为提高效率，提问时请提供以下信息，问题描述清晰可优先响应。
- 【TiDB 版本】：v4.0.4
- 【问题描述】：javaWeb程序在切换tidb数据库后，偶尔会抛出db连接断开异常，频率是每天4次左右。
框架：springboot2.2.2.RELEASE
连接池：druid1.1.20
#连接池配置：
#####datasource druid pool
spring.datasource.dynamic.druid.filters= stat
spring.datasource.dynamic.druid.initial-size=5
spring.datasource.dynamic.druid.max-active=300
spring.datasource.dynamic.druid.min-idle=16
spring.datasource.dynamic.druid.max-wait=60000
spring.datasource.dynamic.druid.time-between-eviction-runs-millis=360000
spring.datasource.dynamic.druid.min-evictable-idle-time-millis=360000
spring.datasource.dynamic.druid.validation-query=SELECT 1 FROM DUAL
spring.datasource.dynamic.druid.test-while-idle=true
tidb查询数据源
spring.datasource.dynamic.datasource.datastidb.username=USERNAME
spring.datasource.dynamic.datasource.datastidb.password=PASSWORD
spring.datasource.dynamic.datasource.datastidb.url=jdbc:mysql://TIDB_DB?useUnicode=true&useSSL=false&allowMultiQueries=true&zeroDateTimeBehavior=convertToNull&serverTimezone=Asia/Shanghai&zeroDateTimeBehavior=convertToNull&autoReconnect=true&failOverReadOnly=false
spring.datasource.dynamic.datasource.datastidb.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.dynamic.datasource.datastidb.type=com.alibaba.druid.pool.DruidDataSource
#注：为了不暴露真实的数据源，USERNAME，PASSWORD和TIDB_DB是使用临时的字符串
异常信息：
com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure
The last packet successfully received from the server was 29,742 milliseconds ago. The last packet sent successfully to the server was 29,742 milliseconds ago.
at com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:174)
at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64)
at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:953)
at com.mysql.cj.jdbc.ClientPreparedStatement.execute(ClientPreparedStatement.java:370)
at com.alibaba.druid.filter.FilterChainImpl.preparedStatement_execute(FilterChainImpl.java:3461)
略。。。
