This might be an old topic, but it would be handy to write down the common solutions for the file upload. Just for your reference:

• Jason Hunter's MultipartRequest (available from http://www.servlets.com)
  
• Apache Jakarta Commons Upload (package org.apache.commons.upload) "makes it easy to add robust, high-performance, file upload capability to your servlets and web applications"
  
• CParseRFC1867 (available from http://www.servletcentral.com).
  
• HttpMultiPartParser by Anil Hemrajani, at the isavvix Code Exchange
• There is a multipart/form parser availailable from Anders Kristensen (http://www-uk.hpl.hp.com/people/ak/java/, ak@hplb.hpl.hp.com) at http://www-uk.hpl.hp.com/people/ak/java/#utils.
  
• JavaMail also has MIME-parsing routines (see the Purple Servlet References).
  
• Jun Inamori has written a class called org.apache.tomcat.request.ParseMime which is available in the Tomcat CVS tree.
  
• JSPSmart has a free set of JSP for doing file upload and download.
  
• UploadBean by JavaZoom claims to handle most of the hassle of uploading for you, including writing to disk or memory.
  
• There's an Upload Tag in dotJ

Once you process the form-data stream into the uploaded file, you can then either write it to disk, write it to a database, or process it as an InputStream, depending on your needs. See How can I access or create a file or folder in the current directory from inside a servlet? and other questions in the Servlets:Files Topic for information on writing files from a Servlet.

Personally, I'd highly recommend COS package for file upload purpose. Reference as below:

http://www.thebook-demo.com/java-server/servlets/upload.html

http://www.servlets.com/cos/javadoc/com/oreilly/servlet/MultipartRequest.html

http://www.servlets.com/cos/ (download the cos package from here)