I'm not sure why but this question gets asked a lot. Search this forum with keyword "destroy" and you will find plenty of discussions on the subject.
This question indicates a gap in your understanding of the servlet life-cycle and the methods involved. There is a link to the servlet spec in my signature. The first few chapters cover this. In particular, look at SRV.2.3
Purpose of destroy() method is to know when servlet is going out of service OR In other words, before container decides to take out servlet from service, it will call this method, so that you can do your clean up process.
servlet life-cycle is init() --> service(..) --> destroy() which is maintained by servlet Container and it doesn't make any sense to call these methods explicitly.
destroy is a call back method and container is suppose to call that not you .But as you have asked whether this can be invoked , yes you can.But that would be just as any other method call.The purpose of destroy method is not that.