| | | | | | Question Answer Tutorial - JAVA->SERVLET | | | | | | Question: 16.What is the use of servlet wrapper classes?
| | | Answer: Servlet HTTP API provides two wrapper classes – HttpServletR
equestWrapper and/>HttpServletResponseWrapper. These wrapper classes are provided to&nb
sp;help developers with custom/>implementation of servlet request and response types. We c
an extend these classes and override only/>specific methods we need to implement for custom request&n
bsp;and response objects. These classes are not/>used in normal servlet programming
| | | | | | | | | | | | Question: What is SingleThreadModel interface?
| | | Answer: SingleThreadModel interface was provided for thread safety and&nb
sp;it guarantees that no two threads/>will execute concurrently in the servlet’s service method.
;However SingleThreadModel does not solve/>all thread safety issues. For example, session attributes
and static variables can still be accessed/>by multiple requests on multiple threads at the same
time, even when SingleThreadModel servlets are/>used. Also it takes out all the benefits of multithre
ading support of servlets, thats why this/>interface is Deprecated in Servlet 2.4
| | | | | | | | | | | | Question: 18.Do we need to override service() method?
| | | Answer: When servlet container receives client request, it invokes t
he service() method which in turn/>invokes the doGet(), doPost() methods based on the HTTP&nb
sp;method of request. I don’t see any use case/>where we would like to override service() method. The
;whole purpose of service() method is to/>forward to request to corresponding HTTP method implementations
. If we have to do some/>pre-processing of request, we can always use servlet filte
rs and listeners
| | | | | | | | | | | | | Question: Is it good idea to create servlet constructor?
| | | Answer: We can define a constructor for servlet but I don’t&nbs
p;think its of any use because we won’t be having/>access to the ServletConfig object until unless servlet is
initialized by container. Ideally if we/>have to initialize any resource for servlet, we should&nbs
p;override init() method where we can access/>servlet init parameters using ServletConfig object. />
| | | | | | | | | | | | Question: What is difference between GenericServlet and HttpServlet?
| | | Answer: GenericServlet is protocol independent implementation of Servlet
interface whereas HttpServlet is/>HTTP protocol specific implementation. Most of the times w
e use servlet for creating web application/>and that’s why we extend HttpServlet class. HttpServlet cl
ass extends GenericServlet and also/>provide some other methods specific to HTTP protocol. />
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