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https://issues.apache.org/jira/browse/LABS-232?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14031880#comment-14031880
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jan iversen commented on LABS-232:
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Is this still an issue, if not please close it (or let me close it)
> [refactoring][beans] BeanData should be able to fork
> ----------------------------------------------------
>
> Key: LABS-232
> URL: https://issues.apache.org/jira/browse/LABS-232
> Project: Labs
> Issue Type: New Feature
> Components: Magma
> Affects Versions: Current
> Reporter: Simone Gianni
> Assignee: Simone Gianni
> Fix For: Next
>
>
> Currently every class has one BeanData. This class holds all magma specific
> metadata about the class, giving access to PropertyInfo for each property.
> That sums up introspection results, annotations and so on. Every package that
> needs to add stuff will do it adding it to BeanData or PropertyInfo.
> Also, all magma component communicate with the bean using a Handler. The
> Handler itself uses BeanData to perform property setting/getting, validation,
> formatting and the like.
> Anyway, having a single representation of a class is limiting. There is the
> need to change this data depending on the current context. For example, a
> certain field could be visible or not depending on the role of the current
> user, or the view we want to offer. Also validation could change, making some
> properties required where they where not, or even adding temporary
> properties. Information currently held in this structure is very wide, and
> goes from validation to formatting to structural data (like, if it is or not
> persisted on the database).
> Currently there is a system in place, called ViewCustomizer, which is able to
> modify dynamically part of it for a specific need, like hiding or expanding a
> property in a specific view. While this system works correctly, it cannot be
> expanded to also embrace validation, formatting and everything else. So we
> need a different approach.
> First of all, we need a way to "fork" different beanDatas, and provide a way
> to define which one to use in a specific "scope". The problem is not forking
> it (a deep clone is okay, prototype pattern), nor modifying the new "branch"
> (ViewCustomizer could be extended, giving it a further extensible API, and
> having people implement it). Defining the scope is a problem.
> Unfortunately in java the only thing that is "scope dependent" is the stack.
> So, we will probably have to pass the modified bean data, or the bean data
> modifier, instead of the class/bean where we need to.
> So, for example :
> return new SmartForm(new WiseModifier(userBean));
> To display a form using the WiseModifier. The WiseModifier class should be a
> class extending a specific base class, and implementing a specific method.
> For example :
> public class WiseModifier extends BeanDataModifier {
> public WiseModifier() {
> super(User.class);
> }
> public void modify() {
> makeRequired("name");
> addFormatter("birthDay", new DateFormatter().setFormat("short"));
> }
> }
> In this way, the modifiers will be classes, and as such (thru cglib
> eventually) compiler friendly and statically determined. Also, the non
> modified bean data could be obtained with a "null modifier", or simply still
> passing the Class object only (this would also provide backwards
> compatibility, keep the easy way, and provide an incremental way to implement
> this new system, cause new methods would simply be overriding the default,
> class based ones).
> It could also be possible, eventually using a CompoundModifier, to combine
> different modifiers. So, we could have a modifier that hides a certain part
> of a bean, another one that imposes a number of additional checks, and then
> use one, the other, or both in a certain context.
> Another important aspect could be caching of the resulting beanData. Creating
> a beanData is an expensive job, cause it involves reflection, annotation
> parsing, creation of a number of (mostly thread safe and stateless) objects
> like converters, formatters, validators etc..
> Since forking a bean data could be a lighter job (deep cloning as opposed to
> reparsing), proper investigation should be done on the effective timing of
> the deep cloning and manipulations. If caching is necessary, then a number of
> techniques could be exploited to obtain it.
> A modifier could a stateless one, thus applying always the same
> modifications. In that case, cache it and stop bothering.
> A modifier could have a state that is determinable. For example, a number of
> private fields, and a number of if statements based solely on those private
> fields. In this case, caching is still possible cause we know the state.
> A modifier could have a state which is not determinable, for example an if
> statement calling System.currentTimeMillis. In that case no caching is
> possible, and a proper warning should be given to the user.
> To limit the possibility of uncachable items, the API should be planned from
> the ground up with minimal connections to the outside world, or a predefined
> way of connecting to it, like getters and setters only, or constructor
> parameters only and so on.
> (Note that this is exactly what happens in every do-method of any web
> handler, in fact the same design principles were in place for the web API
> where caching plays an important role. Handlers have a predefined "protocol"
> with the outside world, thru getters and setters, making the state
> determinable in most cases. this means that the same caching system used in
> the web part could be applied to this part if needed)
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