Question

我有一个连接到数据库，执行sql查询并尝试将结果写入文件的函数。

public class DBReader {

    public ResultSet executeSQL(SqlContainer sc) {
        String url = "url";
        String user = "user";
        String password = "pw";
        Connection con;
        Statement stmt;
        ResultSet rs;

        try {
            System.out.println("=== Started SQL ===");
            Class.forName("com.ibm.db2.jcc.DB2Driver");
            con = DriverManager.getConnection(url, user, password);
            con.setAutoCommit(false);
            stmt = con.createStatement();

            rs = stmt.executeQuery(sc.getSQL());


            CSVWriter writer = new CSVWriter(new FileWriter("result.csv"));
            writer.writeAll(rs, true);

            stmt.close();
            con.commit();
            con.close();

            System.out.println("    Finished SQL");
            return rs;
        } catch (SQLException | ClassNotFoundException | IOException e) {
            e.printStackTrace();
        }
        return null;
    }

}

但是，当我执行上述功能时，出来的文件为空。我使用以下代码测试结果集是否为空，但是否执行：

while (rs.next()) {
                String value = rs.getString(4);
                System.out.println("Something = " + value);
            }

它返回一些值。

我要向任何方向的帮助或点头表示感谢，在此先感谢。

Answer 1

您也应该关闭writer：

writer.close();

或者更好的是，您可以使用try-with-resource语句自动关闭它：

        try(CSVWriter writer = new CSVWriter(new FileWriter("result.csv"));) {
            System.out.println("=== Started SQL ===");
            Class.forName("com.ibm.db2.jcc.DB2Driver");
            con = DriverManager.getConnection(url, user, password);
            con.setAutoCommit(false);
            stmt = con.createStatement();

            rs = stmt.executeQuery(sc.getSQL());

            writer.writeAll(rs, true);

            stmt.close();
            con.commit();
            con.close();

            System.out.println("    Finished SQL");
            return rs;
        } catch (SQLException | ClassNotFoundException | IOException e) {
            e.printStackTrace();
        }

将sql结果集写入CSV文件

1 个答案: