Why the HttpServlet class is an abstract?

Question

I am very confused. Why the HttpServlet class is an abstract? And what is the basic difference between bean and pojo?

I've moved the title to your question body. In future, always include the question in the body. Else you might not get a good response. — Rohit Jain, Feb 21 '14 at 17:33
Duplicate of http://stackoverflow.com/questions/18909206/why-httpservlet-is-an-abstract-class-any-functional-reason — Abimaran Kugathasan, Feb 21 '14 at 17:34
Your bean/pojo question is an entirely different question, and should be asked in a different post (if at all). — Jon Skeet, Feb 21 '14 at 17:35
Would you ever need instance of `HttpServlet`? How would you use it? — Pshemo, Feb 21 '14 at 17:35
Duplicate of http://stackoverflow.com/questions/6742533/why-httpservlet-class-is-declared-as-abstract for the first question — developerwjk, Feb 21 '14 at 17:35
Duplicate of http://stackoverflow.com/questions/1612334/difference-between-dto-vo-pojo-javabeans for the pojo/bean question — developerwjk, Feb 21 '14 at 17:37

score 2 · Answer 1 · answered Feb 21 '14 at 17:36

HttpServlet is abstract because it's completely useless without concrete implementations of the business methods. The javadoc says:

Provides an abstract class to be subclassed to create an HTTP servlet suitable for a Web site. A subclass of HttpServlet must override at least one method, usually one of these:

doGet, if the servlet supports HTTP GET requests

doPost, for HTTP POST requests

doPut, for HTTP PUT requests

doDelete for HTTP DELETE requests

init and destroy, to manage resources that are held for the life of the servlet

getServletInfo, which the servlet uses to provide information about itself

Bean and Pojo are terms that usually refer to simple java classes that do not implement interfaces or extend classes from external libraries/frameworks.

score 1 · Answer 2 · answered Feb 21 '14 at 17:34

Why would HttpServlet not be abstract? An instance of just HttpServlet would be useless - the whole point of a servlet is to be able to provide useful responses to requests, and HttpServlet can't do that. It's generally a good idea to prevent useless situations where possible.

As another example of something similar, consider MouseAdapter. That's abstract despite having no abstract methods, because it's useless until you override at least one method.

score 1 · Answer 3 · answered Feb 21 '14 at 17:36

Check the API

Provides an abstract class to be subclassed to create an HTTP servlet suitable for a Web site. A subclass of HttpServlet must override at least one method, usually one of these:

doGet, if the servlet supports HTTP GET requests

doPost, for HTTP POST requests

doPut, for HTTP PUT requests

doDelete, for HTTP DELETE requests

init and destroy, to manage resources that are held for the life of the servlet

getServletInfo, which the servlet uses to provide information about itself

HttpServlet does not have useful functionality on its own.

thank you for your response.But my question is "if there is no any abstract method present in HTTP servlet class(means we have to override all methods) then why it is called ABSTRACT class?" — Aizen, Feb 25 '14 at 10:10

Why the HttpServlet class is an abstract?

3 Answers3