Answer / ravi v v

Pleae find an Example for the above one.

An example
As an example, consider an online store that provides real-
time pricing and availability information. Most likely, the
site will provide a form with which you can choose a
product. When you submit your query, the site performs a
lookup and returns the results embedded within an HTML
page. The site may implement this functionality in numerous
ways. I'll show you one scenario that doesn't use an
application server and another that does. Seeing how these
scenarios differ will help you to see the application
server's function.

Scenario 1: Web server without an application server

In the first scenario, a Web server alone provides the
online store's functionality. The Web server takes your
request, then passes it to a server-side program able to
handle the request. The server-side program looks up the
pricing information from a database or a flat file. Once
retrieved, the server-side program uses the information to
formulate the HTML response, then the Web server sends it
back to your Web browser.

To summarize, a Web server simply processes HTTP requests
by responding with HTML pages.

Scenario 2: Web server with an application server

Scenario 2 resembles Scenario 1 in that the Web server
still delegates the response generation to a script.
However, you can now put the business logic for the pricing
lookup onto an application server. With that change,
instead of the script knowing how to look up the data and
formulate a response, the script can simply call the
application server's lookup service. The script can then
use the service's result when the script generates its HTML
response.

In this scenario, the application server serves the
business logic for looking up a product's pricing
information. That functionality doesn't say anything about
display or how the client must use the information.
Instead, the client and application server send data back
and forth. When a client calls the application server's
lookup service, the service simply looks up the information
and returns it to the client.

By separating the pricing logic from the HTML response-
generating code, the pricing logic becomes far more
reusable between applications. A second client, such as a
cash register, could also call the same service as a clerk
checks out a customer. In contrast, in Scenario 1 the
pricing lookup service is not reusable because the
information is embedded within the HTML page. To summarize,
in Scenario 2's model, the Web server handles HTTP requests
by replying with an HTML page while the application server
serves application logic by processing pricing and
availability requests.

Answer / ravi v v

Here you go:

-------------------
The Web server:
-------------------
A Web server handles the HTTP protocol. When the Web server
receives an HTTP request, it responds with an HTTP
response, such as sending back an HTML page. To process a
request, a Web server may respond with a static HTML page
or image, send a redirect, or delegate the dynamic response
generation to some other program such as CGI scripts, JSPs
(JavaServer Pages), servlets, ASPs (Active Server Pages),
server-side JavaScripts, or some other server-side
technology. Whatever their purpose, such server-side
programs generate a response, most often in HTML, for
viewing in a Web browser.

Understand that a Web server's delegation model is fairly
simple. When a request comes into the Web server, the Web
server simply passes the request to the program best able
to handle it. The Web server doesn't provide any
functionality beyond simply providing an environment in
which the server-side program can execute and pass back the
generated responses. The server-side program usually
provides for itself such functions as transaction
processing, database connectivity, and messaging.

While a Web server may not itself support transactions or
database connection pooling, it may employ various
strategies for fault tolerance and scalability such as load
balancing, caching, and clustering—features oftentimes
erroneously assigned as features reserved only for
application servers.
----------------------------
The application server:
----------------------------
As for the application server, according to our definition,
an application server exposes business logic to client
applications through various protocols, possibly including
HTTP. While a Web server mainly deals with sending HTML for
display in a Web browser, an application server provides
access to business logic for use by client application
programs. The application program can use this logic just
as it would call a method on an object (or a function in
the procedural world).

Such application server clients can include GUIs (graphical
user interface) running on a PC, a Web server, or even
other application servers. The information traveling back
and forth between an application server and its client is
not restricted to simple display markup. Instead, the
information is program logic. Since the logic takes the
form of data and method calls and not static HTML, the
client can employ the exposed business logic however it
wants.

In most cases, the server exposes this business logic
through a component API, such as the EJB (Enterprise
JavaBean) component model found on J2EE (Java 2 Platform,
Enterprise Edition) application servers. Moreover, the
application server manages its own resources. Such gate-
keeping duties include security, transaction processing,
resource pooling, and messaging. Like a Web server, an
application server may also employ various scalability and
fault-tolerance techniques.

Cheers
Ravi V V
Capita

Answer / guest

The basic difference between a web server and an application
server is
Webserver can execute only web applications i,e servlets and
JSPs and has only a single container known as Web container
which is used to interpret/execute web applications
Application server can execute Enterprise application, i,e
(servlets, jsps, and EJBs) it is having two containers 1.
Web Container(for interpreting/executing servlets and jsps)
2. EJB container(for executing EJBs). it can perform
operations like load balancing , transaction demarcation etc
etc

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