springboot + mybatis多數據庫 + druid連接池配置成功。正常運行后，訪問第一個數據庫后訪問第二個數據庫，再去訪問第一個數據庫 會報錯:
### Error querying database. Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 8,451 milliseconds ago. The last packet sent successfully to the server was 0 milliseconds ago.
### The error may exist in com/bwton/dist/dao/sys/DictDao.xml
### The error may involve defaultParameterMap
### The error occurred while setting parameters
### SQL: select id,code,value,caption,status, create_user,create_time,update_user,update_time from dictionary where code = ? and value <> "!" and status = "1" order by value
### Cause: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 8,451 milliseconds ago. The last packet sent successfully to the server was 0 milliseconds ago.
; SQL []; Communications link failure
The last packet successfully received from the server was 8,451 milliseconds ago. The last packet sent successfully to the server was 0 milliseconds ago.; nested exception is com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 8,451 milliseconds ago. The last packet sent successfully to the server was 0 milliseconds ago.
at org.springframework.jdbc.support.SQLExceptionSubclassTranslator.doTranslate(SQLExceptionSubclassTranslator.java:98)
網上查了下，原因是
MySQL服務器默認的“wait_timeout”是28800秒即8小時(查看mysql實際wait_timeout可以用sql命令:show global variables like ‘wait_timeout’?，意味着如果一個連接的空閑時間超過8個小時，MySQL將自動斷開該連接，而連接池卻認為該連接還是有效的(因為並未校驗連接的有效性)，當應用申請使用該連接時，就會導致上面的報錯。
解決方法：
- 1、修改my.cnf：
[mysqld]
wait_timeout=31536000
interactive_timeout=31536000
將過期時間修改為1年。 - 2、在連接URL上添加參數：&autoReconnect=true&failOverReadOnly=false
我的解決采用的是第二種方法，在URL后面加上&autoReconnect=true&failOverReadOnly=false
網上搜索參考自：
https://blog.csdn.net/a704397849/article/details/93797529
在此也感謝開發老表的協助。