Did you ever get this figured out. With Leonard's
prodding, I finally got mine to work. The hitch
was that the class  was in a package of the same name
(a standard practice) and both the class name in
web.xml and the path to the class must be fully
qualified. In your case (if this is your problem)
you would use:

<servlet>
<servlet-name>a1</servlet-name>
<servlet-class>a1.a1</servlet-class>
</servlet>

and your class should be at <appBase>/classes/test/a1/a1.class

When you have everything like this, restart Tomcat
and try again. As Leonard said, with your servlet
mappin you should invoke it with:

http://localhost:8080/test/a1

If this doesn't help, we can keep plugging. I'm still
a little concerned about how that "test" subdirectory
plays out. I didn't have that complication. As you
can see, I'm no Java guru myself.