Connections could not be acquired from the underlying database!

Connections could not be acquired from the underlying database!

 

以上问题可能有一下缘由形成：

1，驱动配置有误：driver=com.mysql.jdbc.Driver
2，数据库链接地址有误：url=jdbc:mysql://localhost:3306/test?3useUnicode=true&characterEncoding=utf8
3，密码或账号有误：username=root
      password=root

4，数据库未启动或无权访问

5，项目未引入对应的驱动jar包mysql-connector-java-5.1.6-bin.jar

6,mysql root没有远程访问的权限，须要增长权限，增长权限的步骤以下：
进入mysql数据库：
grant all privileges on *.* to 'root'@'%' identified by 'root' with grant option;
flush privileges;