servlet 查询list结果重复

正确代码： 

        String sql= "select * from test_user";
        Connection conn= dbutil.getCon();
        List<TestUser> list=new ArrayList<TestUser>();
        try {
            PreparedStatement ps = conn.prepareStatement(sql);
            ResultSet set = ps.executeQuery();
            while (set.next()){

                //这里
                TestUser user=new TestUser();
                user.setUid(set.getString("U_ID"));
                user.setUname(set.getString("U_NAME"));
                list.add(user);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            dbutil.closeCon(conn);
            return list;
        }

错误代码：

 String sql= "select * from test_user";
        Connection conn= dbutil.getCon();
        List<