Servlets are the server side programs that runs on the server allow developer to add dynamic content and hand it to the web server and web server sent back to the client. Although servlets can respond to any type of request, they are commonly used to extend the applications hosted by Web servers. For such applications, Java Servlet technology defines HTTP-specific servlet classes. Servlets provide component-based, platform-independent methods for building Web-based applications, without the performance limitations of CGI programs.
The javax.servlet and javax.servlet.http packages provide interfaces and classes for writing servlets. All servlets must implement the Servlet interface, which defines life-cycle methods.

Typical uses for HTTP Servlets include :

    * Processing and/or storing data submitted by an HTML form.
    * Providing dynamic content, e.g. returning the results of a database query to the client.
    * Managing state information on top of the stateless HTTP, e.g. for an online shopping cart system which manages shopping carts for many concurrent customers and maps every request to the right customer.