code: public void addServletHolder(ServletHolder holder)
      {
          ServletHolder existing = (ServletHolder)
          _nameMap.get(holder.getName());
          if (existing==null)
              _nameMap.put(holder.getName(),holder);
          else if (existing!=holder)
              throw new IllegalArgumentException("Holder already exists for name: "+holder.getName());
          addComponent(holder);
      }
docs: Register an existing ServletHolder with this handler.
  @param holder the ServletHolder to register.