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