AbstractMemoryResultSet对SQL的wasNull实现有问题

[beefluga]

标志位wasNull是在结果集中某个字段的值是SQLNULL的时候会被设置为true，用来表示从ResultSet中获取的值是null。但是当某个字段的值不是null的时候应该及时修改此标志位。

但是AbstractMemoryResultSet的实现中没有及时修正此flag，导致查询的数据会出现一连串的null。

比如，getObject方法应该这样处理wasNull。

    @Override
    public Object getObject(final int columnIndex) throws SQLException {
        Preconditions.checkState(!isClosed(), "Result set is closed");
        Preconditions.checkState(!beforeFirst, "Before start of result set");
        Preconditions.checkState(null != currentRow, "After end of result set");
        Preconditions.checkArgument(currentRow.inRange(columnIndex), String.format("Column Index %d out of range", columnIndex));
        Object result = currentRow.getCell(columnIndex);
        wasNull = null == result;
        return result;
    }

当然还有其他的几个方法同样存在这样的问题。

Java中对此接口的定义如下：

    /**
     * Reports whether
     * the last column read had a value of SQL <code>NULL</code>.
     * Note that you must first call one of the getter methods
     * on a column to try to read its value and then call
     * the method <code>wasNull</code> to see if the value read was
     * SQL <code>NULL</code>.
     *
     * @return <code>true</code> if the last column value read was SQL
     *         <code>NULL</code> and <code>false</code> otherwise
     * @exception SQLException if a database access error occurs or this method is
     *            called on a closed result set
     */
    boolean wasNull() throws SQLException;