每次输入后都显示用户名和密码不能为空，然后密码输入错误了，他显示无此用户。顺序问题？

<%@ page contentType="text/html;charset=gb2312"%>
<%@ page import="java.util.HashMap"%>
<%@ page import="java.util.Map"%>
<%@ page import="noc.oa.dto.*"%>
<%@ page import="noc.common.base.Dao"%>
<%
String User = request.getParameter("User"); //得到登录用户名
String Pwd = request.getParameter("Pwd"); //得到登录密码
if (null == User || "".equals(User) || null == Pwd
|| "".equals(Pwd));
System.out.println("用户名和密码不能为空");

System.out.println(User);/* 输出用户名和密码 */
System.out.println(Pwd);
Dao dao = new Dao();
dao.startTransaction();
try {
Map<String, Object> param = new HashMap<String, Object>();
param.put("login_name", User);
param.put("passwd", Pwd);
Person person = (Person) dao.select(
"PersonMapper.selectPersonByUsernamePassword", param);
if (person == null) {
System.out.println("无此用户");
}
else if(!person.getPasswd().equals(Pwd)){
System.out.println("密码错误");
}
else {
System.out.println("用户校验正确");
}
} finally {
dao.endTransaction();
}
%>

相关了解……