Servlet interview questions, Servlet Questions, answer, question, servlet

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Servlet Question 1. Can a Java Thread be started from Servlet class, and what will be the implications? Servlet Answer : Yes, it is possible to write a Thread or start a Thread from Servlet. In fact a Servlet can be started on load of the web application by defining "load-on-startup" tag value as "1" in the "web.xml" file. One should not start/create a thread from a Servlet that is to be invoked by browser or Java client application. Reason is that web container has Threads running to delegate every client request to appropriate Servlet instance. If servlet instance starts a thread from every request, then it is like each thread spanning multiple threads. As HTTP is stateless protocol, and after response is sent back to client, job of servlet is over, and web container manages the lifecycle of the servlets, but not responsible for the lifecycle or management of the Threads those Servlets have created. If need is to to some kind of scheduling operation, then it is allows advisable to try for some good Scheduler frameworks available. Servlet Question 2. What is HTTP Session tracking and why is it important? Servlet Answer : HTTP Session tracking is the way Web server knows that the request is not a fresh or new request, and has a session already created in the web context. So when a request reaches web server, it looks for a variable called jsessionid, that should be associated with the request either in form of cookies, or URL rewriting. If your site visitor has blocked all cookies then redirect to another JSP or Servlet, will not be able to carry the same session, and all the data/object reference stored in HttpSession is/are lost. But is this redirect is done by using encodeURL method of HttpServletResponse object, then session id is attached as a part of URL and webserver attaches already created session to the new request. Servlet Question 3. What is session management, and how is it different from session tracking? Servlet Answer : HTTP session management is related to the mechanism, by which application data or client state can be passed from one request to another request (As HTTP is stateless). Session Management is obviously comes after session tracking, as without session tracking, client request cannot be hooked onto one and only one session. But if requirement is to just pass reasonably small data/variables, from one request to another, then it can be done, by Hidden form field, and can be transported from browser to server, either by POST or GET as method in HTML FORM tag. Servlet Question 4. Can I use Hidden form field to track session? Servlet Answer : No, as Hidden form field sends its value as a request parameter, which is not same as URL rewriting (passing jsessionid as part of URL). Servlet Question 5. How can I pass method as request parameter to be called, instead of default doGet or doPost method of HttpServlet object, on submit of an URL?

Servlet Answer : By overriding service method of HttpServlet object, and using reflection to invoke the desired method of the servlet that is passed as a request parameter. It is similar to the dispatcher mechanism implemented in Struts framework for dynamic dispatching of action. Servlet Question 6. In a architecture pattern like MVC, it is mandatory that Servlet should be the controller, why not JSP? Servlet Answer : As JSP cannot be configured as a default mapping to be called based on a URL pattern in web.xml file. In that case, not all request goes through a JSP controller, and the very purpose of controller is not achieved. As Servlet can be mapped to a particular URL in web.xml like, <servlet-mapping> <servlet-name>SampleController</servlet-name> <url-pattern>/*</url-pattern> </servlet-mapping> Servlet Question 7. Why JSP is used as View part of MVC ? Servlet Answer : As JSP is easily configurable at runtime and by using Tag library, XSL, and many more scripting language, productivity increases by using JSP instead of Servlet. Servlet Question 8. Can a database connection pool be instantiated in init method of servlet instead of server connection pool? What will be the problem? Servlet Answer : It is true that connection pool can be instantiated in init method of Servlet and is available for the web application to use, but generally there can be many web application required to use database connection pool, and multiple web applications do not have access beyond ServletContext.So it is desirable to have external resources defined at server level, not at an application level. Servlet Question 9. How to implement Servlet singlethread model, by not using singlethreadmodel? Servlet Answer : Please write your understanding on this Servlet Question.

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