ServletRequest.getInputStream returns empty content and i learned why.

I make a post to a web application. the problem is on the URL,
I wrote "http://localhost/appname" and without a request path.
so tomcat(not know if others do the same) will make a empty GET method on
welome page. So when i debug, it runs into the right servlet but with GET method
and empty body.
That why it seems that ServletRequest.getInputStream cannot read anything out.