Class mypackage.TripsServletTable is not a Servlet

Question

I've seen several postings similar to this, but still haven't been able to solve my problem. Maybe another set of eyes would help.
I have an html file in webapps/Trips, with the line:
<form action = "http://localhost:8080/Trips/servlet/TripsServletTable" method = "post">
I've also tried:
<form action = "/servlet/tripsTable" method = "post">
and
<form action = "/Trips/tripsTable" method = "post">
my web.xml file contains
<servlet>
     <servlet-name>tripsTable</servlet-name>
     <servlet-class>mypackage.TripsServletTable</servlet-class>
</servlet>
<servlet-mapping>
     <servlet-name>tripsTable</servlet-name>
     <url-pattern>servlet/tripsTable</url-pattern>
</servlet-mapping>
My class file is in the classes/mypackage directory under WEB-INF and is name TripsServletTable.
I either get the message :
Class mypackage.TripsServletTable is not a Servlet
or that the servlet is not available (depending on which of the above options is in place). FYI, This directory was running with tomcat 3.2.3. Any suggestions would be appreciated.

Answer 1

Thanks for the quick reply. Yes, my class does extend HttpServlet. Also, I had previously tried (and have since tried again) having the url pattern start with a / character. With these changes the error message is now:
The requested resource (/Trips/servlet/TripsServletTable) is not available.
By the way, I am running Tomcat 5.5.9. Any other suggestions would be appreciated. I admit I am pretty confused about what to put in the <form action = "..."> portion of my html file, as I've seen different recommendations from various sources.