web-app not working after upgrade 7.4 to 8.1

Hello experts,

I have recently upgraded my database from 7.4 to 8.1 and migrated all data.

In order to be able to use my web-app, I replaced the old jdbc.jar with
postgresql-8.1-407.jdbc3.jar in WEB-INF/lib/.

Restarted Tomcat (4.1.31) - and later even redeployed the webapp.

I keep getting no database connection - as if the postmaster were not
started.

Apparently I have ignored something basic - but no idea what to look at.
This is actually my first fully working webapp using Struts and Tomcat
on Linux - so maybe my problem is really a Tomcat issue.

I have attached part of my coding of the Struts-Action, the exception
occurs with the message "Presumably database is down."

Any hint is apreciated.

-----------------------------------


public ActionForward execute( ActionMapping mapping,
                                   ActionForm form,
                                   HttpServletRequest request,
                                   HttpServletResponse response )
                 throws Exception
{
    HttpSession sitzg = request.getSession();
    ConnectionPool pool = (ConnectionPool) sitzg.getAttribute( JDBC );
    if (pool == null)
    {
       try
       {
          pool = new ConnectionPool( driver, dburl, username, password,
initConn );
          sitzg.setAttribute( JDBC, pool );
       }
       catch ( SQLException e )
       {
          System.out.println( e.getMessage() );
          System.out.println( "Cannot connect to database " + database );
          e.printStackTrace();
       }
       catch ( ClassNotFoundException e )
       {
          System.out.println( e.getMessage() );
          System.out.println( "Falscher Treibername in den Properties: "
+ driver );
          e.printStackTrace();
       }
       if (pool == null)
       {
          throw new SQLException( "ERROR: NULL pool created!  Presumably
database is down." );
       }

-----------------------------------

Regards,

Wolfgang Rinnert
wrinnert@web.de