mysql 错误：The driver has not received any packets from the server.

com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:400)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1038)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:339)
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2247)
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2280)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2079)

........

出现以上错误，先尝试使用mysql客户端连接下需要连接的mysql server 数据库。

此错误为，jdbc启动，尝试连接相应地址的数据库(会发送一些用于测试的sql语句)，结果没有响应，即连接失败。