SpringBoot嵌入式Servlet容器启动原理

我就是我 2022-03-10 12:44 228阅读 0赞

# 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）、执行refreshContext(context)方法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，否则创建AnnotationConfigApplicationContext

3）、执行refresh(context)方法，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）、执行onRefresh()方法， web的ioc容器重写了onRefresh方法；

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

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==\*\*