项目中遇到存储的时间戳与真实时间相差14小时的现象,以下为解决步骤.
问题
CREATE TABLE `incident` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`created_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
`recovery_time` timestamp NULL DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=0 DEFAULT CHARSET=utf8mb4;
以上为数据库建表语句,其中created_time是插入记录时自动设置,recovery_time需要手动进行设置.
测试时发现,created_time为正确的北京时间,然而recovery_time则与设置时间相差14小时.
尝试措施
jvm时区设置
//设置jvm默认时间
System.setProperty("user.timezone", "UTC");
数据库时区查询
查看数据库时区设置:
show variables like '%time_zone%';
--- 查询结果如下所示:
--- system_time_zone: CST
--- time_zone:SYSTEM
查询CST发现其指代比较混乱,有四种含义(参考网址:https://juejin.im/post/5902e087da2f60005df05c3d):
美国中部时间 Central Standard Time (USA) UTC-06:00
澳大利亚中部时间 Central Standard Time (Australia) UTC+09:30
中国标准时 China Standard Time UTC+08:00
古巴标准时 Cuba Standard Time UTC-04:00
此处发现如果按照美国中部时间进行推算,相差14小时,与Bug吻合.
验证过程
MyBatis转换
代码中,时间戳使用Instant进行存储,因此跟踪package org.apache.ibatis.type下的InstantTypeHandler.
@UsesJava8
public class InstantTypeHandler extends BaseTypeHandler {
@Override
public void setNonNullParameter(PreparedStatement ps, int i, Instant parameter, JdbcType jdbcType) throws SQLException {
ps.setTimestamp(i, Timestamp.from(parameter));
}
//...代码shenglve
}
调试时发现parameter为正确的UTC时.
函数中调用Timestamp.from将Instant转换为Timestamp实例,检查无误.
/**
* Sets the designated parameter to the given java.sql.Timestamp value.
* The driver
* converts this to an SQL TIMESTAMP value when it sends it to the
* database.
*
* @param parameterIndex the first parameter is 1, the second is 2, ...
* @param x the parameter value
* @exception SQLException if parameterIndex does not correspond to a parameter
* marker in the SQL statement; if a database access error occurs or
* this method is called on a closed PreparedStatement */
void setTimestamp(int parameterIndex, java.sql.Timestamp x)
throws SQLException;
继续跟踪setTimestamp接口,其具体解释见代码注释.
Sql Driver转换
项目使用com.mysql.cj.jdbc驱动,跟踪其setTimestamp在ClientPreparedStatement类下的具体实现(PreparedStatementWrapper类下实现未进入).
@Override
public void setTimestamp(int parameterIndex, Timestamp x) throws java.sql.SQLException {
synchronized (checkClosed().getConnectionMutex()) {
((PreparedQuery>) this.query).getQueryBindings().setTimestamp(getCoreParameterIndex(parameterIndex), x);
}
}
继续跟踪上端代码中的getQueryBindings().setTimestamp()实现(com.mysql.cj.ClientPreparedQueryBindings).
@Override
public void setTimestamp(int parameterIndex, Timestamp x, Calendar targetCalendar, int fractionalLength) {
if (x == null) {
setNull(parameterIndex);
} else {
x = (Timestamp) x.clone();
if (!this.session.getServerSession().getCapabilities().serverSupportsFracSecs()
|| !this.sendFractionalSeconds.getValue() && fractionalLength == 0) {
x = TimeUtil.truncateFractionalSeconds(x);
}
if (fractionalLength < 0) {
// default to 6 fractional positions
fractionalLength = 6;
}
x = TimeUtil.adjustTimestampNanosPrecision(x, fractionalLength, !this.session.getServerSession().isServerTruncatesFracSecs());
//注意此处时区转换
this.tsdf = TimeUtil.getSimpleDateFormat(this.tsdf, "''yyyy-MM-dd HH:mm:ss", targetCalendar,
targetCalendar != null ? null : this.session.getServerSession().getDefaultTimeZone());
StringBuffer buf = new StringBuffer();
buf.append(this.tsdf.format(x));
if (this.session.getServerSession().getCapabilities().serverSupportsFracSecs()) {
buf.append('.');
buf.append(TimeUtil.formatNanos(x.getNanos(), 6));
}
buf.append(''');
setValue(parameterIndex, buf.toString(), MysqlType.TIMESTAMP);
}
}
注意此处时区转换,会调用如下语句获取默认时区:
this.session.getServerSession().getDefaultTimeZone()
获取TimeZone数据,具体如下图所示:
检查TimeZone类中offset含义,具体如下所示:
/**
* Gets the time zone offset, for current date, modified in case of
* daylight savings. This is the offset to add to UTC to get local time.
*
* This method returns a historically correct offset if an
* underlying TimeZone implementation subclass
* supports historical Daylight Saving Time schedule and GMT
* offset changes.
*
* @param era the era of the given date.
* @param year the year in the given date.
* @param month the month in the given date.
* Month is 0-based. e.g., 0 for January.
* @param day the day-in-month of the given date.
* @param dayOfWeek the day-of-week of the given date.
* @param milliseconds the milliseconds in day in standard
* local time.
*
* @return the offset in milliseconds to add to GMT to get local time.
*
* @see Calendar#ZONE_OFFSET
* @see Calendar#DST_OFFSET
*/
public abstract int getOffset(int era, int year, int month, int day,
int dayOfWeek, int milliseconds);
offset表示本地时间与UTC时的时间间隔(ms).
计算数值offset,发现其表示美国中部时间,即UTC-06:00.
Driver推断Session时区为UTC-6;
Driver将Timestamp转换为UTC-6的String;
MySql认为Session时区在UTC+8,将String转换为UTC+8.
因此,最终结果相差14小时,bug源头找到.
解决方案
参照https://juejin.im/post/5902e087da2f60005df05c3d.
mysql> set global time_zone = '+08:00';
Query OK, 0 rows affected (0.00 sec)
mysql> set time_zone = '+08:00';
Query OK, 0 rows affected (0.00 sec)
告知运维设置时区,重启MySql服务,问题解决.
此外,作为防御措施,可以在jdbc url中设置时区(如此设置可以不用修改MySql配置):
jdbc:mysql://localhost:3306/table_name?useTimezone=true&serverTimezone=GMT%2B8
此时,就告知连接进行时区转换,并且时区为UTC+8.
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