Question

我有一个sql查询要在我的java类（Servlet）中运行，如果该查询的数据库中没有数据，那么我想做的事情。

简单来说，我正在检查结果集中是否有没有想要做其他事情的数据，但这不起作用

我尝试过的事情

String str = null;
    Gson gson = new Gson();
    LinkedHashMap<Object, Object> lhm = null;
    LinkedList<LinkedHashMap<Object, Object>> mainList = new LinkedList<LinkedHashMap<Object, Object>>();

    String sql;

    try {
        Connection con = DBConnection.createConnection();
        Statement statement = con.createStatement();

        sql = "select distinct a.DISPLAYCOUNTERNAME from DISPLAYCOUNTERNAMES a,DISPLAYCOUNTER b where a.DISPLAYCOUNTERCODE=b.DISPLAYCOUNTERCODE and USERNAME='"
                + userName + "'";

        System.out.println(sql);
        ResultSet resultSet = statement.executeQuery(sql);

        if (!resultSet.isBeforeFirst()) { // if there is no data
            lhm = new LinkedHashMap<Object, Object>();
            lhm.put("outlet", "NoData");
            mainList.add(lhm);
            str = gson.toJson(mainList);
        }

            while (resultSet.next()) { // if there is data
                lhm = new LinkedHashMap<Object, Object>();
                counterName = resultSet.getString("DISPLAYCOUNTERNAME");
                 System.out.println("counternam"+counterName);
                lhm.put("Counter name", counterName);

                mainList.add(lhm);
                str = gson.toJson(mainList);

            }


        System.out.println(str);
        response.setContentType("application/json");
        response.getWriter().write(str);

    } catch (SQLException e) {
        System.out.println("SQL Issues 2...");
        e.printStackTrace();
    }

上面的代码以SQL Issues 2... java.sql.SQLException: This method should only be called on ResultSet objects that are scrollable (type TYPE_SCROLL_INSENSITIVE).的形式抛出错误

我不知道我在这里做错了什么，我们将不胜感激

Answer 1

您可以尝试修改该行：

Statement statement = con.createStatement();

到

Statement statement = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, 
                                          ResultSet.CONCUR_READ_ONLY);

Answer 2

您可以使用next，但切换为使用do / while循环，如果对next的第一次调用返回true，则行指针指向结果集中的第一行，因此您必须阅读在再次调用next之前

if (!resultSet.next()) { 
   // do no data stuff
} else { 
    do { 
      //handle result set data
    } while (rs.next()); 
}

如何在Java中检查结果集为空或为空

2 个答案: