Java中ResultSetMetaData 元数据的具体使用

public class Test {

    private static final String URL = "jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC&useUnicode=true&characterEncoding=utf8";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "root";

    public static void main(String[] args) throws Exception {
        Class.forName("com.mysql.cj.jdbc.Driver");
        Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
        // sql 语句 是使用了 别名的
        PreparedStatement preparedStatement = connection.prepareStatement("select id as ID, username as USERNAME, birthday as BIRTHDAY, sex as SEX, address as ADDRESS, money as MONEY  from user ");
        ResultSet resultSet = preparedStatement.executeQuery();
        // 获取元数据对象
        ResultSetMetaData metaData = resultSet.getMetaData();
        // 获取一共有多少列
        int columnCount = metaData.getColumnCount();
        // 将数据封装为Map
        List<Map<String, Object>> list = new ArrayList<>();
        while (resultSet.next()) {
            Map<String, Object> columnMap = new HashMap<>();
            // 注：列名的索引 起始是 1 不是 0
            for (int i = 1; i <= columnCount; i++) {
                System.out.println("getColumnName(i): " + metaData.getColumnName(i));
                System.out.println("getColumnLabel(i): " + metaData.getColumnLabel(i));
                System.out.println("getColumnClassName(i): " + metaData.getColumnClassName(i));
                System.out.println("getColumnType(i): " + metaData.getColumnType(i));
                System.out.println("getColumnTypeName(i): " + metaData.getColumnTypeName(i));
                System.out.println("getScale(i): " + metaData.getScale(i));
                System.out.println("isNullable(i): " + metaData.isNullable(i));
                System.out.println("isAutoIncrement(i): " + metaData.isAutoIncrement(i));
                System.out.println("getTableName(i): " + metaData.getTableName(i));
                System.out.println();

                String key = metaData.getColumnName(i);
                Object value = resultSet.getObject(key);
                columnMap.put(key, value);
            }
            list.add(columnMap);
        }
        System.out.println();
        System.out.println(list);
        resultSet.close();
        preparedStatement.close();
        connection.close();
    }
}

getColumnName(i): id
getColumnLabel(i): ID
getColumnClassName(i): java.lang.Integer
getColumnType(i): 4
getColumnTypeName(i): INT
getScale(i): 0
isNullable(i): 0
isAutoIncrement(i): true   // id 自增 因此为true
getTableName(i): user

getColumnName(i): username
getColumnLabel(i): USERNAME
getColumnClassName(i): java.lang.String
getColumnType(i): 12
getColumnTypeName(i): VARCHAR
getScale(i): 0
isNullable(i): 0
isAutoIncrement(i): false
getTableName(i): user

getColumnName(i): birthday
getColumnLabel(i): BIRTHDAY
getColumnClassName(i): java.time.LocalDateTime
getColumnType(i): 93
getColumnTypeName(i): DATETIME
getScale(i): 0
isNullable(i): 1
isAutoIncrement(i): false
getTableName(i): user

getColumnName(i): sex
getColumnLabel(i): SEX
getColumnClassName(i): java.lang.String
getColumnType(i): 1
getColumnTypeName(i): CHAR
getScale(i): 0
isNullable(i): 1
isAutoIncrement(i): false
getTableName(i): user

getColumnName(i): address
getColumnLabel(i): ADDRESS
getColumnClassName(i): java.lang.String
getColumnType(i): 12
getColumnTypeName(i): VARCHAR
getScale(i): 0
isNullable(i): 1
isAutoIncrement(i): false
getTableName(i): user

getColumnName(i): money
getColumnLabel(i): MONEY
getColumnClassName(i): java.math.BigDecimal
getColumnType(i): 3
getColumnTypeName(i): DECIMAL
getScale(i): 3     // 在数据库中该列值是 decimal 且是3位小数 因此得出 3
isNullable(i): 1
isAutoIncrement(i): false
getTableName(i): user