基于数据库的java登录验证

Question

当输入的用户存在于数据库中时，resultset的if部分会运行，但当它不存在时，else部分不会运行。为什么

这是我的密码

String thisname=request.getParameter("username");
String thispwd=request.getParameter("password");

//Query for selecting user name and password from database.
String query = "select * from login where username=?";
pstmt = (PreparedStatement) con.prepareStatement(query);
pstmt.setString(1, thisname);
res = pstmt.executeQuery();

while(res.next())
{
    System.out.println("hhh");

    if ((thisname.equals(res.getString("username"))) && (thispwd.equals(res.getString("password"))))
    {
        System.out.println("hello");                                            
    }               
    else
    {
        System.out.println("in");
        session.invalidate();
        response.sendRedirect("index.html");
    }    
}