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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Types of Applications developed by using Java language.

Below Diagram shows clear explanation

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Basic Operations to performed in java application

Using only programming language we performs three operations in developing logic.

1. Reading and Storing input data.
2. Doing calculations for modifying data and generating output.
3. Controlling modifications.
4. Storing output permanently or printing it on console.

To perform first three operations every programming language contains three concepts.

1. Datatypes: used to store data temporarily.
2. Operations: For doing calculations.
3. Control Statements: Used for validating and controlling modifications.

In edition 2 above three concepts we also has more concepts to perform below tasks.

1. Reading input values from end user : IO Streams/ AWT.
2. Sending multiple values at a time to another application : Arrays and Collections .
3. Processing all requests at a time concurrently : Multi Threading .
4. Handling user mistakes and user understandable message : Exception Handling.
5. Sending and Reading data from Networking : Networking.
6. Storing data or output permanently : IO Streams and JDBC.
7. Executing logic in server system via web protocol : Servlets or JSP.
8. Executing logic in server system via distributed protocols : RMI and EJB.
9. Organizing logic Development by making it reusable from multiple applications by writing single program to execute method from different sub classes of an object : OOPS , LCRP , MVC.

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Welcome To JavaTCup

I am Harishkumar Reddy ,Started this blog to share my knowledge to this world as my level best.Many of the students, they are struggling to explain the exact answer in interview.I will give clear explanation on every topics as my Knowledge.In this blog i am going to explain core java , Jdbc, Servlets ,JSP Servlets ,Oracle ,My Sql ,HTML ,CSS and many more we will update soon.Thank you.

Harishkumar Reddy

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