- 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 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.
- 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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