晕~~~~为什么这个collection的值输不出来!~~~~

在servlet的部分代码如下：
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException,IOException{
response.setContentType(CONTENT_TYPE);
Collection ret=new ArrayList();
try{
Statement stm=conn.createStatement();
ResultSet rs=stm.executeQuery("select count(*) from work_admin");
int message_count=0;
if(rs.next())
{
message_count=rs.getInt(1);
rs.close();
}
if(message_count>0)
{
rs=stm.executeQuery("select * from work_admin order by CreateTime desc");
while(rs.next())
{
int ID=rs.getInt("Admin_id");
String username=rs.getString("username");
String password=rs.getString("password");
String Email=rs.getString("Email");
String Telephone=rs.getString("Telephone");
java.sql.Date CreateTime=rs.getDate("CreateTime");
java.sql.Date LastLoginTime=rs.getDate("LastLoginTime");
String IP=rs.getString("LastLoginIP");
UserAdd message=new UserAdd();
message.setID(ID);
message.setUsername(username);
message.setPassword(password);
message.setEmail(Email);
message.setTelephone(Telephone);
message.getCreateTime(CreateTime);
message.getLastLoginTime(LastLoginTime);
message.setIP(IP);
ret.add(message);
}
rs.close();
stm.close();
}
request.setAttribute("UserLists",ret);
request.getRequestDispatcher("/jsp_bin/User_Manage.jsp").forward(request,response);
}
catch(Exception e)
{
e.printStackTrace();
}
}
在User_Manage.jsp代码如下：
Collection userlist=(Collection)request.getAttribute("UserLists");
out.print(userlist);///---->这里输出来是null值？？？？？
Iterator it=userlist.iterator();
while(it.hasNext()){
UserAdd list=(UserAdd)it.next();
}