Servlet error: Error instantiating servlet

Question

I have a relatively simple project that uploads a zip file to a servlet, however, when POST to the servlet I suddenly started getting the following error:
500 Internal Server Error
Servlet error: Error instantiating servlet 'ConfirmSiteReport'. Servlet class uploader.ConfirmSiteReport not found in web-application SiteReport-Uploader-webapp
I've checked the web.xml and have not found anything wrong, and I dont recall changing anything in the project config when this error started, and the class file is in the classes directory.:
<servlet>
<servlet-name>ConfirmSiteReport</servlet-name>
<servlet-class>uploader.ConfirmSiteReport</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ConfirmSiteReport</servlet-name>
<url-pattern>/confirmsitereport</url-pattern>
</servlet-mapping>

Answer 1

Using version 10.1.3.1. I commented everything out and printed out a simple hello world and the servlet worked, when I uncommented everything it throws a 500 error with no log entries, warnings, or anything. I'm thinking something I'm importing is conflicting with the OC4J servlet container.
package uploader;
import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringReader;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Vector;
import java.util.zip.ZipEntry;
import java.util.zip.ZipException;
import java.util.zip.ZipFile;
import java.util.zip.ZipInputStream;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;