[jsr-314-open] [NEW] <f:ajax> and <f:validateBean> - consistent wrapping solution needed?

Gang - In JSF 2.0 we are introducing two core tags that wrap/enhance component subtrees: f:ajax and f:validateBean. f:ajax is used to enable Ajax behavior for a subtree, eg: f:validateBean is used to enable bean validation for a subtree, eg: Of course, both tags can also be used in their nested form to enable Ajax/bean validation on a single component. We currently use different implementation strategies for the "wrapping" behavior. f:ajax uses a handler execution-time solution. AjaxHandler maintains a stack that keeps track of the current nested state of <f:ajax> tags. Before apply child handlers, AjaxHandler pushes the current Ajax-related info onto this stack. When child/descendent handlers are applied, ComponentTagHandlerDelegateImpl checks this stack to get at the current Ajax-related state and performs the necessary work to wire up an AjaxBehavior to the component. Finally, after child handlers have been processed, AjaxHandler pops the stack, and we're done. The end result of the f:ajax solution is that once handlers have finished executing, we have a fully configured component tree. No further processing is necessary to apply "inherited" Ajax behavior. f:validateBean uses a solution which is split between tag/handler execution-time, validation-time and render-time. BeanValidatorHandler/ValidatorTagHandlerDelegateImpl set up well known properties on the parent component's attribute map (eg. BeanValidator.VALIDATION_GROUPS_KEY, UIInput.DEFAULT_VALIDATOR_IDS_KEY). These are used during later lifecycle phases (eg. BeanValidator.validate(), UIInput.encodeEnd()) to determine which inherited validators to apply and how these validators should be configured (eg. what validation groups to use). The end result of the f:validateBean solution is that the handlers only do part of the job - we need to do additional work during later lifecycle phases to take advantage of the information that has been stored away by the handlers. While these two different strategies may at first seem like implementation details, and thus not especially significant, the choice of implementation does have impact on both our API and on spec'ed behavior (or, on behavior that should be defined by the spec). In terms of API, for f:validateBean the choice of implementation leaks through a bit into the API in the form of the property keys that are used to communicate between the handler implementations and the component/validator implementations. In terms of behavior, the different implementation strategies and up with subtly different results which may cause confusion. For example, in the following f:ajax case: This should work as expected. That is, Ajax should be enabled for the "foo" inputText, but not for the "bar" input text. In a similar f:validateBean case: Unless I am missing something in the spec/implementation, I believe that the validation-related properties are going to end up being attached to the parent panelGroup when the BeanValidatorHandler is applied. Which, if I understand this correctly, means that the validation will be applied to both the "foo" and the "bar" inputText. If this is the case, this is definitely not the desired behavior. I suspect that similar problems would arise when we've got multiple <f:validateBean> under a single parent, eg: Though I haven't had a chance to test this out - just based on code inspection seems like this would be a problem. (Though our <f:ajax> implementation strategy handles this case just fine.) Since there may be other subtle inconsistencies, it would make sense to try to unify our implementation strategies across these two core tags. Of course, I am biased towards the <f:ajax> approach. Seems to have better behavior in terms of targeting only the wrapped subtrees, has less exposure in the public API, and also just seems cleaner to me to produce a fully configured component tree as a result of handler execution. Looking at the code, I didn't notice anything that would make it difficult to re-factor the <f:validateBean> code to use a handler-time strategy like <f:ajax>. I think our users would benefit from the consistency. Any thoughts on whether we should/can go this route? Did I miss anything in the <f:validteBean> behavior that would prevent us from using a handler-time solution? Andy