConfigServletWebServerApplicationContext的对象，由于这个类没有refresh方法，会跳转到它的父类ServletWebServerApplicationContext的方法中去,我们继续点进去 applicationContext.refresh(); }点到ServletWebServerApplicationContext的refresh方法
public final void refresh() throws BeansException, IllegalStateException { try { //继续跳转到父类AbstractApplicationContext方法 super.refresh(); } catch (RuntimeException ex) { WebServer webServer = this.webServer; if (webServer != null) { webServer.stop(); } throw ex; } }打开AbstractApplicationContext的refresh方法
//springboot 大部分的初始化工作是在这里完成的，不过这不是我们本地的重点，不相关的我们统统略过public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { ...... try { ...... //继续点到这个方法，这里又会跳转到ServletWebServerApplicationContext这个类的方法 onRefresh(); ..... } catch (BeansException ex) { ..... } finally { ..... } } }打开ServletWebServerApplicationContext的onRefresh方法
protected void onRefresh() { super.onRefresh(); try { //这里就是我们本次的重点，会在这里创建具体的web容器，我们点进去看看，还是ServletWebServerApplicationContext这个类的方法 createWebServer(); } catch (Throwable ex) { throw new ApplicationContextException("Unable to start web server", ex); } }打开ServletWebServerApplicationContext的createWebServer方法
private void createWebServer() { WebServer webServer = this.webServer; ServletContext servletContext = getServletContext(); //第一次进来webServer servletContext都是null,会进到if分支里面 if (webServer == null && servletContext == null) { //这里只是做个标记，不用关注，跳过 StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create"); //这里就会来查找ServletWebServerFactory，也就是web容器的工厂,具体看下getWebServerFactory()方法，还是ServletWebServerApplicationContext这个类的方法 ServletWebServerFactory factory = getWebServerFactory(); createWebServer.tag("factory", factory.getClass().toString()); this.webServer = factory.getWebServer(getSelfInitializer()); createWebServer.end(); getBeanFactory().registerSingleton("webServerGracefulShutdown", new WebServerGracefulShutdownLifecycle(this.webServer)); getBeanFactory().registerSingleton("webServerStartStop", new WebServerStartStopLifecycle(this, this.webServer)); } else if (servletContext != null) { try { getSelfInitializer().onStartup(servletContext); } catch (ServletException ex) { throw new ApplicationContextException("Cannot initialize servlet context", ex); } } initPropertySources(); }打开ServletWebServerApplicationContext的getWebServerFactory方法
protected ServletWebServerFactory getWebServerFactory() { // Use bean names so that we don't consider the hierarchy //从beanFactory中查找ServletWebServerFactory类型的bean的定义，返回对应bean的名字 String[] beanNames = getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class); if (beanNames.length == 0) { throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to missing " + "ServletWebServerFactory bean."); } if (beanNames.length > 1) { throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple " + "ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames)); } //这里会从beanFactory中返回bean的名字为beanNames[0],类型为ServletWebServerFactory.class的bean对象，如果当前bean还未创建，则此时就会创建bean对象并返回 return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class); }从上面的代码并看不出来实际的ServletWebServerFactory对象具体是什么？下面带着大家一起简单过下这部分的加载，这里具体就是springboot 加载bean的流程了，这部分的逻辑比较多，本次就不具体展开。关于springboot 加载bean的流程计划后续专门再写一篇。
springboot在启动过程中会在当前类路径下META-INF/spring.factories这个文件中，key=org.springframework.boot.autoconfigure.EnableAutoConfiguration的属性的作为bean的定义进行加载，在这过程中还会使用key=org.springframework.boot.autoconfigure.AutoConfigurationImportFilterfilter的属性作为过滤，配合META-INF/spring-autoconfigure-metadata.properties对这些类做一个过滤，剔除掉不符合的类(后续还会根据类上的注解判断是否要继续剔除)。
当前这些主要在spring-boot-autoconfigure-2.5.1.jar这个文件中
下面截取上面说的两部分,可以看到这里的过滤器就3个，具体不展开讨论了，自动导入的类就是下面的再加过滤去掉的
# Auto Configuration Import Filtersorg.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\org.springframework.boot.autoconfigure.condition.OnBeanCondition,\org.springframework.boot.autoconfigure.condition.OnClassCondition,\org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition# Auto Configureorg.springframework.boot.autoconfigure.EnableAutoConfiguration=\......#下面这个会在创建servelt中使用，下部分我们再关注它org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\#下面这个就是我们需要用到的org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\......org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\......我们看下上面的org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration这个类，这个类在web 场景下，不会被剔除。会被加载。我们看看这个类，我们只看头部就可以了
这里我们看到类上有Import注解，会继续导入这几个类，
ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,ServletWebServerFactoryConfiguration.EmbeddedJetty.class,ServletWebServerFactoryConfiguration.EmbeddedUndertow.class这三个都是本次相关的，它们都是ServletWebServerFactoryConfiguration的内部类，我们进去看看，类的结构都是一样的，我们就看下ServletWebServerFactoryConfiguration.EmbeddedTomcat类吧
可以看到EmbeddedTomcat上面有ConditionalOnClass，ConditionalOnMissingBean这两个注解，
简单说下，ConditionalOnClass是表示当前类路径下存在对应类是加载
ConditionalOnMissingBean是表示当前beanFactory中没有对应类型bean定义的话加载
多个条件都是and的关系，有一个条件不成立，就不会去进行后续处理。
在这里EmbeddedTomcat类这两个条件是成立的，这时就会继续遍历当前类的所有方法，找到@Bean注解的方法，加载到beanFactory中去
而EmbeddedJetty，EmbeddedUndertow两个类条件是不成立的，就不会进行后续执行，剔除掉了
这里就会把EmbeddedTomcat.tomcatServletWebServerFactory这个方法进行加载，返回值是TomcatServletWebServerFactory类型，我们看下TomcatServletWebServerFactory类的继承图,可以看到它正好是继承了ServletWebServerFactory接口。
再次打开ServletWebServerApplicationContext的getWebServerFactory方法
protected ServletWebServerFactory getWebServerFactory() { ....... //所以这里的逻辑实际上会执行ServletWebServerFactoryConfiguration.EmbeddedTomcat类的tomcatServletWebServerFactory方法，返回TomcatServletWebServerFactory对象,相关的属性注入等等这里就不讲述了 return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class); }到这里，整个ServletWebServerFactory的查找就完成了
3、创建DispatcherServletRegistrationBean，DispatcherServlet
再看看上面的META-INF/spring.factories文件
# Auto Configuration Import Filtersorg.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\org.springframework.boot.autoconfigure.condition.OnBeanCondition,\org.springframework.boot.autoconfigure.condition.OnClassCondition,\org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition# Auto Configureorg.springframework.boot.autoconfigure.EnableAutoConfiguration=\......#现在我们重点来看这个类org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\......org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\......我们打开org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration这个类看看
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)@Configuration(proxyBeanMethods = false)//我们当前只关注这ConditionalOnWebApplication、ConditionalOnClass注解//ConditionalOnWebApplication是根据type来判断指定类是否存在//当前的type是 Type.SERVLET，是来查找org.springframework.web.context.support.GenericWebApplicationContext类是否存在，这个类存在于spring-web中，所以这个条件是true@ConditionalOnWebApplication(type = Type.SERVLET)//这个注解上面说过了 ，就是查找指定的类是否存在，这个是查找DispatcherServlet.class是否存在，这里也会返回true@ConditionalOnClass(DispatcherServlet.class)//上面两个条件都成立，就会执行后续的操作，去遍历内部类和方法@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)public class DispatcherServletAutoConfiguration { /** * The bean name for a DispatcherServlet that will be mapped to the root URL "/". */ public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet"; /** * The bean name for a ServletRegistrationBean for the DispatcherServlet "/". */ public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration"; @Configuration(proxyBeanMethods = false) //这里还是个条件，通过实现Condition接口，通过matches方法来判断 //DefaultDispatcherServletCondition这个类就在当前这个文件里，matches判断的结果也是true @Conditional(DefaultDispatcherServletCondition.class) //ServletRegistration.class这个类存在于tomcat-embed-core里面，这个结果也是true @ConditionalOnClass(ServletRegistration.class) //上面两个条件成立，就会执行后续的操作，去遍历内部类和方法 @EnableConfigurationProperties(WebMvcProperties.class) protected static class DispatcherServletConfiguration { //beanFactory会创建这个DispatcherServletbean的定义，bean的名字就是dispatcherServlet @Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME) public DispatcherServlet dispatcherServlet(WebMvcProperties webMvcProperties) { DispatcherServlet dispatcherServlet = new DispatcherServlet(); dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest()); dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest()); dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound()); dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents()); dispatcherServlet.setEnableLoggingRequestDetails(webMvcProperties.isLogRequestDetails()); return dispatcherServlet; } @Bean @ConditionalOnBean(MultipartResolver.class) @ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME) public MultipartResolver multipartResolver(MultipartResolver resolver) { // Detect if the user has created a MultipartResolver but named it incorrectly return resolver; } } @Configuration(proxyBeanMethods = false) //和上面的一样，不说了 @Conditional(DispatcherServletRegistrationCondition.class) //和上面的一样，不说了 @ConditionalOnClass(ServletRegistration.class) @EnableConfigurationProperties(WebMvcProperties.class) //这里会要在查找DispatcherServletConfiguration.class，并执行加载bean定义的流程，这就是上面的类了 @Import(DispatcherServletConfiguration.class) protected static class DispatcherServletRegistrationConfiguration { @Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME) //ConditionalOnBean查找是否存在指定bean的定义，这个方法要注入参数，需要这个类，当前这里就是上面的dispatcherServlet方法定义的，这里也是存在的 @ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME) //DispatcherServlet dispatcherServlet这个就是dispatcherServlet这个方法定义的bean，在创建DispatcherServletRegistrationBean这个bean的时候，就会去查找dispatcherServlet是否存在，如果不存在，先创建dispatcherServlet这个bean,再创建DispatcherServletRegistrationBean public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet, WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) { DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet, webMvcProperties.getServlet().getPath()); registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME); registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup()); multipartConfig.ifAvailable(registration::setMultipartConfig); return registration; } } ......}上面就是创建DispatcherServlet，DispatcherServletRegistrationBean的过程了
4、创建tomcat，加载Servlet.class,filter.class，监听器
再次回到ServletWebServerApplicationContext的createWebServer方法
private void createWebServer() { WebServer webServer = this.webServer; ServletContext servletContext = getServletContext(); if (webServer == null && servletContext == null) { StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create"); //上面我们已经看到了这里，factory是TomcatServletWebServerFactory类的一个实例对象 ServletWebServerFactory factory = getWebServerFactory(); //这里还是做个标记，不用关注 createWebServer.tag("factory", factory.getClass().toString()); //这里就是具体创建tomcat了，这里的入参getSelfInitializer()是个lambda表达式，这个后续很重要 this.webServer = factory.getWebServer(getSelfInitializer()); createWebServer.end(); getBeanFactory().registerSingleton("webServerGracefulShutdown", new WebServerGracefulShutdownLifecycle(this.webServer)); getBeanFactory().registerSingleton("webServerStartStop", new WebServerStartStopLifecycle(this, this.webServer)); } else if (servletContext != null) { try { getSelfInitializer().onStartup(servletContext); } catch (ServletException ex) { throw new ApplicationContextException("Cannot initialize servlet context", ex); } } initPropertySources(); }private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() { return this::selfInitialize; } //是创建webServer的参数 private void selfInitialize(ServletContext servletContext) throws ServletException { prepareWebApplicationContext(servletContext); registerApplicationScope(servletContext); WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext); for (ServletContextInitializer beans : getServletContextInitializerBeans()) { beans.onStartup(servletContext); } }factory.getWebServer(getSelfInitializer())会调用到TomcatServletWebServerFactory的getWebServer的方法
public WebServer getWebServer(ServletContextInitializer... initializers) { ....... //上面的入参会在这里传下去 prepareContext(tomcat.getHost(), initializers); return getTomcatWebServer(tomcat); }点进prepareContext(tomcat.getHost(), initializers)去看看
protected void prepareContext(Host host, ServletContextInitializer[] initializers) { ...... ServletContextInitializer[] initializersToUse = mergeInitializers(initializers); host.addChild(context); //继续传下去 configureContext(context, initializersToUse); postProcessContext(context); }再点到configureContext(context, initializersToUse)这个调用去看看
protected void configureContext(Context context, ServletContextInitializer[] initializers) { //会传递给TomcatStarter，作为构造参数，下面我们去这里看看 TomcatStarter starter = new TomcatStarter(initializers); ...... }下面我们去看看TomcatStarter这个类是怎么使用这个initializers这个构造参数的。
这个类不长class TomcatStarter implements ServletContainerInitializer { ...... TomcatStarter(ServletContextInitializer[] initializers) { //入参会作为它的成员属性 this.initializers = initializers; } @Override public void onStartup(Set<Class<?>> classes, ServletContext servletContext) throws ServletException { try { for (ServletContextInitializer initializer : this.initializers) { //会在这里调用onStartup方法，这里的入参就是ApplicationContextFacade的对象，里面包装了ApplicationContext，里面再包装了TomcatEmbeddedContext，这要就和tomcat联系起来了，下面的截图就是servletContext的对象结构 initializer.onStartup(servletContext); } } catch (Exception ex) { ...... }
上面的initializer.onStartup(servletContext)会调用到ServletWebServerApplicationContext的selfInitialize方法
private void selfInitialize(ServletContext servletContext) throws ServletException { //这里是将ApplicationContextFacade设置到当前的servletContext上 prepareWebApplicationContext(servletContext); //这里是在beanFactory中注册application的scope registerApplicationScope(servletContext); //这里还是注册上下文相关的bean WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext); //我们重点来看这里getServletContextInitializerBeans()是定义个一个ServletContextInitializerBeans对象，我们点进去看看 for (ServletContextInitializer beans : getServletContextInitializerBeans()) { beans.onStartup(servletContext); } }protected Collection<ServletContextInitializer> getServletContextInitializerBeans() { //这里的getBeanFactory()就是全局的beanFactory return new ServletContextInitializerBeans(getBeanFactory()); }public ServletContextInitializerBeans(ListableBeanFactory beanFactory, Class<? extends ServletContextInitializer>... initializerTypes) { this.initializers = new LinkedMultiValueMap<>(); //由于我们没有传initializerTypes这个参数，所以this.initializerTypes里面就只有ServletContextInitializer.class这个类 this.initializerTypes = (initializerTypes.length != 0) ? Arrays.asList(initializerTypes) : Collections.singletonList(ServletContextInitializer.class); //这里主要是从beanFactory中查找this.initializerTypes类型，我们进去看看，就是下面这个方法了 addServletContextInitializerBeans(beanFactory); addAdaptableBeans(beanFactory); List<ServletContextInitializer> sortedInitializers = this.initializers.values().stream() .flatMap((value) -> value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE)) .collect(Collectors.toList()); this.sortedList = Collections.unmodifiableList(sortedInitializers); logMappings(this.initializers); } private void addServletContextInitializerBeans(ListableBeanFactory beanFactory) { for (Class<? extends ServletContextInitializer> initializerType : this.initializerTypes) { //默认情况下这里找到就只有上面第3部分的DispatcherServletRegistrationBean对应的bean for (Entry<String, ? extends ServletContextInitializer> initializerBean : getOrderedBeansOfType(beanFactory, initializerType)) { //这里的key是bean的名字,value就是bean对象，在进去看看，就是下面这个方法 addServletContextInitializerBean(initializerBean.getKey(), initializerBean.getValue(), beanFactory); } } } private void addServletContextInitializerBean(String beanName, ServletContextInitializer initializer, ListableBeanFactory beanFactory) { //会走到这个分支 if (initializer instanceof ServletRegistrationBean) { //这里返回的servlet也还是第3部分DispatcherServlet对应的bean Servlet source = ((ServletRegistrationBean<?>) initializer).getServlet(); //再点进去 addServletContextInitializerBean(Servlet.class, beanName, initializer, beanFactory, source); } else if (initializer instanceof FilterRegistrationBean) { Filter source = ((FilterRegistrationBean<?>) initializer).getFilter(); addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source); } else if (initializer instanceof DelegatingFilterProxyRegistrationBean) { String source = ((DelegatingFilterProxyRegistrationBean) initializer).getTargetBeanName(); addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source); } else if (initializer instanceof ServletListenerRegistrationBean) { EventListener source = ((ServletListenerRegistrationBean<?>) initializer).getListener(); addServletContextInitializerBean(EventListener.class, beanName, initializer, beanFactory, source); } else { addServletContextInitializerBean(ServletContextInitializer.class, beanName, initializer, beanFactory, initializer); } } private void addServletContextInitializerBean(Class<?> type, String beanName, ServletContextInitializer initializer, ListableBeanFactory beanFactory, Object source) { //这里的initializers是个map,按照类型，bean对象进行加载，这里的type是javax.servlet.Servlet.class,value是上面的DispatcherServletRegistrationBean this.initializers.add(type, initializer); if (source != null) { // Mark the underlying source as seen in case it wraps an existing bean //将DispatcherServlet对应的bean加到这里 this.seen.add(source); } if (logger.isTraceEnabled()) { String resourceDescription = getResourceDescription(beanName, beanFactory); int order = getOrder(initializer); logger.trace("Added existing " + type.getSimpleName() + " initializer bean '" + beanName + "'; order=" + order + ", resource=" + resourceDescription); } }再回到ServletContextInitializerBeans的构造方法,接着看后面的
public ServletContextInitializerBeans(ListableBeanFactory beanFactory, Class<? extends ServletContextInitializer>... initializerTypes) { ...... //这里的内容上面已经看过了，我们现在看下面这句，点进去 addAdaptableBeans(beanFactory); List<ServletContextInitializer> sortedInitializers = this.initializers.values().stream() .flatMap((value) -> value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE)) .collect(Collectors.toList()); this.sortedList = Collections.unmodifiableList(sortedInitializers); logMappings(this.initializers); }protected void addAdaptableBeans(ListableBeanFactory beanFactory) { //这句不用关注 MultipartConfigElement multipartConfig = getMultipartConfig(beanFactory); //这句不用关注 addAsRegistrationBean(beanFactory, Servlet.class, new ServletRegistrationBeanAdapter(multipartConfig)); //点到这里去看看 addAsRegistrationBean(beanFactory, Filter.class, new FilterRegistrationBeanAdapter()); for (Class<?> listenerType : ServletListenerRegistrationBean.getSupportedTypes()) { addAsRegistrationBean(beanFactory, EventListener.class, (Class<EventListener>) listenerType, new ServletListenerRegistrationBeanAdapter()); } }private <T, B extends T> void addAsRegistrationBean(ListableBeanFactory beanFactory, Class<T> type, Class<B> beanType, RegistrationBeanAdapter<T> adapter) { //这里的beanType是 Filter.class,下面这句就是从beanFactory中获取所有类型为Filter.class的bean List<Map.Entry<String, B>> entries = getOrderedBeansOfType(beanFactory, beanType, this.seen); for (Entry<String, B> entry : entries) { String beanName = entry.getKey(); B bean = entry.getValue(); //将bean放置到this.seen里面 if (this.seen.add(bean)) { // One that we haven't already seen //包装成RegistrationBean对象 RegistrationBean registration = adapter.createRegistrationBean(beanName, bean, entries.size()); int order = getOrder(bean); registration.setOrder(order); //同样放置到this.initializers里面 this.initializers.add(type, registration); if (logger.isTraceEnabled()) { logger.trace("Created " + type.getSimpleName() + " initializer for bean '" + beanName + "'; order=" + order + ", resource=" + getResourceDescription(beanName, beanFactory)); } } } }再回到上面的addAdaptableBeans方法，看后面的
protected void addAdaptableBeans(ListableBeanFactory beanFactory) { ......//这里刚才说过了 //下面这部分不说了，这里基本和上面一样，不过处理的类型变成了ServletContextAttributeListener.class、ServletRequestListener.class、ServletRequestAttributeListener.class、HttpSessionAttributeListener.class、HttpSessionIdListener.class、HttpSessionListener.class、ServletContextListener.class这些类型 for (Class<?> listenerType : ServletListenerRegistrationBean.getSupportedTypes()) { addAsRegistrationBean(beanFactory, EventListener.class, (Class<EventListener>) listenerType, new ServletListenerRegistrationBeanAdapter()); } }再回到ServletContextInitializerBeans的构造方法,接着看后面的
public ServletContextInitializerBeans(ListableBeanFactory beanFactory, Class<? extends ServletContextInitializer>... initializerTypes) { ......//这里刚才都说过了，看下面 //这里就是把上面所有获取到的相关的bean放置到this.sortedList中，下面我是我本地this.sortedList的截图 List<ServletContextInitializer> sortedInitializers = this.initializers.values().stream() .flatMap((value) -> value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE)) .collect(Collectors.toList()); this.sortedList = Collections.unmodifiableList(sortedInitializers); logMappings(this.initializers); }
这里ServletContextInitializerBeans的构造方法就完成了，再回过头去看看这个类的定义
public class ServletContextInitializerBeans extends AbstractCollection<ServletContextInitializer>这个类继承了AbstractCollection类，那它就需要实现下面这个抽象方法
public abstract Iterator<E> iterator();我们看看ServletContextInitializerBeans的iterator的方法
@Overridepublic Iterator<ServletContextInitializer> iterator() { return this.sortedList.iterator();}看到了吧，这就是返回上面的this.sortedList.iterator()
我们再次回到ServletWebServerApplicationContext的selfInitialize方法
private void selfInitialize(ServletContext servletContext) throws ServletException { ......//这里上面都说过了 //getServletContextInitializerBeans()这个方法就是构造了ServletContextInitializerBeans //这里的for循环也是调用了ServletContextInitializerBeans的iterator的方法，实际上遍历的也就是上面的this.sortedList for (ServletContextInitializer beans : getServletContextInitializerBeans()) { //这里就是把在beanFactory中查找到的Servlet.class,filter.class，监听器等等添加到tomcat容器中,我们就只进到servlet里面去看看 //进到DispatcherServletRegistrationBean里面去看看 beans.onStartup(servletContext); }}//这个方法在DispatcherServletRegistrationBean的父类RegistrationBean中 //所有的Servlet.class,filter.class，监听器都会走到这里 public final void onStartup(ServletContext servletContext) throws ServletException { //这里是返回的表述，不关注 String description = getDescription(); if (!isEnabled()) { logger.info(StringUtils.capitalize(description) + " was not registered (disabled)"); return; } //这里由不同的子类去实现，DispatcherServletRegistrationBean会调用到ServletRegistrationBean中 register(description, servletContext); }//这个方法是在ServletRegistrationBean这个类中 @Override protected ServletRegistration.Dynamic addRegistration(String description, ServletContext servletContext) { String name = getServletName(); //这里的servletContext上面的ApplicationContextFacade的对象，这里就会将DispatcherServlet的bean对象加载到TomcatEmbeddedContext中，后续所有的http请求最后都会流转到DispatcherServlet去进行具体的分发 return servletContext.addServlet(name, this.servlet); }到这里Servlet.class,filter.class，监听器就全部加载到tomcat中去
5、创建RequestMappingHandlerMapping
再看看上面的META-INF/spring.factories文件
# Auto Configuration Import Filtersorg.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\org.springframework.boot.autoconfigure.condition.OnBeanCondition,\org.springframework.boot.autoconfigure.condition.OnClassCondition,\org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition# Auto Configureorg.springframework.boot.autoconfigure.EnableAutoConfiguration=\......org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\......#现在我们重点来看这个类org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\......具体的加载和上面部分都类似，就不展开了，直接看我们需要的
//这里会创建RequestMappingHandlerMapping的bean @Bean @Primary @Override public RequestMappingHandlerMapping requestMappingHandlerMapping( @Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager, @Qualifier("mvcConversionService") FormattingConversionService conversionService, @Qualifier("mvcResourceUrlProvider") ResourceUrlProvider resourceUrlProvider) { // Must be @Primary for MvcUriComponentsBuilder to work return super.requestMappingHandlerMapping(contentNegotiationManager, conversionService, resourceUrlProvider);看下这个类的继承图
RequestMappingHandlerMapping实现了InitializingBean接口，会在bean对象创建后的invokeInitMethods方法中调用afterPropertiesSet方法,最终会调用的AbstractHandlerMethodMapping的afterPropertiesSet方法中
@Override public void afterPropertiesSet() { initHandlerMethods(); } /** * Scan beans in the ApplicationContext, detect and register handler methods. * @see #getCandidateBeanNames() * @see #processCandidateBean * @see #handlerMethodsInitialized */ protected void initHandlerMethods() { //这里查找beanFactory中的所有bean进行遍历 for (String beanName : getCandidateBeanNames()) { if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) { //点到这里去看看 processCandidateBean(beanName); } } handlerMethodsInitialized(getHandlerMethods()); }protected void processCandidateBean(String beanName) { Class<?> beanType = null; try { //根据beanName获取对应bean的Class对象 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); } } //判断类上是否有Controller.class，RequestMapping.class注解 if (beanType != null && isHandler(beanType)) { //这里就会解析beanName上的所有方法进行遍历，查找有 RequestMapping.class注解的方法，创建RequestMappingInfo对象，放置到registry属性中(在AbstractHandlerMethodMapping)中，这样我们所有定义的controller中的http请求就会全部被扫描到 detectHandlerMethods(beanName); } }6、加载RequestMappingHandlerMapping到DispatcherServlet中
在我们第一次请求的时候，会执行到DispatcherServlet的initStrategies方法，这个方法只会执行一次
protected void initStrategies(ApplicationContext context) { ...... 这就会加载之前查找到的RequestMappingHandlerMapping中的我们定义的controller initHandlerMappings(context); ...... }会调用到这里
private void initHandlerMappings(ApplicationContext context) { this.handlerMappings = null; if (this.detectAllHandlerMappings) { // Find all HandlerMappings in the ApplicationContext, including ancestor contexts. //这里会在beanFactory中查找所有HandlerMapping.class的bean,其中就包含我们第5部分的RequestMappingHandlerMapping Map<String, HandlerMapping> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false); if (!matchingBeans.isEmpty()) { //将所有查找到的放置到handlerMappings中 this.handlerMappings = new ArrayList<>(matchingBeans.values()); // We keep HandlerMappings in sorted order. AnnotationAwareOrderComparator.sort(this.handlerMappings); } } ...... }当我们浏览器请求的时候，最终会走到DispatcherServlet的doDispatch的方法，处理我们的请求并返回,简单看看
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception { ...... try { ModelAndView mv = null; Exception dispatchException = null; try { processedRequest = checkMultipart(request); multipartRequestParsed = (processedRequest != request); // Determine handler for the current request. //在这里，就会请求request的请求路径去查找实际要执行的controller的方法，点进去看看 mappedHandler = getHandler(processedRequest); ...... }@Nullable protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { if (this.handlerMappings != null) { //这其实就是根据遍历，查找对应的路径，这个this.handlerMappings就是就是在initHandlerMappings方法中赋值的 for (HandlerMapping mapping : this.handlerMappings) { HandlerExecutionChain handler = mapping.getHandler(request); if (handler != null) { return handler; } } } return null; }到这里，springboot 加载web容器的整个流程基本就算完成了，这块涉及的东西比较多，所以说的可能比较粗，大家见谅。