resultSet 类型的方法

Question

public ResultSet Select(User usera){
PreparedStatement pst=null;
ResultSet rs=null;
UserCoon coon=new UserCoon();
Connection coona=coon.getCoon();
String sql_select="select * from user_table where id=?";
try {
pst=coona.prepareStatement(sql_select);
pst.setString(1,usera.getId());
rs=pst.executeQuery();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return rs;
}
<%

request.setCharacterEncoding("utf-8");
UserDao user=new UserDao();//实例化
User usera=new User();
usera.setId(request.getParameter("id"));
ResultSet rsts=user.Select(usera);

%>

" method="post">
用户名：">

密 码：">

用户类型：

rsts.getString(）；这部分报错，为什么呀。方法里无参的时候可正常执行

Answer 1

因为没有查找到匹配的数据