On 07/05/20 10:37, Emond Papegaaij wrote:
Hi Martin,

I know what these id's are for, and this still works as expected.
However, your claim about stable id's on stateless pages currently
does not work as you describe. The id's of behaviors is stored in the
component they are added to, also when the component is stateless. As
you said, a stateless page is discarded at the end of a request,
including the components and the recording of the stable id's. On the
next request, the page is reconstructed, but Wicket cannot guarantee
that the behavior id's are the same. For example, when you
conditionally add a behavior, it influences the id's of the behaviors
added after it. I want the documentation to reflect this, and use this
to optimize the code. IMHO there's no point in storing id's for
stateless behaviors for the next request. If you absolutely need this
guarantee, you should make your behavior stateful.

One difference between my implementation and the current one is that
behaviors with stable id's are currently moved to the front.

Hi Emond,

I don't perfectly understand what you mean with 'moved to the front'. Could please explain it? To be clear about stateless behavior and ids, actually we can have a "predictable" id for them if we avoid things like conditional adding, etc... In short we can have stable ids for stateless behaviors but the responsibility for them is up to the developer and not to the framework. This is critical to make complex stateless components (for example AJAX links) properly work. I guess your PR preserve this condition. And yes, I agree there's no need for storing stateless behaviors ids.

makes the id's a bit more stable. I'm planning to do something
similar, via a new method on Behavior. This should all be API
compatible. I hope this clarifies my intent.


On Thu, May 7, 2020 at 9:23 AM Martin Grigorov <mgrigo...@apache.org> wrote:
Hi Emond,

The behavior id is something internal to Wicket.
It is used *by* Wicket to find the requested behavior in a Component.
For example if a Component has more than one Ajax behaviors (yes, Ajax
behaviors could be stateless too since 7.4.0. Before that there was a
project in WicketStuff) it uses the id (extracted from the special
parameter in the url) to find which behavior exactly should be invoked.
In case of stateful page the ids are stored with page and later
In case of stateless page (with stateless Ajax behaviors) the whole page is
discarded at the end of request 1 but at request 2 a new page is created
from scratch with all its components and their behaviors. Here the id
*must* be the same as in request 1, otherwise Wicket may execute another
behavior's onRequest(). So, the ids must be stable in case of stateless as

On Wed, May 6, 2020 at 9:28 PM Emond Papegaaij <emond.papega...@gmail.com>


While running, I came up with a solution for which only a minor change
to the contract of the method is needed: ids for stateless behaviors
will be stable within a single requests, but can change over requests.
I think this is reasonable, given the way stateless components work.

I would like to change the documentation to read:
Gets a stable id for the specified behavior. The id remains stable
from the point this method is first called for the behavior until the
behavior has been removed from the component. For {@linkplain
Behavior#getStatelessHint(Component) stateful} behaviors, this stable
id is retained over requests. For stateless behaviors, the id can
change between requests.


On Wed, May 6, 2020 at 5:54 PM Emond Papegaaij
<emond.papega...@gmail.com> wrote:
Hi Andrea,

Stateful is fine, stateless is not. A component cannot keep a stable
id when it's stateless. I'm trying out a change that forbids
getBehaviorId() for stateless behaviors, and I'm hitting a few tests
with stateless ajax. I don't see how this is supposed to work anyway.
We request the component to store the id of a certain behavior, but it
must do so in a stateless way. IMHO that's impossible. The component
will be discarded, along with its state and the stored id at the end
of the request. No way of guaranteeing that the same component with
the same behavior at the same index will exist at the next request.

This brings me back to my suggested change in the documentation: only
stateful behaviors have guaranteed stable ids. You can request the id
of a stateless behavior, but (in my current implementation) it may
change when you remove behaviors from the component.


On Wed, May 6, 2020 at 5:41 PM Andrea Del Bene <an.delb...@gmail.com>

On 06/05/20 16:52, Emond Papegaaij wrote:
Hi all,

During my refactoring of the component state (WICKET-6774) I noticed
that behavior ids are currently stored in a very inefficient way: an
ArrayList is added to Component data to store references to behaviors
with a stable id. On my branch I have eliminated this ArrayList,
greatly reducing the size of components with stateful behaviors (such
as AjaxLink).

A behavior gets a stable id when it is stateful to be able to render
this id in an URL. However, at the moment, it also gets a stable id
when Component.getBehaviorId is called for that particular behavior.
This is also documented in the method's javadoc. Do we really need
this last part? It complicates the code a lot. In our code base nor
Wicket can I find a single place where this is actually used.
Actually I see that Component.getBehaviorId is used in
AbstractAjaxTimerBehavior.getTimerId() and
AbstractDefaultAjaxBehavior.onBind() which are however stateful
I would like to suggest a change in the javadoc to state that stable
ids are only guaranteed for stateful behaviors and change this in
Wicket 9. The actual change in the implementation is not yet finished
and does not need to ship in 9.0.0, but feel I cannot change the
contract of a method in a minor release.

Best regards,

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