Java 中的 Mysql 时区问题
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话说工作十多年,mysql 还真没用几年。起初是外企银行,无法直接接触到 DB;后来一直从事架构方面,也多是解决问题为主。
这次搭建海外机房,围绕时区大家做了一番讨论。不说最终的结果是什么,期间有同事认为 DB 返回的是 UTC 时间。
这里简单做个验证,顺便看下时区的问题到底是如何处理。
环境
openjdk version “1.8.0_242” mysql-connector-java “8.0.20” mysql “5.7” 时区 TZ=Europe/London 本地时区 GMT+8
创建个简单的库test
及表user
, 表结构如下:
CREATE TABLE `user` (
`name` varchar(50) NOT NULL,
`birth_date` timestamp NULL DEFAULT CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=latin1
插入一条测试数据:
mysql> insert into `user`
-> values ('Tom', time('2020-05-15 08:00:00'));
Query OK, 1 row affected (0.01 sec)
mysql> select * from user;
+------+---------------------+
| name | birth_date |
+------+---------------------+
| Tom | 2020-05-14 08:00:00 |
+------+---------------------+
1 row in set (0.00 sec)
测试代码:
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test?useSSL=false", "root", "root");
Statement stmt = conn.createStatement();
stmt.execute("select * from user where name = 'Tom'");
ResultSet rs = stmt.getResultSet();
while (rs.next()) {
Timestamp timestamp = rs.getTimestamp("birth_date");
System.out.println(timestamp.toLocalDateTime().toString());
}
执行结果:
2020-05-14T15:00
分析
程序的执行过程同时用 wireshark 抓了包。可以看到一次查询,做了这么多次的交互(包含了会话初始化)。这里可以看到 #177 的交互返回查询的结果:Tom 2020-05-14 08:00:00
,与 DB 中的数据相符。可见,返回的并不是 UTC 时间。
在 TCP 抓包结果中 #155 的查询语句:
/* mysql-connector-java-8.0.20 (Revision: afc0a13cd3c5a0bf57eaa809ee0ee6df1fd5ac9b) */
SELECT @@session.auto_increment_increment AS auto_increment_increment,
@@character_set_client AS character_set_client,
@@character_set_connection AS character_set_connection,
@@character_set_results AS character_set_results,
@@character_set_server AS character_set_server,
@@collation_server AS collation_server,
@@collation_connection AS collation_connection,
@@init_connect AS init_connect,
@@interactive_timeout AS interactive_timeout,
@@license AS license,
@@lower_case_table_names AS lower_case_table_names,
@@max_allowed_packet AS max_allowed_packet,
@@net_write_timeout AS net_write_timeout,
@@performance_schema AS performance_schema,
@@query_cache_size AS query_cache_size,
@@query_cache_type AS query_cache_type,
@@sql_mode AS sql_mode,
@@system_time_zone AS system_time_zone,
@@time_zone AS time_zone,
@@transaction_isolation AS transaction_isolation,
@@wait_timeout AS wait_timeout;
服务端返回的 time_zone
为 BST
。与本地时区的转换,由 mysql 的 connector 自动完成。
进阶
时区自动转换
实现源码:
ResultSetImpl
源码
this.defaultTimestampValueFactory = new SqlTimestampValueFactory(pset, null, this.session.getServerSession().getServerTimeZone());
@Override
public Timestamp getTimestamp(int columnIndex) throws SQLException {
checkRowPos();
checkColumnBounds(columnIndex);
return this.thisRow.getValue(columnIndex - 1, this.defaultTimestampValueFactory);
}
如何确认服务端时区?
使用会话中的服务端时区进行服务端时区。会话初始化时会进行时区的确认,比如前面获取的到BST
。确认时区的逻辑在NativeProtocol#configureTimezone()
中:
public void configureTimezone() {
#从mysql的响应获取 time_zone 和 system_time_zone 的设置
String configuredTimeZoneOnServer = this.serverSession.getServerVariable("time_zone");
if ("SYSTEM".equalsIgnoreCase(configuredTimeZoneOnServer)) {
configuredTimeZoneOnServer = this.serverSession.getServerVariable("system_time_zone");
}
#从 jdbc url 参数 serverTimezone 获取时区
String canonicalTimezone = getPropertySet().getStringProperty(PropertyKey.serverTimezone).getValue();
if (configuredTimeZoneOnServer != null) {
//如果 jdbc url 中未通过 serverTimezone 指定时区。则从TimeZoneMapping.properties中获取mysql 回传的时区缩写对应的标准时区,比如此处的 BST => Europe/London
//会出现无法映射的情况,不如 CEST 无法映射到 => Europe/Berlin,可以指定自定义的 Properties 文件进行映射
// user can override this with driver properties, so don't detect if that's the case
if (canonicalTimezone == null || StringUtils.isEmptyOrWhitespaceOnly(canonicalTimezone)) {
try {
canonicalTimezone = TimeUtil.getCanonicalTimezone(configuredTimeZoneOnServer, getExceptionInterceptor());
} catch (IllegalArgumentException iae) {
throw ExceptionFactory.createException(WrongArgumentException.class, iae.getMessage(), getExceptionInterceptor());
}
}
}
//如果 jdbc url 中通过 serverTimezone 指定了时区,则优先使用该时区
if (canonicalTimezone != null && canonicalTimezone.length() > 0) {
this.serverSession.setServerTimeZone(TimeZone.getTimeZone(canonicalTimezone));
//
// The Calendar class has the behavior of mapping unknown timezones to 'GMT' instead of throwing an exception, so we must check for this...
//
if (!canonicalTimezone.equalsIgnoreCase("GMT") && this.serverSession.getServerTimeZone().getID().equals("GMT")) {
throw ExceptionFactory.createException(WrongArgumentException.class, Messages.getString("Connection.9", new Object[] { canonicalTimezone }),
getExceptionInterceptor());
}
}
}
关于 serverTimezone 的官方说明
Override detection/mapping of time zone. Used when time zone from server doesn’t map to Java time zone
修改一下 jdbc url,通过serverTimezone
指定时区为 GMT+8
:jdbc:mysql://localhost:3306/test?serverTimezone=GMT%2B8&useSSL=false
再次执行代码:
2020-05-14T08:00