java.net.UnknownHostException: hostname

用jsp连接mysql数据库时出现了这样的错误，怎么解决？

com.mysql.jdbc.CommunicationsException: Communications link failure due to underlying exception:

** BEGIN NESTED EXCEPTION **

java.net.UnknownHostException
MESSAGE: hostname

STACKTRACE:

java.net.UnknownHostException: hostname

提示得很清楚，没有找到hostname,你怎么写的连接字符串

hostname不能识别。 应该是mysql数据库的ip有问题吧