Q:

Android tethering web server

I am looking for a method to display a webpage when somebody connects to my hotspot
.Is there a way I could implement this? 

A:

Not sure what the Android access restrictions are, but assuming your app has the network read / write / bind permissions, the simplest thing to do is simple embed Jetty and get it to start a server on the specified port, example are : http://wiki.eclipse.org/Jetty/Tutorial/Embedding_Jetty
EDIT: Upon further reading of your question that's just the start, you will need to block all other network traffic until the client has accepted the captive portal above. 
Hope I helped
md_5

