Apache HttpComponents HttpClient - MIME coded entities
mime-util is a simple to use, small, light weight and fast open source java utility library that can detect MIME types from files, input streams, URL's and byte arrays. Due to the use of regular expressions and the java.nio packages it requires at least Java 1.4.
Apache James :: Mime4j :: Assembly
Apache James :: Mime4j :: Core
Support for configurable MIME type mapping and querying
Support for multipart MIME POSTs
Java MIME Document Object Model