Why mybatis insert java.util.Date value to Mysql datetime column then fetch it they are not equal?

问题

Mybatis insert java.util.Date to mysql datetime column, then fetch it find they are not match

Table

CREATE TABLE `t` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`create_time` datetime DEFAULT NULL,
 PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8

code

@Insert("insert into t(create_time) values(#{0})")
int insertT(Date date);
@Select("select create_time from t order by id desc limit 1")
Date getLatestCreateTime();

Unit test

    Date date1 = new Date();
    mapper.insertT(date1);

    Date date2 = mapper.getLatestCreateTime();

    Assert.assertEquals(date1, date2);

Assert fail

java.lang.AssertionError: 
Expected :Tue Aug 02 22:10:35 CST 2016
Actual   :Tue Aug 02 22:10:36 CST 2016

why is so?

回答1:

because when TimeUtil in mysql-connector convert Timstamp to Date, it executes below code

    Timestamp ts = new Timestamp(tsAsMillis1 + (long)offsetDiff);
    ts.setNanos(secondsPart);

and secondsPart is 0.

@Test
public void test_date_compare_date_from_timestamp() {
    Date date1 = new Date();

    Timestamp ts = new Timestamp(date1.getTime());
    System.out.println(ts);  // 2016-08-08 22:37:37.078
    Date date2 = new Date(ts.getTime());
    Assert.assertEquals(date1, date2);
    ts.setNanos(0);
    System.out.println(ts); // 2016-08-08 22:37:37.0
    Date date3 = new Date(ts.getTime());
    Assert.assertNotEquals(date1, date3);
}

and as for the seconds is more then original seconds, it is because

insert into t select 1,'2016-08-08 22:42:44.676';
select * from t;
+----+---------------------+
| id | create_time         |
+----+---------------------+
|  1 | 2016-08-08 22:42:45 |
+----+---------------------+

来源：https://stackoverflow.com/questions/38722942/why-mybatis-insert-java-util-date-value-to-mysql-datetime-column-then-fetch-it-t

标签

datetime

MyBatis

mysql-connector