-509 vs 510

我在使用 JDBC 时看到某种已更改或错误的数据。所以我观察使用H2数据库 http://h2database.com/Java 8 更新 151 上的版本 1.4.196。

这是一个完整的例子。

请注意我们如何检索日期值三次，第一次作为LocalDate对象，其次作为文本，第三作为int从演员表中提取的年份号LocalDate目的。在文本版本中我们可以看到年份确实是负数。神秘的是LocalDate有不同的年份数字，并且它是正数而不是负数。看起来像一个错误。

private void doIt ( )
{
    System.out.println( "BASIL - Running doIt." );
    try
    {
        Class.forName( "org.h2.Driver" );
    } catch ( ClassNotFoundException e )
    {
        e.printStackTrace( );
    }

    try (
            Connection conn = DriverManager.getConnection( "jdbc:h2:mem:" ) ;  // Unnamed throw-away in-memory database.
    )
    {
        conn.setAutoCommit( true );
        String sqlCreate = "CREATE TABLE history  ( id IDENTITY , when  DATE ); ";
        String sqlInsert = "INSERT INTO history ( when ) VALUES ( ? ) ; ";
        String sqlQueryAll = "SELECT * FROM history  ; ";

        PreparedStatement psCreate = conn.prepareStatement( sqlCreate );

        psCreate.executeUpdate( );

        PreparedStatement psInsert = conn.prepareStatement( sqlInsert );

        psInsert.setObject( 1 , LocalDate.of( 2017 , 1 , 23 ) );
        psInsert.executeUpdate( );

        psInsert.setObject( 1 , LocalDate.of( -509 , 1 , 1 ) );
        psInsert.executeUpdate( );

        PreparedStatement psQueryAll = conn.prepareStatement( sqlQueryAll );
        ResultSet rs = psQueryAll.executeQuery( );
        while ( rs.next( ) )
        {
            long l = rs.getLong( 1 );  // Identity column.
            // Retrieve the same date value in three different ways.
            LocalDate ld = rs.getObject( 2 , LocalDate.class );  // Extract a `LocalDate`, and implicitly call its `toString` method that uses standard ISO 8601 formatting.
            String s = rs.getString( 2 );  // Extract the date value as text from the database using the database-engine’s own formatting.
            int y = ( ( LocalDate ) rs.getObject( 2 , LocalDate.class ) ).getYear( );  // Extract the year number as an integer from a `LocalDate` object.
            String output = "ROW: " + l+ " | " + ld + " | when as String: " + s+ " | year: " + y ;
            System.out.println( output );
        }

        conn.close( );
    } catch ( SQLException e )
    {
        e.printStackTrace( );
    }
}

运行时。

行：1 | 2017-01-23 |当作为字符串时：2017-01-23 |年份: 2017

行：2 | 0510-01-01 |当作为字符串时：-509-01-01 |年份：510

所以似乎有一些与 JDBC 相关的事情正在发生。请注意年份是如何呈现为正 510 而不是负 509。我不理解这种行为。

我可以推断这是一个问题JDBC https://en.wikipedia.org/wiki/Java_Database_Connectivity而不是在内部LocalDate https://docs.oracle.com/javase/8/docs/api/java/time/LocalDate.html。看到这个在 IdeOne.com 中实时运行的示例代码 https://www.ideone.com/iVb7PW表明一个LocalDate对象确实携带并报告负年份。

LocalDate ld = LocalDate.of( -509 , 1 , 1 ) ;
System.out.println( "ld.toString(): " + ld ) ;
System.out.println( "ld.getYear(): " + ld.getYear() ) ;

注意我们是如何做的not处理时从 -509 转换为 510LocalDate仅，没有 JDBC。

LD：-0509-01-01

ld.getYear(): -509

我开了一个出票 https://github.com/h2database/h2database/issues/644关于H2项目。

The problem is caused by the conversion from java.sql.Date to LocalDate . Because it's a negative year, the Calendar instance holding the fetched result will transform the year to 1 - year but when converting to LocalDate java is not considering the additional information (era==BC) that indicates that the year < 0 The following is the final method executed before returning the result.

试试这个：

public class Test {
 public static void main(String[] args) {

            Calendar instance = Calendar.getInstance();
            instance.set(-509,1,1);

            java.sql.Date d = new Date(instance.getTime().getTime());

            System.out.println(d.toLocalDate().getYear());// 510


        }
}

谢谢 Ole V.V.征求您的意见！！！