[Cascavel-pm] Oak2, alguma documentação feita
Luis Campos de Carvalho
monsieur_champs em yahoo.com.br
Quinta Abril 7 11:47:42 PDT 2005
Foi apenas você quem não a recebeu, Daniel.
Eu prefiro ler a documentação no webbrowser, não no email.
Mas esta é uma preferência pessoal minha, sabe...
Parabéns pelo excelente trabalho!
Daniel Ruoso wrote:
> [enviei uma mensagem antes, fui só eu quem não recebeu da lista?]
> Olá tod em s,
> Estou tentando, aos poucos retomar o desenvolvimento do Oak2, e neste
> sentido elaborei um pequeno documento falando sobre os aspectos básicos
> do Oak2, no que se refere à Orientação a Objetos.
> Em cima disso vai ser desenvolvido todo o framework. Aí vai a
> documentação em anexo, que está no CVS do Oak, disponível em
> mas sempre com um delay enooooooorme...
> Oak2 Basics
> Hi, if you are reading this document it is probably because you are
> interested in Oak2 but you actually don't know exactly what is Oak
> neighter how it works.
> If this is the case, you are reading the correct document, this text
> exists to provide an introduction in how to use Oak2, how it works in a
> way you be able not only to use Oak2 to create your own applications,
> but also to contribute with components, toolkits and other things.
> Why Oak2?
> Well, it's named Oak2 because of its father project, Oak. Oak2 is a
> architectural revision of Oak.
> Ok, so why Oak?
> Two reasons, the first is that it is a three letter name, so it is easy
> to type. The second is that the oak tree has very very many branches,
> this applies to Oak. Oak is a tree of classes to support perl development.
> Duh, I was not asking about the name, but why does Oak exists?
> Ah... ok... Oak was created when I was on the team that was developing
> an ESP (email service provider) software infra-structure. And we
> realized that there wasn't any framework to help perl developers in an
> enterprise development. There weren't tools to handle data persistence
> (I mean more than DBI do), to handle authentication, authorization,
> business control, and even interface.
> When I started in web development with perl I did fill my cgi file with
> a lot of prints, to print the page I wish to show. Many people still do
> that way, and there's nothing wrong with it, but it just doesn't fit in
> an enterprise environment, you need much more low-cost maintainance,
> high customization and that's just impossible with prints into the cgi file.
> The first step forward was the use of Text::Template, in this way the
> cgi didn't need to have lots of prints anymore, just one. But that
> wasn't enough and we built an entire framework that made much easier all
> the work and made the maintainance much cheaper than before.
> But as we developed the framework while we were developing the
> application itself, the framework wasn't so perfect as we wanted to be.
> So this is why I started Oak in August 2001.
> Short answer: In a time we have frameworks like J2EE, like .net, like
> many others, it's necessary to give perl the power needed to be used in
> an enterprise environment. Oak exists to make the work of the
> application developer (not only script developer) easier.
> So, what was wrong with Oak that made necessary creating Oak2?
> There is one huge change and some minor changes. The huge change is a
> new aprouch to object oriented programming, that is including event
> handling, time sense and customization as fundamental parts of OOP, and
> in this way, Oak2::Object already does such things. Minor changes
> include changing prints in Oak::Web components for return. Better
> definition of Oak::Filer. Resolving inconsistencies, changing the way
> Components are seen inside Oak etc.
> Event Handling
> Events are an important part of Object Oriented Programming, specially
> when you're dealing with complex systems. For those who know database
> systems, this is very much like triggers, except that it can be applied
> to any object in any place (including Entity classes in Mysql).
> Just to illustrate, I'll tell when this can be usefull. You can add a
> event into a account payable in a way that when the account is paid it
> closes the order you made. Actually, the event mechanism is the key to
> create a integrated but not tied system.
> Time Sense
> The objects need to know that time is passing. I.e.: A due bill must
> know it's due so it can calculate how much must be paid because of the late.
> This is also usefull for some reality representations. I'll be
> explaining this better in other documents.
> P.S.: This isn't implemented yet, as I really still don't know how to
> make it nice.
> To explain this I'll use an example based on Java Swing API.
> Let's imagine you have a swing application. Now imagine you want to make
> the components to check into JAAS if the user has permission to see that
> component, and you want it applied to all components of your
> application. I.e.: Some text fields to be read-only or read-write
> depending on user's permissions.
> How would you do it?
> Create a subclass for each component you use implementing
> this feature
> Create a subclass for java.awt.Component and reimplement the
> entire swing
> Learn to use Aspect Oriented Programming.
> The Customization concept is very much alike AOP, but with an important
> difference. You don't have to say "execute before" or "execute later".
> You implement it as if you were implementing a subclass, with the subtle
> difference that instead of calling SUPER, you call ORIG. And you
> actually don't have to call ORIG, if you want to completely replace that
> method, you just do it.
> Enough of introduction, show it...
> Everything starts from Oak2::Object, this class defines:
> * How to instantiate an object
> * How the properties are handled
> * How events are handled
> * Error handling
> I'll talk about each of these topics in detail:
> How to instantiate an object
> Oak2::Object implements the method new that do all the required code to
> create an object in perl. This method calls the method constructor and
> after_construction that are responsible for initializing the object.
> In this way, nobody should implement the method new, but every object
> will be instantiated by the method new.
> Every class that wants to do something when initializing should
> implement the method constructor, but everytime you overload this method
> you must remember to call SUPER.
> And now a great difference from Oak 1. The introduction of the "restore"
> concept. At any time, it should be possible to store an object in some
> media (similar to object serialization in Java), and at any time it
> should be possible to restore that object in the state it was before
> storing. This is done with the Factory classes. One example of a factory
> class is the Oak2::XMLObjectFactory. But be carefull, each factory
> stores/restores an specific set of caracteristics, and you should pay
> attention when storing the object.
> The important thing in the restore concept is the Object Unique
> Identifier (objuid), this identifier is composed by the class factory
> that generated its output followed by a ; and the parameters to the
> factory. In the case you store an object using the XMLObjectFactory in
> the file obj.xml, the objuid would be
> 'Oak2::XMLObjectFactory;filename=obj.xml'. So, you can compose the
> objuid at any time if you know the information the factory needs. It
> will help you a lot in the future, believe me.
> How the properties are handled
> Oak2::Object implements the methods get, get_hash and set. This are the
> gateways to the object's properties. The method get can receive one or
> more parameters and will return as a list the values.
> The method get_hash is very similar to get (actually, the method get is
> a wrapper to get_hash) but instead of returning a list of values it
> returns a hash with the name of the property as the key and the value as
> the value.
> The method set is used to change the value of some property. It receives
> a hash with the properties being changed.
> How events are handled
> The events in Oak2 are very alike with the Java event infrastructure,
> but with some add-ons...
> The concept is that you have an object (or class) that fires events and
> you have listeners for these events. The big difference for the java
> infrastructure is that a listener can be of one of these types:
> execute METHOD on this object
> CODESTRING to be executed in eval. the return is the MD5 sum of the code
> OBJUID to be restored and then the METHOD to be called.
> object REF to be used to call the given METHOD
> Now, one by one:
> Self is a listener to be used by the same object or class that fires the
> event invoking some specific method.
> Static is a listener that is just some perl code in a string that will
> be eval'ed when the event is fired.
> Restorable is a listener of an object that should be restored before
> calling some specific method.
> And finally, dynamic is some object that wants some method to be invoked
> when the event is fired.
> Point to me, in Java you need to implement an specific interface to
> register yourself as a listener, here you simply say "hey, call this
> method in this object".
> The other conceptin the event handling is the event code. When
> registering a listener you should tell which event you're willing to
> listen to. The documentation for each class tells you which events are
> Error handling
> There is few to say here, because we just use the Error
> try/catch/otherwise/finally interface. Each class documents which Errors
> it throws.
> Moving on, now to Oak2::Component
> Wow, we finally saw the basic principles of Oak2 let's start to see more...
> The Oak2::Component class introduces the concept of some object own
> other object, I mean, some Component may have subcomponents, just that.
> If you see the documentation of Oak2::Component you'll see that it
> doesn't make much more than that. The important thing is that *every*
> component *must* have a name property setted.
> Daniel Ruoso <mailto:daniel em ruoso.com>
> Last modified: Wed Apr 6 18:37:42 BRT 2005
> Cascavel-pm mailing list
> Cascavel-pm em pm.org
Luis Campos de Carvalho is BSc in Comp Science,
PerlMonk [SiteDocClan], Sao Paulo PM Leader,
Unix Sys Admin && Certified Oracle DBA
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