Re: [Knobot-devel] a question on the ordering of TypeHandler

[<re...@gm...>]

hi david,

- FileServerFilter is a rwcf:TypeHandler
- IEFixFilter is a rwcf:Filter
- rwcf:TypeHandlerS get executed by the TypeChainFilter which is an
rwcf:Filter.

What happens is the following:
1. the rwcf:FilterS gets ordered by priority, higher priority are
excecuted first, lower if and only if the higher-priority filters
forward the request
2. With prirority 500 the TypeHandlerFilter comes into action, this
creates a chain of TypeHandler so that what's returned by one
TypeHandler is the input-type for the next, the goal is to create a
chain which return a content-type acceptable by the client agent.

From: http://development.osar.ch/documentation (this should be moved to
a wymiwyg-site...)

The Type Handler Filter is a filter which creates a list of
TypeHandlers  and forwards the request to this list. TypeHanlers are
itself very similar to Filters, in fact they implement the same java clas=
s.

    * The description of a TypeHandler contains the media type it
returns, if the handler requires some input data the media-types such
data must be is specified. (an exception for TypeBlindHandlers as well
as for TypeHandlers implementing the Java Interface TypeHandler, this
rarely used features need some redesign)
    * The desciption of a TypeHandler may force authentification by
being of type rwcf:PermissionEnforcer


The Type Hanlder Filter constructs the chain of TypeHandlers  by
iterating through the available TypeHandlers  in descending order of
rwcf:priority, when a TypeHandlers matches the current request and  has
the desired target-typeit if added to the chainand the iteration through
the available TypeHandlers starts over omiting  those already in the
chain. This processed is repeated till a terminal chain is found, a
terminal chain is one that ends with a TypeHandler which needs no input
data.
basing on the request it receives so that the changes made by previous
Filters inluence the selection of TypeHandlers.

3. If no type-handler chain can be created the request is forwarded to
the next rwcf:Filter after TypeHandlerFilter, possibly getting at a
filter generating a 404 or a method-not-supported error page.


So setting a low priority to IEFixFilter will cause the filter to be
executed iff no previous filter can handle the request, which includes
that no type-handler filter chain can be created, which in turn includes
that FileServerFilter cannot serve a file.

reto

PS: http://jena.hpl.hp.com/juc2006/proceedings/bachmann-gmur/paper.pdf
also has some infos about FilterS and TypeHandlerS

dbu wrote:
> hi,
>
> i am experimenting with caching and the IEFixFilter.
> i realised that the FileServerFilter gets called after the IEFixFilter.=
=20
> the iefix-section.rdf defines the priority of the iefix, fs-section.rdf=
=20
> that of the fileserver.
> i tried to put iefixfilter priority lower than that of the filefilter, =

> but this results in iefixfilter not being used at all.
> how can i control which filters are used on a request and in what order=
?=20
> or can't i use several handlers on one request?
>
> cheers,david
>
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