一、初始化过程图
上图展示了web容器初始化的过程，其官方文档给出了这样的描述：
When a web application is deployed into a container, the following steps must be performed, in this order, before the web application begins processing client requests.
- Instantiate an instance of each event listener identified by a <listener> element in the deployment descriptor.
- For instantiated listener instances that implement ServletContextListener, call the contextInitialized() method.
- Instantiate an instance of each filter identified by a <filter> element in the deployment descriptor and call each filter instance's init() method.
- Instantiate an instance of each servlet identified by a <servlet> element that includes a <load-on-startup> element in the order defined by the load-on-startup element values, and call each servlet instance's init() method.
二、web.xml的配置
1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 3 xmlns="http://java.sun.com/xml/ns/javaee" 4 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" 5 id="WebApp_ID" version="3.0"> 6 <display-name>test-springmvc</display-name> 7 8 <!-- 指定Spring Bean的配置文件所在目录。默认配置在WEB-INF目录下 --> 9 <context-param> 10 <param-name>contextConfigLocation</param-name> 11 <param-value>classpath:spring/spring-context.xml</param-value> 12 </context-param> 13 14 <!-- Spring监听器 --> 15 <listener> 16 <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> 17 </listener> 18 19 <!-- 中文过滤器 --> 20 <filter> 21 <filter-name>CharacterEncodingFilter</filter-name> 22 <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class> 23 <init-param> 24 <param-name>encoding</param-name> 25 <param-value>UTF-8</param-value> 26 </init-param> 27 <init-param> 28 <param-name>forceEncoding</param-name> 29 <param-value>true</param-value> 30 </init-param> 31 </filter> 32 <filter-mapping> 33 <filter-name>CharacterEncodingFilter</filter-name> 34 <url-pattern>/*</url-pattern> 35 </filter-mapping> 36 37 <!-- Spring MVC配置 --> 38 <servlet> 39 <servlet-name>spring</servlet-name> 40 <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> 41 <!-- 可以自定义servlet.xml配置文件的位置和名称，默认为WEB-INF目录下，名称为[<servlet-name>]-servlet.xml，如spring-servlet.xml --> 42 <init-param> 43 <param-name>contextConfigLocation</param-name> 44 <param-value>classpath:spring/spring-mvc.xml</param-value> 45 </init-param> 46 <load-on-startup>1</load-on-startup> 47 </servlet> 48 49 <servlet-mapping> 50 <servlet-name>spring</servlet-name> 51 <url-pattern>/</url-pattern> 52 </servlet-mapping> 53 54 55 56 <welcome-file-list> 57 <welcome-file>index.jsp</welcome-file> 58 </welcome-file-list> 59 </web-app>
上是截取的web.xml中的配置，在<listener>标签中定义了spring容器加载监听器；在<filter>标签中定义了过滤器；在<servlet>标签中定义了spring前端控制器。
三、启动源码分析
可以在Web项目启动过程中，进行调试，得到以下启动步骤
由上可知初始化顺序：监听器 -> 过滤器 -> Servlet
参考：https://www.cnblogs.com/RunForLove/p/5688731.html
