O preço do aprendizado é alto, mas não desisto - Erro 404

<?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" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>FJ21-Agenda</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
    <welcome-file>adiciona-contato.html</welcome-file>
    <!--  <welcome-file>404.html</welcome-file>-->
    <welcome-file>bemvindo.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>servletOiMundo</servlet-name>
    <servlet-class>br.com.caelum.servlet.OiMundo</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>servletOiMundo</servlet-name>
    <url-pattern>/oi</url-pattern>
  </servlet-mapping>
  <servlet>
    <servlet-name>AdicionaContato</servlet-name>
    <servlet-class>br.com.caelum.agenda.servlet.AdicionaContatoServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>AdicionaContato</servlet-name>
    <url-pattern>/adicionaContato</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>ControllerServlet</display-name>
    <servlet-name>ControllerServlet</servlet-name>
    <servlet-class>br.com.caelum.mvc.servlet.ControllerServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ControllerServlet</servlet-name>
    <url-pattern>/ControllerServlet</url-pattern>
  </servlet-mapping>
  <servlet>
  <servlet-name>controlador</servlet-name>
    <servlet-class>br.com.caelum.mvc.servlet.ControllerServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>controlador</servlet-name>
    <url-pattern>/mvc</url-pattern>
  </servlet-mapping>
  
  <filter>
    <filter-name>struts2</filter-name>
    <filter-class>
        org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter
    </filter-class>
  </filter>
  <filter-mapping>
    <filter-name>struts2</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  
</web-app>