For security reasons, Javascript can not access a client's hard drive.
HTML provides an input control of type "file" which allows the user to select a file and post it to the server as part of a multi-part encoded form. By design, there is very little you can do to interact with this control from your Javascript code.
On the server, you can use one of several third party products to parse this multipart form and work with the uploaded file.
See:
http://faq.javaranch.com/java/FileUpload For more information on file uploads.