Servlet to develop the

web application dynamically

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Servlet is used to develop the web application ( web application resides at server side and creates dynamic web page).

There are many interfaces and classes in the servlet API such as Servlet, GenericServlet, HttpServlet, ServletRequest, ServletResponse etc.

Before Servlet, CGI (Common Gateway Interface) scripting language was used as a server-side scripting language.

But CGI was having many disadvantages .

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CGI technology enables the web server to callan external program and pass HTTP requestinformation to the external program to processthe request.

For each request, it needs to start a newprocess.

CCGI(Common Gateway Interface)

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Disadvantages of CGI

1) If number of clients request increases, it takes more time for sending response.2) For each request, it needs to start a process and Web server is limited to start processes.3) It uses language which are platform dependent for example C, C++, perl.

What is Servlet ?

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What is Servlet

- Servlet is a technology which is used to create web application.- Servlet is an API(Application Programming Interface) which gives many interfaces and classes including documentations.

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- Servlet is an interface that must be implemented for creating any servlet.- Servlet is a class that extend the capabilities of the servers and respond to the request. - Servlet is a web component which is deployed on the server to create dynamic web page.

Advantages of

Servlet

1.Good Performance: because it creates a

thread for each request .

2.Portable:because it uses java language.

3.Robust:Servlets are managed by JVM so we don't

need to worry about memory leak , garbage collection etc.

4.More Secure:because it uses java language..

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Servlet Life Cycle

A servlet life cycle can be defined as the entire process from its creation to the destruction. The following are the ways followed by a servlet

- The servlet is initialized by calling the init () method.

-The servlet calls service() method to process a client's request.-The servlet is exit by calling the destroy() method.-Finally, servlet is garbage collected by the garbage collector of the JVM.

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The init() method :The init method is invoked only once. init() is

invoked when the servlet is first created, and not invoked again for each user request. So, it is used for one-time initializations.

The init() method creates or loads some data that will be used throughout the life of the servlet.

The service() method :The service() method is the main method to perform the task. The servlet container (i.e. web server) calls the service() method to handle requests coming from the user ( browsers) and to write the formatted response back to the user.

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The destroy() method :The destroy() method is called only once at the end of the life cycle of a servlet.

This method gives servlet a chance to close database connections, halt background threads, write cookie lists or hit counts to disk, and perform other such cleanup activities.

Use of Servlet

1) To accept form input and generate HTML Web pages dynamically.2) As part of middle tiers in enterprise networks by connecting to SQL databases via JDBC.3) In conjunction with applets to provide a high degree of interactivity and dynamic Web content generation.

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4) Servlets could act as active agents which share data with each other.5) Servlets could be used for balancing load among servers 6) Protocol support

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