NanoHTTPD - http://elonen.iki.fi/code/nanohttpd/

This guy wrote a pure Java webserver as just one script. Intended for hackers to embed.

Tiny Java Web Server - http://tjws.sourceforge.net/

It doesn't look minimalist enough.

A bare minimum web server for android platform - http://www.androiddevblog.net/android/a-bare-minimum-web-server-for-android-platform

This uses the Android HTTP libraries: org.apache.http.