Hi,
Michael Gasche wrote:
> Hello
>
> This Email refers to the first Email of the 'case studies' series. I may
> look at things less politically in building a webarchitecture for
> transactions. And actually this is what most of us want at least: Storing
> and serving data from a database and hopefully using some intelligent
> middleware which does OR-Mapping, gives high availability and
> performance...etc.
>
> Performance, one important point. The last tier in Webarchitecture mostly
> is a relational DB. So, whatever you're using or programming, there are
> usually SQL-Statements and somekind of hardware which stores or provides
> data as fast as this hardware and software is for this DB. I don't even
> want to talk about the performance of JBoss. It is high.
>
> Now, you may look for an alternative for EJB. What you want to use? Sure,
> maybe you're building a Webarchitecture like a MVC-2-Model. Where should
> placed the scalability? Then you program kind of intelligent pooling for
> connections to the DB, pooling for the data in the DB (Datatree or so..).
> Then you may implement an intelligent OR-Mapping and a SQL-Server for
> default SQL-statements all this features are maybe placed in JavaBeans and
> other strutures.
>
> What you've done? You actually implemented almost (there's are still more
> features of course) everything which defines a EJB-Server whitout looking
> at the EJB-Specs! So, why don't use EJB? One thing is for sure: the
> maintance for the written code is a lot more higher. And code need to be
> maintanced. Or we want to have more functionality: add some entity or
> session beans and everything's done. That's where the MVC-3-Model starts.
>
Well, no, you haven't come close to implementing ejb spec at all. In an
earlier post I mentioned a very similar architecture and that it was
successful. But look beyond the representation of data in a database as
objects and your ability to get and set values on those objects. Using ejb
buys you the ability to use those data objects whether they are living on
the same hardware as your servlet or on a box on the other side of the
world -- a true *enterprise* app. So for one thing the remote interfaces and
distributed objects are *not* available in the "MVC-2 Model" you spoke of.
Also missing are things like ejb activation and passivation which are *very*
important; without them your java business objects get stuck in memory until
they are no longer referenced, rather than making room for more recently
used entities, for instance. Of course there's more. So ejb is much more
powerful than the mvc-2 thing. But you may choose to use a model as you
state to simplify and speed development. While there are issues with code
maintanance there are always trade offs. For sure ejbs take longer to
develop than simple java business objects, and if the project you are
working on cannot justify that overhead (maybe not *really* and enterprise
app) then you might choose to go home early/ier at night :-)
> Not to long ago I helped to build the following architechture:
>
> MVC-2: JSP/Servlets<-->JavaBeans<-->DB-Logic<-->Database
>
> If you have done something like that too and you know what EJB is able to
> do for you, and of course you're using a good EJB-Server like JBoss then
> next time or in future you will use EJB.
Maybe, if it's the right choice for the project -- high scalability and
enterprise bound. Or are we thinking, hey, ejb invoices higher than without?
In that case someone might say, 'sure, let's do ejb!' ;-)
>
> regards,
> Michael Gasche
Cheers,
Vaughn
>
>
>
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