81 Why HttpServlet class methods are concrete methods, then why class is given as abstract class

Que. When all the methods of #javax.servlet.http.HttpServlet class are #concrete #methods, then why the class itself is given as #abstract #class? #Advance #Java #Servlet #Programming #Tutorial
Ans : In java abstract calss can have only abststract methods or only concrete methods or mix of both methods. To allow logics of java class accessing only through sub classes then the java class will be taken as abstract class even though that class contains only concrete methods.

- javax.servlet.http.HttpServlet class is abstract, even though none of the methods with in it are abstract its because, it contains seven doXxx(-,-) methods, to match seven ways of making HTTP requset (GET/POST/DELETE /PUT / OPTIONS / TRACE /HEAD). These methods are the request processing methods of HttpServlet class, just like service(-,-) method in GenericServlet.

- Since there is only one requst-processing method for GenericServlet and it is defined as abstract in javax.servlet.GenericServlet class, which makes the developer/programmer making his class to extend from javax.servlet.GenericServlet class, to provice implementation only for one method i.e. (public void service(SReq,SRes)).

- but in the case of javax.servlet.http.HttpServlet class, if all seven+2 (seven doXxx, two service methods)are defined as abstract, then every developer/programmer who create the a child class(our servlet) of HttpServlet class, has to provide implementation for all the seven+two methods, which is quite an issue. So the specification has made by javax.servlet.http.HttpServlet class to contains implementaions for all the seven+two methods, but made the javax.servlet.http.HttpServlet class itself as abstract class, means no developer can create an instance/object of HttpServlet class directly and logics of HttpServlet class will be accessed only through Sub classing.


Note : A good programmer overrides init() method for keeping initialization logic & overrides doGet(-,-), doPost(-,-) method for keeping request processing logic while developing servlet program.

when we override init() method in our servlet program, there is no need of initializing ServletConfig object manually