Java线上报错，mysql数据库

Question

线上报错：
{timestamp: "2023-01-17 14:29:14", status: 500, error: "Internal Server Error",…}
error: "Internal Server Error"
message: "status 500 reading ApiPlatformService#createQr(QRCodeVO); content:↵{"timestamp":"20230117 14:29:14844","status":500,"error":"Internal Server Error","message":"nested exception is org.apache.ibatis.exceptions.PersistenceException: \n### Error querying database. Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure\n\nThe last packet successfully received from the server was 2 milliseconds ago. The last packet sent successfully to the server was 2 milliseconds ago.\n### The error may exist in URL [jar:file:/app.jar!/BOOT-INF/classes!/mapper/dict/SysDictMapper.xml]\n### The error may involve com.hyzk.platform.api.controller.dict.dao.SysDictMapper.get\n### The error occurred while executing a query\n### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure\n\nThe last packet successfully received from the server was 2 milliseconds ago. The last packet sent successfully to the server was 2 milliseconds ago.","path":"/file/createQcEqument"}"
path: "/incoming/confirm-receipt"
status: 500
timestamp: "2023-01-17 14:29:14"
摸不着头脑 不知道是因为啥

Answer 1

Failed to obtain JDBC Connection
数据库没有连上，检查字符串是否正确，用工具测试数据库到底能不能连上，开没开，防火墙拦没拦