Is it a bug in MySQL or in java-connector？

最新推荐文章于 2025-10-30 16:56:01 发布

最新推荐文章于 2025-10-30 16:56:01 发布 · 156 阅读

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当使用MySQL 5.1.27版本时，通过Java连接器尝试设置服务器字符集为utf8mb4遇到了数据插入错误。该问题发生在先将服务器默认字符集设置为GBK的情况下，再试图通过Java连接器动态更改字符集。分析显示，Java连接器根据服务器的默认字符集处理数据，而服务器并未更新其默认字符集信息。

Description

In mysql-connector-java-5.1.27, the charset utf8mb4 is supported. But the steps and result bellow looks buggy.

1、 set character_set_server=gbk in my.cnf

2、 start mysql

3、 execute set global character_set_server=utfmb4;

4、 insert a data with utf8mb4 characters

Result: error data inserted.

Analysis

Direct reason: Java connector believes that the server use gbk as the default set, so deal the data with the rule of gbk;

Deeper reason:

1\ set global character_set_server=utfmb4 just change the global_system_variables, but not the default_charset_info and default_character_set_name.

2\ when handshake, MySQL server writes server characteristics to client, using default_charset_info->number, 28, which is the CharsetIndex of gbk.

Compare

As comparison, the steps change to

1、 set character_set_server= utfmb4 in my.cnf

2、 insert a data with utf8mb4 characters

Result: correct data inserted.

Because the default charset is utfmb4 now, the connector treats dada correctly.

Discussion

There are two ways to resolve this problem.

1\ MySQL sends the current character info number in global_system_variables when handshake

2\ Java connector get the correct character to use by “select @@character_set_server;”

So , is it a bug for MySQL or java-connector?