spring boot 如何启动tomcat（传统tomcat启动服务与springboot启动内置tomcat服务的区别推荐）

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns="http://java.sun.com/xml/ns/javaee"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
                             http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>Archetype Created Web Application</display-name>
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
  <!-- 加载spring容器 -->
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:spring/applicationContext-*.xml</param-value>
  </context-param>
​
  <servlet>
    <servlet-name>mvc-dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <!-- 配置springMVC需要加载的配置文件-->
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath:spring/spring-*.xml</param-value>
    </init-param>
  </servlet>
​
  <servlet-mapping>
    <servlet-name>mvc-dispatcher</servlet-name>
    <!-- 默认匹配所有的请求 -->
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>

public final void init() throws ServletException {
		// Set bean properties from init parameters.
		PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
		if (!pvs.isEmpty()) {
			try {
				BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
				ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
				bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
				initBeanWrapper(bw);
				bw.setPropertyValues(pvs, true);
			}
			catch (BeansException ex) {
				if (logger.isErrorEnabled()) {
					logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
				}
				throw ex;
			}
		}

        // 最后会调用org.springframework.context.ConfigurableApplicationContext#refresh容器的刷新方法，
        // 进行springmvc容器初始化
		initServletBean();
	}
    }

// spring中的BeanDefinitionRegistryPostProcessor是BeanFactoryPostProcessor的子接口，
// BeanFactoryPostProcessor的作用是在bean的定义信息已经加载但还没有初始化的时候执行方法postProcessBeanFactory(）方法，
// 而BeanDefinitionRegistryPostProcessor是在BeanFactoryPostProcessor的前面执行，在源码
// org.springframework.context.support.PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors()方法里面定义了执行顺序
// BeanFactoryPostProcessor是bean工厂的bean属性处理容器，说通俗一些就是可以管理我们的bean工厂内所有的beandefinition（未实例化）数据，可以随心所欲的修改属性。
public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            prepareRefresh();
            
            //获取告诉子类初始化Bean工厂 将bean加载到缓存中 spring springmvc整合是在这初始化bean的
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
            
            prepareBeanFactory(beanFactory);
​
            try {
                postProcessBeanFactory(beanFactory);
​
                // springboot容器启动加载到这时，初始化了下面几个bean name
                //0 = "org.springframework.context.annotation.internalConfigurationAnnotationProcessor" =》对应ConfigurationClassPostProcessor类
                //1 = "org.springframework.context.annotation.internalAutowiredAnnotationProcessor" =》 AutowiredAnnotationBeanPostProcessor
                //2 = "org.springframework.context.annotation.internalCommonAnnotationProcessor" =》 CommonAnnotationBeanPostProcessor
                //3 = "org.springframework.context.event.internalEventListenerProcessor" =》 EventListenerMethodProcessor
                //4 = "org.springframework.context.event.internalEventListenerFactory" =》 DefaultEventListenerFactory
                // 调用我们的bean工厂的后置处理器.加载bean定义（不是实例化）,通过ConfigurationClassPostProcessor去加载启动类中的扫描路径
                // 然后将路径下到bean加载进来
                invokeBeanFactoryPostProcessors(beanFactory);
​
                registerBeanPostProcessors(beanFactory);
​
                initMessageSource();
​
                initApplicationEventMulticaster();
​
                // 这个方法同样也是留个子类实现的springboot也是从这个方法进行启动tomat的.
                onRefresh();
​
                registerListeners();
​
                //实例化我们剩余的单实例bean.
                finishBeanFactoryInitialization(beanFactory);
​
                // 最后容器刷新 发布刷新事件(Spring cloud也是从这里启动的)
                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();
            }
        }
    }