Monday, January 20, 2014

Introduction to Web Applications Part-II


We already know web application can be categories into two types
  1. Static web applications
  2. Dynamic Web Applications

Go through following links to web application introduction part  I

Static Web Applications

A static web application deliver response to user what exactly stored in server. The response is always same for all users when they requested to server. It means static html pages, pdf files and images.

These resources are available in server so that when the user requested to server and the server will serve as response. The user will be requested as simple http request to the server so that server will serve the static recourses as response. To handle request and manage these recourse we will use web server.

What is web server?

A web server is server to handle or process the http request and serve the response to the end users.

We already know http request is simple URL and it will ask the web server for response on behalf of user.

The popular web server in the market is Apache Web Server. In the world most of the web servers are Apache Web servers

For example we will request for one html page that html page contains the company information.

When we send above request to the web server it will always give the static data which is presented in requested html page. It means the response data always same for all user requests.

The following is more information about Apache Http server

The final bottom line is static web applications always serve same response to users and to manage these static web applications we will use web servers.

Dynamic Web Application

Dynamic web application serves the response based on user demand and the response is varying based on user request.

It will generate dynamic response to end user when they request to the server. Here http request is same but based on user the content/data will be changed.

For example it will use same resource for every request but the resource will be generating the dynamic content based on user request.

We can assume we want employee information and for this each request we call same resource but it will give different employee information

If we observe above request, based on employee Id we will get different employee information but each time it will execute same resource in server.

The following diagram shows the web application in server

In above diagram user send the request to get employee information and server execute same resource and that recourse get employee data from information system and give response back to the user.

Who will produce Dynamic Response?

In dynamic web applications to produce dynamic response we need special kind of resources and these resources are called helper applications.

Helper application are kind of recourses will be executes in server to prepare dynamic response. To execute helper applications we need containers.

Helper application is server side technology to produce dynamic response based on users demand.

What is container?

Containers are managing helper applications it means it will process helper application to produce dynamic response. Processing of helper application is like execution of helper applications.

Containers are responsible for managing liferay cycle of helper application when they producing dynamic response. The example for helper application in Java is servlet

Servlet is helper appellation or server side component to produce dynamic request to the user.
To execute servlet we need servlet container. The servlet container is responsible for execution of servlet or manages the life cycle of servlet when they produce dynamic request.

We have different containers in java like servlet container, EJB container and JMS container.
Static Web application can be served by Web servers but dynamic applications cannot so that dynamic web application needs application servers.

What is Application Server?

Application server is like web server to handle http request besides that it will also manage the dynamic applications.

We already know to execute dynamic application we need containers. Application server has ability to integrate with many containers like servlet, EJB and JSM containers.

Application server is used to manage dynamic web application.

We already know we need helper application or servlet to process dynamic request. To produce dynamic response it will use some information system for getting the data. Those information systems are like databases.

Servlet need database to produces dynamic response. The response is in the form of browser understandable language that is html.

Servlet can produce response in the form of HTML or other formats like text, images and files formats but all these formats should understand by browser.


In the real environment we will use combination of Web server and Application Server

General Request flow in Dynamic Web application
  • The user/client sends the request to the server.
  • Server will identify the request whether it is dynamic request or static request.
  • If static request then web server handle the request means it will process request and produces the response.
  • If dynamic request then web server delegates the request to helper application so that helper application processes the dynamic request and it will generate the response. Helper application will take the container help to produce the response.
  • The response will give to the web server and web server is responsible to send response to client.

The following diagram depicts the flow of dynamic request.

In java we will use servlet to process dynamic request and we use servlet to build dynamic web applications.

What is servlet?

Servlet is server side technology to produce dynamic response. Servlet will be executed in servlet containers when they produce dynamic response. Servlet container will manage the lifecycle of servlet.

Important Points
  • We have two different kinds of web applications static and dynamic.
  • Static application will be managed by web servers and dynamic applications are managed by application server.
  • To produce dynamic response we need helper applications and these helper application need container to execute and produce response.
  • Helper application is server side technology and example in java is servlet.
  • Application server has ability to accommodate different container like servlet, EJB and JMS containers.
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