在spring boot中将所有mysql表数据转换成JSON

Question

我只想指定表名，它会自动将其所有数据转换为 JSON 格式

我已尝试使用 JDBC 将表中的数据存储到 JSON 中的代码。

public class DataBaseToJson {
    public static ResultSet RetrieveData() throws Exception {
        DriverManager.registerDriver(new com.mysql.jdbc.Driver());
        String mysqlUrl = "jdbc:mysql://localhost/studentsDB?autoReconnect=true&useSSL=false";
        Connection con = DriverManager.getConnection(mysqlUrl, "root", "root");
        Statement statement = con.createStatement();
        ResultSet resultSet = statement.executeQuery("Select * from students");
        return resultSet;
    }

    public static void main(String args[]) throws Exception {
        JSONObject jsonObject = new JSONObject();
        JSONArray array = new JSONArray();
        ResultSet resultSet = RetrieveData();
        while (resultSet.next()) {
            JSONObject record = new JSONObject();
            record.put("students ID", resultSet.getInt("students_id"));
            record.put("students Name", resultSet.getString("students_name"));
            array.add(record);
        }
        jsonObject.put("students Information", array);
        try {
            FileWriter file = new FileWriter("output.json");
            file.write(jsonObject.toJSONString());
            file.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

我不想在文件中指定文件。我想让它通用，这样我们就可以只输入表名，它会自动转换该表中的所有数据并保存到 JSON 文件中。

Answer 1

您可以使用INFORMATION_SCHEMA 为给定表选择列列表：

SELECT COLUMN_NAME FROM `INFORMATION_SCHEMA`.`COLUMNS` WHERE TABLE_NAME LIKE 'table_name'

现在，将上述查询中的ResultSet 转换为列名的List<String>。之后我们可以使用它来将最终的ResultSet 转换为JSON Object。

伪代码：

Connection connection = createConnection();
List<String> columns = loadColumns(connection, tableName);
ResultSet dataSet = loadData(connection, tableName);
while (dataSet.next()) {
    JSONObject record = new JSONObject();
    for (String column : columns) {
        record.put(column, dataSet.getObject(column));
    }
    array.add(record);
}
// save array to file

当ResultSet 很大时，我们应该考虑使用Jackson 或Gson 库中的Streaming API 以避免“内存不足”问题。

另见：

• How to get database structure in MySQL via query
• Jackson Streaming API
• Jackson - Processing model: Streaming API
• Gson Streaming

更新

看起来我们不需要使用额外的SQL 查询来选择列名，因为ResultSet 有getMetaData 方法：

检索此 ResultSet 对象的数量、类型和属性 列。

另见：

• ResultSetMetaData class

Answer 2

    public static void main(String args[]) throws Exception {
        String tableName = "books";
        Connection connection = createConnection();
        JSONArray array = new JSONArray();
        JSONObject jsonObject = new JSONObject();
        List<String> columns = loadColumns(connection, tableName);
        ResultSet dataSet = loadData(connection, tableName);
        while (dataSet.next()) {
            JSONObject record = new JSONObject();
            for (String column : columns) {
                record.put(column, dataSet.getObject(column));
            }
            array.add(record);
        }
        jsonObject.put(tableName, array);
        try {
            FileWriter file = new FileWriter("output.json");
            file.write(jsonObject.toJSONString());
            file.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static Connection createConnection() throws SQLException {
        DriverManager.registerDriver(new com.mysql.jdbc.Driver());
        String mysqlUrl = "jdbc:mysql://localhost/library?autoReconnect=true&useSSL=false";
        Connection connection = DriverManager.getConnection(mysqlUrl, "root", "root");
        return connection;
    }


    public static List<String> loadColumns(Connection connection, String tableName) throws SQLException {
        Statement statement = connection.createStatement();
        ResultSet resultSet = statement.executeQuery("SELECT COLUMN_NAME FROM `INFORMATION_SCHEMA`.`COLUMNS` WHERE TABLE_NAME LIKE '"+tableName+"'");
        List<String> columnsName = new ArrayList<String>();
        while(resultSet.next()) {
            columnsName.add(resultSet.getString("COLUMN_NAME"));
        }
        return columnsName;
    }

    public static ResultSet loadData(Connection connection, String tableName) throws SQLException {
        Statement statement = connection.createStatement();
        ResultSet resultSet = statement.executeQuery("Select * from "+tableName+"");
        return resultSet;
    }