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From "Carsten Ziegeler" <cziege...@sundn.de>
Subject RE: [RT] Environment Revamping
Date Fri, 19 Oct 2001 08:44:15 GMT
> Berin Loritsch wrote:
>
> Currently, the Environment system has grown to provide an abstraction
> layer so that Cocoon logic can function equally well depending on whatever
> the environment is.  This is a good thing, and in my opinion very
> necessary.
> However, what we have in our API can get confusing both for Cocoon app
> developers, and for environment adaptor providers.
>
> Because Cocoon began life as a Servlet, the environment is heavily slanted
> in that direction.  While I do not want to reinvent the wheel that the
> servlet vendors have created, we can simplify our API so that app
> developers
> have an easier time.  Currently, the Environment consists of the following
> interfaces:
>
> * Environment
> * Context
> * Cookie
> * Redirector
> * Request
> * Response
> * Session
> * Source
> * SourceResolver
>
> In addition to this we have the Avalon Context that we are using within
> the rest of the API for Cocoon system properties.  Some of this is a bit
> much, and can be merged, and we can have a simpler API because of it.
> Granted that this would require deprecating some pieces in the HEAD
> branch of CVS, but I think we would be better for it in the long run.
> First, we have to consider what each piece is used for.
>
> INSTALLATION SPECIFIC API
> org.apache.avalon.framework.context.Context
> org.apache.cocoon.environment.Context
> SourceResolver
> Source
>
> SESSION SPECIFIC API
> Session
>
> REQUEST SPECIFIC API
> Redirector
> Request
> Response
> Map (ObjectModel)
>
> PERSISTENT CLIENT STORAGE
> Cookie
>
>
> In addition to all this, the ObjectModel is simply a Map that
> allows access
> to all of the APIs as we need them.  It is clear that too many
> indirections
> (i.e. Maps) create a more cluttered API.  What should we do then?  Clearly
> there are two major categories of Context.  There is the system
> context which
> provides meta information about the installation.  Then there is
> the request
> specific context which allows us to pass information between stages, and
> access the session and client storage mechanisms.
>
> In order to simplify, I believe that there should be 2 Context objects to
> worry about: SystemContext and RequestContext.  The SystemContext object
> would extend the AvalonContext--and be passed to any Contextualizable
> Component.  So what would this look like:
>
> public interface SystemContext extends
> org.apache.avalon.framework.context.Context {
>     Source resolve(String uri);
>     org.apache.cocoon.environment.Context getEnvironmentContext();
>     Object get(Object key); // from Avalon context
> }
>
> This removes the need for the SourceResolver interface to be
> exposed or passed
> as an argument to Components.  Components that do not need it or
> use it will
> have access to a simpler API.
>
The intention of this interface is very good, I like it, but
I see one (more technical) problem here: the resolve() method
is Environment or Request dependant. This means, if a component
(e.g. the store) is contextualized at startup and gets the
SystemContext, the resolving of resources must be done
with the current environment in mind which might result in
different resources.
This resolving with respect to the current environment is
of course necessary for all sitemap components (generators
etc).
If we get this working: +1

What do you mean with the org.apache.cocoon.environment.Context
object? Is this the RequestContext mentioned below?


> The other Context woudl be the RequestContext.  That API would be
> like this:
>
> public interface RequestContext extends Map {
>     Request getRequest();
>     Session getSession();
>     Session getSession(boolean forceNew);
>     Response getResponse();
>     void redirect(String uri); // throws IllegalStateException if
> called after generator setup.
>     Object get(Object key); // from Map
>     void put(Object key, Object value); // from Map
> }
>
> This makes the RequestContext compatible with ObjectModel as it
> stands now--
> not forcing any MAJOR changes to the API.  It also removes the
> need of exposing
> the Redirector interface to the clients as a passed argument.
> While it may
> seem tempting to do so, most developers will get the clue very
> quickly that
> it can only be done from the SetUp method.  This will expose it
> to be used to
> generators and transformers alike, but the distinct difference is that the
> setup and generate commands are separate.
>
> This also simplifies client code--and the get/put methods in the
> RequestContext,
> but it also minimizes the overhead involved in looking up the
> specific environment
> interfaces from a generic Map.
>
> You'll notice that the Environment interface is missing.  That is
> because the
> Environment interface has been identified as the contract between
> the sitemap
> and the environment that Cocoon is living in.
>
> Lastly, this will also open up API optimizations in that we can
> simplify the
> signatures to setUp(RequestContext context, String source,
> Parameters params);
> If there is some new interface that needs to be supplied to the sitemap
> components, it will be done through the RequestContext or
> SystemContext objects
> as is appropriate.
>
+1

What about the Interface Cookie you mentioned above? I personally would
like to clean up Request/Response interfaces.
There are certainly Environments which do not use Cookies and for
example don't know anything about headers. So I would like to separate
them from the Request/Response so that one could test if the
current environment supports this feature or not.

By the way: About what timeframe and version are we talking here?

Carsten
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