The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.

启动类上加：

@MapperScan(value = {"com.example.demo.mapper"})

This issue has appeared in the testing of mybatis batch insert using xml file,
And I check the different with the correct configuration in the old project.
The problem is the mapperScan annotation is missing.
Then I add the mapperScan to the startup class.
The issue closed.