目录
- 1. 前言
- 2. 常用方法介绍
- 3. 代码演示
- 4. 结果图(一部分)
- 5. 源码
1. 前言
ResultSetMetaData 叫元数据,是数据库 列对象,以列为单位封装为对象。
元数据,指的是其包含列名,列值,列类型,列长度等等有用信息。
2. 常用方法介http://www.devze.com绍
ResultSetMetaData 常用方法:
1). metaData.getColumnName(i) 获取该列的原始名字
2). metaData.getColumnLabel(i) 获取该列的别名3). metaData.getColumnClassName(i) 获取该列的(在Java中的)数据类型4). metaData.getColumnType(i) 获取该列的(在数据库中的)数据类型对应的序号5). metaData.getColumnTypeName(i) 获取该列的(在数据库中的)数据类型6). metaData.getScale(i) 获取该列中小数点右边的位数7). metaData.getColumnDisplaySize(i) 获取该列的长度8). metaData.isAutoIncrement(i) 判断该列的值是否自动递增9). metaData.isNullable(i) 判断该列的值是否为null10). metaData.getTableName(i) 获取表名3python. 代码演示
先准备好一张表,如下图:
代码:
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 ResultSetMetaD编程客栈ata metaData = resultSet.getMetaData(); 编程客栈 // 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(); } }
4. 结果图(一部分)
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 getColumnT编程客栈ype(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
list:结果:
[{birthday=2021-02-27T17:47:08, address=北京, money=10.580, sex=男, id=41, username=老王}, {birthday=2021-03-02T15:09:37, address=北京, money=10.580, sex=女, id=42, username=小二王}, {birthday=2021-03-04T11:34:34, address=北京, money=10.580, sex=女, id=43, username=小二王}, {birthday=2021-03-04T12:04:06, address=北京, money=10.580, sex=男, id=45, username=大王}, {birthday=2021-03-07T17:37:26, address=北京, money=10.580, sex=男, id=46, username=老王}, {birthday=2021-03-08T11:开发者_C培训44, address=北京, money=10.580, sex=女, id=48, username=小马}, {birthday=null, address=null, money=null, sex=男, id=50, username=kkooop}]
5. 源码
https://gitee.com/Lgold/learning/tree/df1887c456aa4a140839104de0408f9dedb67ca4/src/main/java/com/king/learning/ResultSetMetaData
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