Spring Boot启动过程完全解析（二）

上篇给大家介绍了Spring Boot启动过程完全解析(一)，大家可以点击参考下

　　该说refreshContext(context)了，首先是判断context是否是AbstractApplicationContext派生类的实例，之后调用了强转为AbstractApplicationContext类型并调用它的refresh方法。由于AnnotationConfigEmbeddedWebApplicationContext继承自EmbeddedWebApplicationContext，所以会执行EmbeddedWebApplicationContext的refresh方法，继而执行其中的super.refresh。这个refresh也就是AbstractApplicationContext的refresh方法了，它内部是一个synchronized锁全局的代码块，同样的加锁方法还有这个类里的close和registerShutdownHook方法。

　　同步代码块中第一个方法prepareRefresh，首先会执行AnnotationConfigEmbeddedWebApplicationContext的prepareRefresh方法：

 protected void prepareRefresh() {
  this.scanner.clearCache();
  super.prepareRefresh();
 }

　　这个super也就是AbstractApplicationContext，它的prepareRefresh方法逻辑是：生成启动时间；设置closed状态为false；active状态为true；initPropertySources方法主要是调用了AbstractEnvironment的getPropertySources方法获取了之前SpringApplication的prepareEnvironment方法中getOrCreateEnvironment方法准备的各种环境变量及配置并用于初始化ServletPropertySources。具体的servletContextInitParams这些是在环境对象初始化时由各集成级别Environment的customizePropertySources方法中初始化的。

　　接着的getEnvironment().validateRequiredProperties()方法实际执行了AbstractEnvironment中的this.propertyResolver.validateRequiredProperties()，主要是验证了被占位的key如果是required的值不能为null。prepareRefresh的最后是初始化this.earlyApplicationEvents = new LinkedHashSet<ApplicationEvent>()。*****

　　只够是获取BeanFactory实例的方法obtainFreshBeanFactory()，首先在refreshBeanFactory方法中用原子布尔类型判断是否刷新过，BeanFactory实例是在createApplicationContext创建Context实例时被创建的，如果没有刷新则设置一个用于序列化的id，id是ContextIdApplicationContextInitializer初始化设置的（如未配置该初始化器，是有一个默认ObjectUtils.identityToString(this)生成的），这个id的生成规则是spring.config.name截取的+":"+server.port的占位截取。设置序列化id时，同时保存了一个id和弱引用DefaultListableBeanFactory实例映射。

　　得到了beanFactory后就是prepareBeanFactory(beanFactory)了，逻辑是注册了BeanClassLoader用于注入的bean实例的创建；StandardBeanExpressionResolver用于EL表达式，比如配置文件或者@Value("#{...}")等使用；用ResourceEditorRegistrar注册属性转换器，比如xml配置的bean属性都是用的字符串配置的要转成真正的属性类型；addBeanPostProcessor(new ApplicationContextAwareProcessor(this))注册ApplicationContextAwareProcessor，它的invokeAwareInterfaces方法会对实现指定接口的bean调用指定的set方法；ignoreDependencyInterface忽略对这些接口的自动装配，比如Aware这些是要做独立处理的，不适合通用的方法；然后是有几个类型直接手动注册，比如BeanFactory，这个很好理解；接着注册一个后置处理器ApplicationListenerDetector的实例，addBeanPostProcessor注册的会按照注册先后顺序执行；这个方法的最后判断了特定的4个bean名字，如果存在会做相应注册，包括loadTimeWeaver、environment、systemProperties和systemEnvironment。补充一点，在最开始创建实例的时候还执行过ignoreDependencyInterface(BeanNameAware.class);ignoreDependencyInterface(BeanFactoryAware.class);ignoreDependencyInterface(BeanClassLoaderAware.class)。

 protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
  // Tell the internal bean factory to use the context's class loader etc.
  beanFactory.setBeanClassLoader(getClassLoader());
  beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
  beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
  // Configure the bean factory with context callbacks.
  beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
  beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
  beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
  beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
  beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
  beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
  beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
  // BeanFactory interface not registered as resolvable type in a plain factory.
  // MessageSource registered (and found for autowiring) as a bean.
  beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
  beanFactory.registerResolvableDependency(ResourceLoader.class, this);
  beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
  beanFactory.registerResolvableDependency(ApplicationContext.class, this);
  // Register early post-processor for detecting inner beans as ApplicationListeners.
  beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
  // Detect a LoadTimeWeaver and prepare for weaving, if found.
  if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
   beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
   // Set a temporary ClassLoader for type matching.
   beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
  }
  // Register default environment beans.
  if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
   beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
  }
  if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
   beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
  }
  if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
   beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
  }
 }

　　之后到了refresh的postProcessBeanFactory方法，首先是会走到AnnotationConfigEmbeddedWebApplicationContext的Override，需要注意的一点是，这是web环境，如果不是是不会加载这个上下文的，也就不会这么走。它重写的第一步是先走super也就是EmbeddedWebApplicationContext的postProcessBeanFactory，这里又注册了个后置处理器WebApplicationContextServletContextAwareProcessor的实例，构造参数是this，也就是当前上下文，同时忽略ServletContextAware接口，这个接口是用于获取ServletContext的，为什么要忽略呢，我猜应该是因为我们既然有了web应用并且内嵌servlet的上下文实例，还要ServletContext的实现就没什么用了，还有可能出现冲突的问题，有空我再确认下。然后是配置的basePackages和annotatedClasses：

@Override
 protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
  super.postProcessBeanFactory(beanFactory);
  if (this.basePackages != null && this.basePackages.length > 0) {
   this.scanner.scan(this.basePackages);
  }
  if (this.annotatedClasses != null && this.annotatedClasses.length > 0) {
   this.reader.register(this.annotatedClasses);
  }
 }

　　到了invokeBeanFactoryPostProcessors方法，这个方法就是执行之前注册的BeanFactory后置处理器的地方。代码一目了然，PostProcessorRegistrationDelegate的invokeBeanFactoryPostProcessors中只是有些排序的逻辑，我就不说了：

 /**
  * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
  * respecting explicit order if given.
  * <p>Must be called before singleton instantiation.
  */
 protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
  PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
  // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
  // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
  if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
   beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
   beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
  }
 }

　　BeanFactory后置处理器执行之后是注册Bean的后置处理器方法registerBeanPostProcessors。例如new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount)会在Bean没有合适的后置处理器时记条info级日志。ApplicationListenerDetector也注册了一个。

　　initMessageSource这个方法在我这没什么用，都说是国际化的，随便百度一下一堆一堆的，而且其实严格来说这篇多数不属于spring boot的部分，这方法我就不细写了。

　　initApplicationEventMulticaster方法主要也就是初始化并注册applicationEventMulticaster的这两句代码：

this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
   beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);

　　onRefresh也是根据环境不同加载的上下文不同而不同的，用于支持子类扩展出来的上下文特定的逻辑的。EmbeddedWebApplicationContext的onRefresh首先依然是super.onRefresh，逻辑就是初始化了主题；

createEmbeddedServletContainer方法名我就不翻译了，一般情况下是使用getBeanFactory .getBeanNamesForType方法找到EmbeddedServletContainerFactory类型的实例，这也就是我之前那个问题解决过程中，为什么只要排除掉tomcat引用，引入jetty引用就可以自动换成jetty的原因。创建容器的过程中初始化方法selfInitialize注册了filter和MappingForUrlPatterns等，代码在AbstractFilterRegistrationBean等onStartup，这里就不细说了，如果能抽出时间说说之前查问题的时候查的容器代码再说。然后初始化PropertySources，servletContextInitParams和servletConfigInitParams：

 public static void initServletPropertySources(
   MutablePropertySources propertySources, ServletContext servletContext, ServletConfig servletConfig) {
  Assert.notNull(propertySources, "'propertySources' must not be null");
  if (servletContext != null && propertySources.contains(StandardServletEnvironment.SERVLET_CONTEXT_PROPERTY_SOURCE_NAME) &&
    propertySources.get(StandardServletEnvironment.SERVLET_CONTEXT_PROPERTY_SOURCE_NAME) instanceof StubPropertySource) {
   propertySources.replace(StandardServletEnvironment.SERVLET_CONTEXT_PROPERTY_SOURCE_NAME,
     new ServletContextPropertySource(StandardServletEnvironment.SERVLET_CONTEXT_PROPERTY_SOURCE_NAME, servletContext));
  }
  if (servletConfig != null && propertySources.contains(StandardServletEnvironment.SERVLET_CONFIG_PROPERTY_SOURCE_NAME) &&
    propertySources.get(StandardServletEnvironment.SERVLET_CONFIG_PROPERTY_SOURCE_NAME) instanceof StubPropertySource) {
   propertySources.replace(StandardServletEnvironment.SERVLET_CONFIG_PROPERTY_SOURCE_NAME,
     new ServletConfigPropertySource(StandardServletEnvironment.SERVLET_CONFIG_PROPERTY_SOURCE_NAME, servletConfig));
  }
 }

　　registerListeners首先注册静态监听：

 @Override
 public void addApplicationListener(ApplicationListener<?> listener) {
  synchronized (this.retrievalMutex) {
   this.defaultRetriever.applicationListeners.add(listener);
   this.retrieverCache.clear();
  }
 }

　　接着是：

　registerListeners的最后，初始化过的earlyApplicationEvents如果有事件，这时候会被发布。

　　finishBeanFactoryInitialization结束BeanFactory的初始化并初始化所有非延迟加载的单例。事实上我们自定义的单例Bean都是在这里getBean方法初始化的，所以如果注册的Bean特别多的话，这个过程就是启动过程中最慢的。初始化开始前先设置configurationFrozen为true，并this.frozenBeanDefinitionNames = StringUtils.toStringArray ( this. beanDefinitionNames )。如果有bean实例实现了SmartInitializingSingleton会有后置处理触发，不包括延迟加载的。例如：org.springframework.context.event. internalEventListenerProcessor会触发EventListenerMethodProcessor的afterSingletonsInstantiated方法对所有对象（Object的子类）处理。

　　finishRefresh:Refresh的最后一步，发布相应事件。同样先执行EmbeddedWebApplicationContext中对应方法的super(EmbeddedWebApplicationContext)的对应方法：

 /**
  * Finish the refresh of this context, invoking the LifecycleProcessor's
  * onRefresh() method and publishing the
  * {@link org.springframework.context.event.ContextRefreshedEvent}.
  */
 protected void finishRefresh() {
  // Initialize lifecycle processor for this context.
  initLifecycleProcessor();
  // Propagate refresh to lifecycle processor first.
  getLifecycleProcessor().onRefresh();
  // Publish the final event.
  publishEvent(new ContextRefreshedEvent(this));
  // Participate in LiveBeansView MBean, if active.
  LiveBeansView.registerApplicationContext(this);
 }

　　初始化生命周期处理器，逻辑是判断beanFactory中是否已经注册了lifecycleProcessor，没有就new一个DefaultLifecycleProcessor并setBeanFactory(beanFactory)，然后将它赋值给私有LifecycleProcessor类型的this变量。然后执行生命周期处理器的onRefresh，其中先startBeans，被start的beans是通过getBeanNamesForType(Lifecycle.class, false, false)从beanFactory中取出来的，例如endpointMBeanExporter和lifecycleProcessor，会去调用bean的start方法，endpointMBeanExporter的start中执行 locateAndRegisterEndpoints方法并设置running属性为true，这个过程加了ReentrantLock锁。bean都启动完会设置处理器的running为true。刷新完会发布ContextRefreshedEvent事件，这个事件除了都有的记录时间还执行了ConfigurationPropertiesBindingPostProcessor的freeLocalValidator方法，我这的逻辑是实际上执行了ValidatorFactoryImpl的close方法。这个逻辑的最后会检查一个配置spring.liveBeansView.mbeanDomain是否存在，有就会创建一个MBeanServer：

static void registerApplicationContext(ConfigurableApplicationContext applicationContext) {
  String mbeanDomain = applicationContext.getEnvironment().getProperty(MBEAN_DOMAIN_PROPERTY_NAME);
  if (mbeanDomain != null) {
   synchronized (applicationContexts) {
    if (applicationContexts.isEmpty()) {
     try {
      MBeanServer server = ManagementFactory.getPlatformMBeanServer();
      applicationName = applicationContext.getApplicationName();
      server.registerMBean(new LiveBeansView(),
        new ObjectName(mbeanDomain, MBEAN_APPLICATION_KEY, applicationName));
     }
     catch (Throwable ex) {
      throw new ApplicationContextException("Failed to register LiveBeansView MBean", ex);
     }
    }
    applicationContexts.add(applicationContext);
   }
  }
 }

　　finishRefresh最后会启动前面创建的内嵌容器，并发布EmbeddedServletContainerInitializedEvent事件，启动这一部分算是容器的逻辑了，有机会整理容器逻辑再细写，我这里是Tomcat的：

@Override
 public void start() throws EmbeddedServletContainerException {
  try {
   addPreviouslyRemovedConnectors();
   Connector connector = this.tomcat.getConnector();
   if (connector != null && this.autoStart) {
    startConnector(connector);
   }
   checkThatConnectorsHaveStarted();
   TomcatEmbeddedServletContainer.logger
     .info("Tomcat started on port(s): " + getPortsDescription(true));
  }
  catch (ConnectorStartFailedException ex) {
   stopSilently();
   throw ex;
  }
  catch (Exception ex) {
   throw new EmbeddedServletContainerException(
     "Unable to start embedded Tomcat servlet container", ex);
  }
  finally {
   Context context = findContext();
   ContextBindings.unbindClassLoader(context, getNamingToken(context),
     getClass().getClassLoader());
  }
 }

　　然后是resetCommonCaches：

 /**
  * Reset Spring's common core caches, in particular the {@link ReflectionUtils},
  * {@link ResolvableType} and {@link CachedIntrospectionResults} caches.
  * @since 4.2
  * @see ReflectionUtils#clearCache()
  * @see ResolvableType#clearCache()
  * @see CachedIntrospectionResults#clearClassLoader(ClassLoader)
  */
 protected void resetCommonCaches() {
  ReflectionUtils.clearCache();
  ResolvableType.clearCache();
  CachedIntrospectionResults.clearClassLoader(getClassLoader());
 }

　　refreshContext的最后是注册shutdown的钩子：

 if (this.registerShutdownHook) {
   try {
    context.registerShutdownHook();
   }
   catch (AccessControlException ex) {
    // Not allowed in some environments.
   }
  }

 /**
  * Register a shutdown hook with the JVM runtime, closing this context
  * on JVM shutdown unless it has already been closed at that time.
  * <p>Delegates to {@code doClose()} for the actual closing procedure.
  * @see Runtime#addShutdownHook
  * @see #close()
  * @see #doClose()
  */
 @Override
 public void registerShutdownHook() {
  if (this.shutdownHook == null) {
   // No shutdown hook registered yet.
   this.shutdownHook = new Thread() {
    @Override
    public void run() {
     synchronized (startupShutdownMonitor) {
      doClose();
     }
    }
   };
   Runtime.getRuntime().addShutdownHook(this.shutdownHook);
  }
 }

咱最近用的github：https://github.com/saaavsaaa

以上所述是小编给大家介绍的Spring Boot启动过程完全解析（二），希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对我们网站的支持！