老师好，在验证AreaController.java的时候没有返回json，报错了
报错信息：
{“success”:false,“errMsg”:“org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.exceptions.PersistenceException: \r\n### 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!\r\n### The error may exist in file [F:\com\o2o\out\artifacts\o2o_war_exploded\WEB-INF\classes\mapper\AreaDao.xml]\r\n### The error may involve com.chr.o2o.dao.AreaDao.queryArea\r\n### The error occurred while executing a query\r\n### 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!”}