code: public FilterHolder addFilterPathMapping(String pathSpec, String filterName, int dispatches)
      {
          FilterHolder holder = (FilterHolder)_filterMap.get(filterName);
          if (holder==null)
              throw new IllegalArgumentException("unknown filter: "+filterName);
          
          FilterMapping mapping = new FilterMapping(pathSpec,holder,dispatches);
          _pathFilters.add(mapping);
          return holder;
      }
docs: Add a mapping from a pathSpec to a Filter.
  @param pathSpec The path specification
  @param filterName The name of the filter (must already be added or defined)
  @param dispatches An integer formed by the logical OR of FilterHolder.__REQUEST,
  FilterHolder.__FORWARD,FilterHolder.__INCLUDE and/or FilterHolder.__ERROR.
  @return The holder of the filter instance.