Java Web_web.xml配置404和500异常及错误

Java Web_web.xml配置404和500错误及异常
Web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
    http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
    <!-- 配置错误处理 -->
    <error-page>
       <error-code>404</error-code>
       <location>/404.html</location>
    </error-page>
    <error-page>
       <error-code>505</error-code>                            
       <location>/505.html</location>
    </error-page>
    <!-- 配置异常处理 -->
    <error-page>
       <exception-type>javax.servle.ServletException</exception-type>
       <location>/error.html</location>
    </error-page>
    <error-page>
       <exception-type>java.lang.NullPointerException</exception-type>
       <location>/error.html</location>
    </error-page>
</web-app>

异常：
当访问一个action或是servlet的时，可能会出现异常，
struts2中web.xml配置：
<default-action-ref name="pagenotfound"></default-action-ref>?
<action name="pagenotfound">
<result>/pagenotfound.html</result>?
</action>

servlet中web.xml配置：
    <error-page>
              <exception-type>javax.servle.ServletException</exception-type>
              <location>/error.html</location>
       </error-page>