问题：
org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.exceptions.PersistenceException: ### Error querying database. Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database! ### The error may exist in com/ssmbuild/dao/BookMapper.xml ### The error may involve com.ssmbuild.dao.BookMapper.queryAllBook ### The error occurred while executing a query ### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Failed to obtain JDBC Connection; nested exception is java.sql.SQLException: Connections could not be acquired from the underlying database!
解决：
尝试了很多方法，最后还是url的问题：
原有的：
jdbc.driver=com.mysql.cj.jdbc.Driver jdbc.url=jdbc:mysql://localhost:3306/ssmbuilduseSSL=false&useUnicode=true&characterEncoding=utf-8&serverTimezone=CST jdbc.username=root jdbc.password=***
现在的：
jdbc.url=jdbc:mysql://localhost:3306/ssmbuild?characterEncoding=utf-8&serverTimezone=GMT
就可以连接成功啦
