Скачать или смотреть 9 Different Ways/Approaches to develop Servlet program|Adv Java Servlet programming Tutorial advance

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The three important resources of servlet API.
1. javax.servlet.Servlet (Interface)
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2. javax.servlet.GenericServlet (Abstract class)
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3. javax.servlet.http.HttpServlet (Abstract class)

• In Java an abstract class can contain only abstract methods or only concrete methods or mix of both.

• The above give predefined HttpServlet class is an abstract class containing no abstract methods.

• If you want to make methods / logics of one java class accessible only through subclass the make that class as abstract class even though that class contains only concrete methods.

servlet method inheritance (Diagram):

• Every servlet program is a java class that is developed based on servlet api.

There are three ways to develop servlet program.
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Approach 1:
Take a java class implementing javax.servlet.Servlet interface and provide implementation for all the five methods of that interface. (Compulsory to override all five methods)

Approach 2:
Take java class extending from javax.servlet.GenericServlet class and provide implementation for public void service(ServeltRequest, ServletResponse) method.

Approach 3:
Take java class extending from javax.servlet.http.HttpServlet class and override one of the seven doXxx() methods or one of the two service(- -) methods.
public void service(ServeltRequest, ServletResponse)
protected void service(HttpServeltRequest, HttpServletResponse)

• In the above said three approaches the overridden / implemented service(-,-) / doxxx(-,-) programmer places request processing logic that generates web pages by processing the request. But programmer never calls these methods manually but servlet container calls these methods automatically for every request given by client to servlet program.

• Programmer just supplies his servlet program related java class to servlet container then onwards servlet container is responsible to manage the whole life cycle of servlet program. (From object birth to death every operation will be take care by container).

• For all the request given to servlet program the servlet container creates one object but for every request given to servlet program, the servlet container create one separate request, response objects and calls service(-,-) method by keeping these requests, response objects as argument values.

Servlet-Object (Diagram):

• Servlet program uses request(ServletRequest or HttpSetveltRequest) object to read details from the client request(browser).

• Servlet program uses response(ServeltResponse or HttpServeltRespopnse) object to send response content/output/webpage to browser window through web server.

• When 10 requests are given to a servlet program from single or different browser windows (clients):
1) Servlet container creates 10 threads on servlet program objects representing 10 requests.
2) Servlet container creates 10 sets of request, response objects and calls service (-,-) or methods for 10 times having request, response objects as arguments values.

• To make our servlet program java class visible to servlet container the java class must be taken as public class.


The javax.servlet.Servlet Interface:
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The javax.servlet.Servlet interface is the basic interface of the Java Servlet API. This provides a standard abstraction for the servlet container to understand the Servlet object created by the user. That means the interface is designed to describe the user-defined Java object to the Servlet container, which encapsulates the application logic to plug into the servlet container for processing the client request. The servlet object must be a subtype of the interface to be manage