What is Servlet ?

• Servlet is a server side executing program (Components).
• Servlet is also a specification it is given part of J2EE frame work. J2EE has three specifications.

                       1.Servlet

                       2.JSP Servlet

                       3.EJB

• Servlet and JSP Specification are given to develop web applications.
• EJB specification is given to develop enterprise distributed application.
• A Specification is a set of rules and guidelines for developing either a single program or Software.
• J2EE specification (Servlets . JSP , EJB) gives rules and guidelines for developing server Software and web and enterprise applications.
• J2EE specification is given by sun microsystem.
• Server Software are implemented by following three specifications by different venders.
• A test server Software is also implemented by Sun Micro System.

          Some of the well known server software

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• Java programmers as part of project development develops web and enterprise application s by following J2EE specification.
• specification contains interface with method declarations.

                          --> These interfaces are given by sum micro systems.

                         --> These interfaces are implemented by deriving sub classes by

                                             --> Server vendars for server software development.

                                             --> By java programmer for project components development.

• J2EE specification it is not program or software . it is a just a document file (word doc , pdf file). So we can not use it from java program as it is not available in java Syntax file.
• It is a server vendor  responsibility to develop the specification as java .classes and interfaces compile them and should distribute to the word as work jar files.

• Now as a project developer we must install one server software in our computer to availe j2ee-api (servlet , Jsp , EJB).classes files.
• Then after installing server software we must set Classpath with jar file path to use J2EE specification classes from our java program.
• If we don't set jar file in Classpath in compiling java program we will get compile time error package javax doesn't exit.
• Java EE specification classes and interfaces are given in javax package and their implementation classes will be given in vendor specific package.

                   EX: org.apache

• So we must import javax package in our program not vendor given package.
• If we use vendor given package our program can not executed in another vendor given sever software.

Bellow diagram shows J2EE specification implementation with all above points

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Posted in: advanced java, servlets