Web applications

[John Amos]

Hi you web gurus
I am from the old client server world and am moving into web application
development . I am trying to understand the architecture of web based applications
( with webservers , appservers , Java , EJB etc) by making analogies to the
client server env. Can someone direct me to some good websites or books
which will help me understand the architecture of web applications and how
the different components work . Like why do you need an application server
? or how does a java program or a java servlet get invoked from a web page
?

Thanks

[MarkN]

John,
You can use these tools to do C/S applications too. The architecture of
"web" apps can very depending on needs, environment and who is doing it.
I'll try to stay off the soap box and just answer the question - like I
use the term "distrubuted" applications instead of "web", "b-to-b", "e-commerce",
etc.

Anyway ...
A webserver is an application that servers up html pages or handles incoming
http requests and directs them to the proper app. It can also be a computer
that hosts a webserver app.

An appserver is a host application for EJB's, servlets, JSPs, does connection
pooling, etc. It allows "programs" to run server side.

Java is a language whose code can run on any platform that has a JVM written
for it (Mainframe to mobile phone). You can create applets, servlets, EJBs,
Javabeans, "programs", etc.

Each piece of a distributed app is like a mini c/s app. You have a client
and an server. The client might not have a visual interface. A server could
have different kinds of clients and clients can use different kinds of servers.
The point of this to make it flexible. You can have the whole application
running on one machine(including client) or n-machines.

I could list a whole lot of different application configurations. Let me
know if you want me to list some.

As for other info, there is a lot on the web. O'Rielly and WROX have good
books and there are others.

Check out IBM's site - http://www-106.ibm.com/developerworks/

Mark


"John Amos" <john_amos@hotmail.com> wrote:
>
>Hi you web gurus
> I am from the old client server world and am moving into web application
>development . I am trying to understand the architecture of web based applications
>( with webservers , appservers , Java , EJB etc) by making analogies to
the
>client server env. Can someone direct me to some good websites or books
>which will help me understand the architecture of web applications and how
>the different components work . Like why do you need an application server
>? or how does a java program or a java servlet get invoked from a web page
>?
>
>Thanks

[Aaron Sevivas]

In addition,

A multi-layered application (n-tier) was originally designed to separate
program logic. The 2-tier client-server app usually has a data tier and
a client. This architecture can be very hard to maintain, can be very hard
to scale, and very hard to extend if the application starts to grow. An
n -tier app would have multiple layers, as an example:

presentation layer: maybe a java client or html pages (presentation client
would be the browser, presentation layer would be the web server in some
architectures)
implemented: you name it! (Most common way is using a web server for business
apps, heavy (not a web browser) socket/RMI/COM clients)

(Recent Addition)ChannelLayer: This layer contains components which contain
code related to specific channels such as mobil WAP devices, HTML, a heavy
java or VB client.
implemented in: servlets||EJB||COM

BusinessLayer: Contains any business specific code, often broken up into
two layers, for example BusinessLayer/CommonBusinessLayer.
implemented in: servlets||EJB||COM

INTEROP Layer: This layer contains code which may be needed to "talk" to
different back-end systems. For example you may have multiple database systems
from different vendors.
implemented in: servlets||EJB||COM

Data Layer: Your data source (Oracle,MSSQL,ANYSql,a text file..)

I hope this helps a little and you see the benefits in this type of coding.
The key is "Don't be intimidated by new development techniques!" They were
made by gifted monkeys like yourself!

~aaron

"MarkN" <mnuttall@nospam.com> wrote:
>
>John,
> You can use these tools to do C/S applications too. The architecture
of
>"web" apps can very depending on needs, environment and who is doing it.
> I'll try to stay off the soap box and just answer the question - like I
>use the term "distrubuted" applications instead of "web", "b-to-b", "e-commerce",
>etc.
>
>Anyway ...
>A webserver is an application that servers up html pages or handles incoming
>http requests and directs them to the proper app. It can also be a computer
>that hosts a webserver app.
>
>An appserver is a host application for EJB's, servlets, JSPs, does connection
>pooling, etc. It allows "programs" to run server side.
>
>Java is a language whose code can run on any platform that has a JVM written
>for it (Mainframe to mobile phone). You can create applets, servlets, EJBs,
>Javabeans, "programs", etc.
>
>Each piece of a distributed app is like a mini c/s app. You have a client
>and an server. The client might not have a visual interface. A server
could
>have different kinds of clients and clients can use different kinds of servers.
> The point of this to make it flexible. You can have the whole application
>running on one machine(including client) or n-machines.
>
>I could list a whole lot of different application configurations. Let me
>know if you want me to list some.
>
>As for other info, there is a lot on the web. O'Rielly and WROX have good
>books and there are others.
>
>Check out IBM's site - http://www-106.ibm.com/developerworks/
>
>Mark
>
>
>"John Amos" <john_amos@hotmail.com> wrote:
>>
>>Hi you web gurus
>> I am from the old client server world and am moving into web application
>>development . I am trying to understand the architecture of web based applications
>>( with webservers , appservers , Java , EJB etc) by making analogies to
>the
>>client server env. Can someone direct me to some good websites or books
>>which will help me understand the architecture of web applications and
how
>>the different components work . Like why do you need an application server
>>? or how does a java program or a java servlet get invoked from a web page
>>?
>>
>>Thanks
>