cannot be cast to org.springframework.security.userdetails.UserDetails

异常描述：java.lang.ClassCastException: xxx.xxx.xxx cannot be cast to org.springframework.security.userdetails.UserDetails

异常原因：SpringSecurity 3.0中自定义UserDetailService时因为模型对象未实现UserDetails 接口，导到模型对象向上转型时发生转化异常。

异常解决：将xxx.xxx.xxx实现UserDetails接口。