web.xml是Schema约束的

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://www.example.org/web-app_2_5" 
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://www.example.org/web-app_2_5 web-app_2_5.xsd"
            version="2.5">
    <servlet>
        <servlet-name>MyServlet1</servlet-name>
        <servlet-class>demo1.person</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>MyServlet1</servlet-name>
        <url-pattern>/hello</url-pattern>
    </servlet-mapping>
</web-app>

servlet-class是路径（包名+类名）