Class is not a servlet

[Luca Sabbio]

Hi, I'm working with Java 1.5.0.06, Tomcat 5.5.16 with Xindice 1.1b4 and Cocoon 
2.1.10 deployed (and working).

I try to run a simple web application based on a servlet that update the 
Xindice XML DB
By the command line the PartsXupdate.java is compiled and the 
PartsXupdate.class works.

import org.xmldb.api.base.*;
import org.xmldb.api.modules.*;
import org.xmldb.api.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;


public class PartsXupdate {
   public static void main(String[] args) throws Exception {
      Collection col = null;
      try {
         String driver = "org.apache.xindice.client.xmldb.DatabaseImpl";
         Class c = Class.forName(driver);
         
         Database database = (Database) c.newInstance();
         DatabaseManager.registerDatabase(database);
         
         col = 
DatabaseManager.getCollection("xmldb:xindice://localhost:8080/db/test");
         
String xupd = "<xupdate:modifications version=\"1.0\" 
xmlns:xupdate=\"http://www.xmldb.org/xupdate\";>"  + 
"<xupdate:insert-after select=\"/scheda/info\">"  +
"<xupdate:element name=\"commento\">Bel libro!</xupdate:element>"  + 
"</xupdate:insert-after>"  + 
"</xupdate:modifications>"; 



    String nome = "4.xml";   

            /* We are using XUpdateQueryService */
            XUpdateQueryService service =
               (XUpdateQueryService) col.getService("XUpdateQueryService", 
"1.0");
               
            service.updateResource(nome, xupd);
      }
      catch (XMLDBException e) {
         System.err.println("XML:DB Exception occurred " + e.errorCode);
      }
      finally {
          if (col != null) { col.close();}
      }
   }
}

But when I deploy the application on Tomcat 
and I do my post action http://localhost:8080/PartsXupdate/PartsXupdate from 
the form of provajava.html 
I get this error:
javax.servlet.ServletException: Class PartsXupdate is not a Servlet

I think that my web.xml is ok

<?xml version="1.0" encoding="ISO-8859-1"?>

<web-app xmlns="http://java.sun.com/xml/ns/j2ee";
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd";
    version="2.4">

  <display-name>esempio_servlet_xupdate</display-name>
  <description>
     Esempio di uso di servlet_xupdate
  </description>

<!-- JSPC servlet mappings start -->

<servlet>
        <servlet-name>PartsXupdate</servlet-name>
        <servlet-class>PartsXupdate</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>PartsXupdate</servlet-name>
        <url-pattern>/PartsXupdate</url-pattern>
    </servlet-mapping>

<welcome-file-list>
  <welcome-file>provajava.html</welcome-file>
</welcome-file-list>

</web-app>

Also classpath would be ok. Is there something to set in Tomcat?
I've read many mailing list and tried some changes but without results,
any suggestion would be appreciate.
Thanks