如何在Android应用程序上基于服务器消息执行不同的任务？

I created working chat application in android and java based server using TCP/Ip . But now i want to perform tasks like vibration in phone when server send particular string such as "Vibrate" ... I tried if servermsg="Vibrate" (And called another class) but not working... Help Pls....I created working chat application in android a