报错：java.lang.NoClassDefFoundError: Could not initialize class XXXX

用servet做的登陆注册的程序

，点击之后出现

下面是配置xml

    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_3_0.xsd">
 
    This is the description of my J2EE component
    This is the display name of my J2EE component
    UserLoginServlet
    com.bie.servlet.UserLoginServlet
 
 
    This is the description of my J2EE component
    This is the display name of my J2EE component
    UserRegisterServlet
    com.bie.servlet.UserRegisterServlet
 




 
    UserLoginServlet
    /userlogin
 
 
    UserRegisterServlet
    /userregister
 

好像是缺失类的问题，不过不知道怎么操作