遍历结果集键 - 这可能吗？

Question

我有一个方法接受数据库连接、查询和参数，并将该查询解析为结果集对象。这很好，但问题是要从结果集中获取每个值，我必须为要提取的每一行数据编写一行代码，然后将其保存在 JSON 容器中。有没有办法系统地执行此操作，以便我可以自动解析数据类型并根据从结果集中获取的键创建 JSON 对象 w/o 手动指定键？

public static JSONArray q2rs2j(Connection connection, String query, List<String> params) throws Exception {
    JSONArray tContainer = new JSONArray();
    PreparedStatement pStatement = connection.prepareStatement(query);
    int pit = 1;
    if(params != null) {
        for (String param : params) {
            try {
                double paramAsDouble = Double.parseDouble(param);
                try {
                    int paramAsInt = Integer.parseInt(param);
                    pStatement.setInt(pit, paramAsInt);
                } catch (NumberFormatException e) {
                    pStatement.setDouble(pit, paramAsDouble);
                }
            } catch (NumberFormatException e) {
                pStatement.setString(pit, param);
            }
            pit++;
        }
    }
    ResultSet resultSet = pStatement.executeQuery();
    try {
        while (resultSet.next()) {
            // Iterate through KEYS in the resultSet.next() row
            while (hasKey) {
                // Store key Name and key Value in variables - todo: determine data type via try parsing as Int, double, etc
                String thisKeyName = (nextKeyName);
                String thisKeyValue = (nextKeyValue);
                JSONObject tObject = new JSONObject();
                tObject
                    .put(nextKeyName, nextKeyValue);
            }
            tContainer.put(tObject);
        }
        resultSet.close();
    } catch (Exception e) { e.printStackTrace(); }
    return tContainer;
}

Answer 1

ResultSetMetaData 提供 SQL 类型和 java class 名称。

try (ResultSet resultSet = pStatement.executeQuery()) {
    ResultSetMetaData meta = resultSet.getMetaData();
    int ncols = meta.getColumnCount();
    while (resultSet.next()) {
        JSONObject tObject = new JSONObject();
        for (int colno = 1; colno <= ncols; ++colno) {
            String label = meta.getColumnLabel(colno); // Key
            String name = meta.getColumnName(colno);
            String sqlType = meta.getColumnType();
            String type = meta.getColumnClassName();
            String thisKeyName = label;
            Object thisKeyValue = result.getObject(colno);
            if (sqlType.contains("CHAR")) {
                thisKeyVaule = result.getString(colno);
                tObject.put(nextKeyName, nextKeyValue);
            } else if (sqlType.contains("INT")) {
                thisKeyVaule = result.getInt(colno);
                tObject.put(nextKeyName, nextKeyValue);
            } else {
                tObject.put(nextKeyName, nextKeyValue);
            }
        }
        tContainer.put(tObject);
    }
}

使用 try-with-resources 允许自动关闭（对 Connection、Statement 和 ResultSet 有用）- 即使在 return、中断或抛出异常时也是如此。

遍历结果集键 - 这可能吗？

Iterate over result set keys - is it possible?

java

json

java-8

restlet