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尚硅谷springboot学习26-嵌入式servlet容器自动配置、启动原理

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作者:因情语写

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  EmbeddedServletContainerAutoConfiguration:嵌入式的Servlet容器自动配

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
@Import(BeanPostProcessorsRegistrar.class)
//导入BeanPostProcessorsRegistrar:Spring注解版;给容器中导入一些组件
//导入了EmbeddedServletContainerCustomizerBeanPostProcessor:
//后置处理器:bean初始化前后(创建完对象,还没赋值赋值)执行初始化工作
public class EmbeddedServletContainerAutoConfiguration {
    
    @Configuration
    @ConditionalOnClass({ Servlet.class, Tomcat.class })//判断当前是否引入了Tomcat依赖;
    @ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)//判断当前容器没有用户自己定义EmbeddedServletContainerFactory:嵌入式的Servlet容器工厂;作用:创建嵌入式的Servlet容器
    public static class EmbeddedTomcat {

        @Bean
        public TomcatEmbeddedServletContainerFactory tomcatEmbeddedServletContainerFactory() {
            return new TomcatEmbeddedServletContainerFactory();
        }

    }
    
    /**
     * Nested configuration if Jetty is being used.
     */
    @Configuration
    @ConditionalOnClass({ Servlet.class, Server.class, Loader.class,
            WebAppContext.class })
    @ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
    public static class EmbeddedJetty {

        @Bean
        public JettyEmbeddedServletContainerFactory jettyEmbeddedServletContainerFactory() {
            return new JettyEmbeddedServletContainerFactory();
        }

    }

    /**
     * Nested configuration if Undertow is being used.
     */
    @Configuration
    @ConditionalOnClass({ Servlet.class, Undertow.class, SslClientAuthMode.class })
    @ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
    public static class EmbeddedUndertow {

        @Bean
        public UndertowEmbeddedServletContainerFactory undertowEmbeddedServletContainerFactory() {
            return new UndertowEmbeddedServletContainerFactory();
        }

    }

  1)、EmbeddedServletContainerFactory(嵌入式Servlet容器工厂)

public interface EmbeddedServletContainerFactory {

   //获取嵌入式的Servlet容器
   EmbeddedServletContainer getEmbeddedServletContainer(
         ServletContextInitializer... initializers);

}

  2)、EmbeddedServletContainer:(嵌入式的Servlet容器)

  3)、以TomcatEmbeddedServletContainerFactory为例

@Override
public EmbeddedServletContainer getEmbeddedServletContainer(
      ServletContextInitializer... initializers) {
    //创建一个Tomcat
   Tomcat tomcat = new Tomcat();
    
    //配置Tomcat的基本环节
   File baseDir = (this.baseDirectory != null ? this.baseDirectory
         : createTempDir("tomcat"));
   tomcat.setBaseDir(baseDir.getAbsolutePath());
   Connector connector = new Connector(this.protocol);
   tomcat.getService().addConnector(connector);
   customizeConnector(connector);
   tomcat.setConnector(connector);
   tomcat.getHost().setAutoDeploy(false);
   configureEngine(tomcat.getEngine());
   for (Connector additionalConnector : this.additionalTomcatConnectors) {
      tomcat.getService().addConnector(additionalConnector);
   }
   prepareContext(tomcat.getHost(), initializers);
    
    //将配置好的Tomcat传入进去,返回一个EmbeddedServletContainer;并且启动Tomcat服务器
   return getTomcatEmbeddedServletContainer(tomcat);
}

  4)、我们对嵌入式容器的配置修改是怎么生效?

ServerProperties、EmbeddedServletContainerCustomizer

  EmbeddedServletContainerCustomizer:定制器帮我们修改了Servlet容器的配置?

  怎么修改的原理?

  5)、容器中导入了EmbeddedServletContainerCustomizerBeanPostProcessor

//初始化之前
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName)
      throws BeansException {
    //如果当前初始化的是一个ConfigurableEmbeddedServletContainer类型的组件
   if (bean instanceof ConfigurableEmbeddedServletContainer) {
       //
      postProcessBeforeInitialization((ConfigurableEmbeddedServletContainer) bean);
   }
   return bean;
}

private void postProcessBeforeInitialization(
            ConfigurableEmbeddedServletContainer bean) {
    //获取所有的定制器,调用每一个定制器的customize方法来给Servlet容器进行属性赋值;
    for (EmbeddedServletContainerCustomizer customizer : getCustomizers()) {
        customizer.customize(bean);
    }
}

private Collection<EmbeddedServletContainerCustomizer> getCustomizers() {
    if (this.customizers == null) {
        // Look up does not include the parent context
        this.customizers = new ArrayList<EmbeddedServletContainerCustomizer>(
            this.beanFactory
            //从容器中获取所有这葛类型的组件:EmbeddedServletContainerCustomizer
            //定制Servlet容器,给容器中可以添加一个EmbeddedServletContainerCustomizer类型的组件
            .getBeansOfType(EmbeddedServletContainerCustomizer.class,
                            false, false)
            .values());
        Collections.sort(this.customizers, AnnotationAwareOrderComparator.INSTANCE);
        this.customizers = Collections.unmodifiableList(this.customizers);
    }
    return this.customizers;
}

  ServerProperties也是定制器

  步骤:

  1)、SpringBoot根据导入的依赖情况,给容器中添加相应的EmbeddedServletContainerFactory【TomcatEmbeddedServletContainerFactory】

  2)、容器中某个组件要创建对象就会惊动后置处理器;EmbeddedServletContainerCustomizerBeanPostProcessor;

  只要是嵌入式的Servlet容器工厂,后置处理器就工作;

  3)、后置处理器,从容器中获取所有的EmbeddedServletContainerCustomizer,调用定制器的定制方法

  嵌入式Servlet容器启动原理;

  什么时候创建嵌入式的Servlet容器工厂?什么时候获取嵌入式的Servlet容器并启动Tomcat;

  获取嵌入式的Servlet容器工厂:

  1)、SpringBoot应用启动运行run方法

  2)、refreshContext(context);SpringBoot刷新IOC容器【创建IOC容器对象,并初始化容器,创建容器中的每一个组件】;如果是web应用创建    AnnotationConfigEmbeddedWebApplicationContext,否则:AnnotationConfigApplicationContext

  3)、refresh(context);刷新刚才创建好的ioc容器;

public void refresh() throws BeansException, IllegalStateException {
   synchronized (this.startupShutdownMonitor) {
      // Prepare this context for refreshing.
      prepareRefresh();

      // Tell the subclass to refresh the internal bean factory.
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

      // Prepare the bean factory for use in this context.
      prepareBeanFactory(beanFactory);

      try {
         // Allows post-processing of the bean factory in context subclasses.
         postProcessBeanFactory(beanFactory);

         // Invoke factory processors registered as beans in the context.
         invokeBeanFactoryPostProcessors(beanFactory);

         // Register bean processors that intercept bean creation.
         registerBeanPostProcessors(beanFactory);

         // Initialize message source for this context.
         initMessageSource();

         // Initialize event multicaster for this context.
         initApplicationEventMulticaster();

         // Initialize other special beans in specific context subclasses.
         onRefresh();

         // Check for listener beans and register them.
         registerListeners();

         // Instantiate all remaining (non-lazy-init) singletons.
         finishBeanFactoryInitialization(beanFactory);

         // Last step: publish corresponding event.
         finishRefresh();
      }

      catch (BeansException ex) {
         if (logger.isWarnEnabled()) {
            logger.warn("Exception encountered during context initialization - " +
                  "cancelling refresh attempt: " + ex);
         }

         // Destroy already created singletons to avoid dangling resources.
         destroyBeans();

         // Reset 'active' flag.
         cancelRefresh(ex);

         // Propagate exception to caller.
         throw ex;
      }

      finally {
         // Reset common introspection caches in Spring's core, since we
         // might not ever need metadata for singleton beans anymore...
         resetCommonCaches();
      }
   }
}

  4)、 onRefresh(); web的ioc容器重写了onRefresh方法

  5)、webioc容器会创建嵌入式的Servlet容器;createEmbeddedServletContainer();

  6)、获取嵌入式的Servlet容器工厂:

  EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory();

  ​ 从ioc容器中获取EmbeddedServletContainerFactory 组件;TomcatEmbeddedServletContainerFactory创建对象,后置处理器一看是这个对象,就获取所有的定制器来先定制Servlet容器的相关配置;

  7)、使用容器工厂获取嵌入式的Servlet容器:this.embeddedServletContainer = containerFactory .getEmbeddedServletContainer(getSelfInitializer());

  8)、嵌入式的Servlet容器创建对象并启动Servlet容器;

  先启动嵌入式的Servlet容器,再将ioc容器中剩下没有创建出的对象获取出来;

  IOC容器启动创建嵌入式的Servlet容器


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