For the second question...
You want to use the load-on-startup element in the web.xml file.  The 
description from the servlet spec is provided below.  This tag belongs 
inside the servlet tag for the servlet that should be loaded.

<servlet>
    <servlet-name>foo</servlet-name>
    <load-on-startup></load-on-startup>
</servlet>

The load-on-startup element indicates that this servlet should be
loaded on the startup of the web application. The optional contents of
these element must be a positive integer indicating the order in which
the servlet should be loaded. Lower integers are loaded before higher
integers. If no value is specified, or if the value specified is not a
positive integer, the container is free to load it at any time in the
startup sequence.

> 2      the other question is :i want to one of my servlet must be loaded 
> into the
>        memory,AS SOON AS my tomcat is started,how can i do,modify which 
> configuration 
> 	files?and how? or maybe it is default!
> 
> thanks alot.