file_upload.java

import javax.servlet.http.*;
import javax.servlet.ServletOutputStream;
import java.io.InputStream;

import org.apache.commons.fileupload.FileItemIterator;
import org.apache.commons.fileupload.FileItemStream;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

public class ExampleServlet extends HttpServlet {
        ServletFileUpload upload; 
	public void init() {
		this.upload = new ServletFileUpload();
	}
        doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		FileItemIterator iter = null;
		FileItemStream item = null;
		try {
			iter = upload.getItemIterator(req);
		} catch (FileUploadException fue) {
			fue.printStackTrace();
		}
		try {
			item = iter.next();
		} catch (FileUploadException fue) {
			fue.printStackTrace();
		}
		InputStream in = item.openStream();
        }
}

Example of using Apache Commons FileUpload
http://commons.apache.org/fileupload/using.html