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Servlet interview questions

  • Exception handling in Servlet and JSP specifications view answer
  • Details about load on startup (load-on-startup tag) in Servlet ? view answer
  • What's the difference between init() & init(ServletConfig) and Which is better ? view answer
  • Servlet Life Cycle ? view answer
  • Q. Can we override init() or init(ServletConfig) method of HttpServlet ? Which is better ? view answer
  • Q. Can we override service method in HttpServlet ? view answer
  • Q.What is the difference between init() and init(ServletConfig) ? view answer
  • Q.How to upload an File/image from servlet/jsp into server from clients machine? view answer
  • What's the difference between init() & init(ServletConfig) in genericServlet ? view answer
  • Q.What is the difference between ServletContext and PageContext? view answer
  • Q.What is the difference in using request.getRequestDispatcher() and context.getRequestDispatcher()? view answer
  • Q.Difference forward() and response.sendRedirect() . view answer
  • Q.Can we use the constructor, instead of init(), to initialize servlet? view answer
  • Q.Explain the life cycle of Servlet? view answer
  • Q.Why don't we write a constructor in a servlet? view answer
  • Q.When we don't write any constructor for the servlet, how does container create an instance of servlet? view answer
  • Q.Why is it that we can't give relative URL's when using ServletContext.getRequestDispatcher() when we can use the same while calling ServletRequest.getRequestDispatcher()? view answer
  • Q.Once the destroy() method is called by the container, will the servlet be immediately destroyed? What happens to the tasks(threads) that the servlet might be executing at that time? view answer
  • Q.Request parameter How to find whether a parameter exists in the request object? view answer
  • What is new in ServletRequest interface ? view answer
  • Q.Given the request path below, which are context path, servlet path and path info? /bookstore/education/index.html view answer
  • Q.When a client request is sent to the servlet container, how does the container choose which servlet to invoke? view answer
  • Q.What is servlet container? view answer
  • Why IllegalStateException in jsp/servet? view answer
  • Q.How do I upload a file in a servlet app? view answer
  • Q.What's the difference between response.sendRedirect() and requestDispatcher.forward() ? view answer
  • Q.How do I implement security for my web application ? view answer
  • Q.How can I use servlets with protocols other than HTTP, e.g. FTP? view answer
  • Q.What happens if i call destroy() from init()? view answer
  • Q.Why can't a container call constructor having parameters? view answer
  • Q.Why do servlets have an init method? Can't we make use of the servlet constructor for initialization? view answer
  • Q.Explain the life cycle methods of a Servlet. view answer
  • Q.Explain the directory structure of a web application view answer
  • Q.What are the common mechanisms used for session tracking? view answer
  • What is load-on-startup in servlet ? view answer
  • Q. What is the difference between the getRequestDispatcher(String) and getNamedDispatcher(String) methods in the ServletContext Class? view answer
  • Q: What is the difference between Difference between doGet() and doPost()? view answer
  • Q. What is the difference between ServletContext and ServletConfig? view answer
  • Q: What is the difference between HttpServlet and GenericServlet? view answer
  • Q.What is the difference between the getRequestDispatcher(String path) method of ServletRequest interface and ServletContext interface? view answer

!!! Servlet interview questions !!!

Q. Can we override init() or init(ServletConfig) method of HttpServlet ? Which is better ?



Before start we have to understand the servlet flow.
For example you have servlet LoginServlet which extends HttpServlet
public class LoginServlet extends HttpServlet{
}
And your HttpServlet internally extends GenericServlet.

public abstract class GenericServlet
implements Servlet, ServletConfig, Serializable
{

public GenericServlet()
{
}
public void init()
throws ServletException
{
}
public ServletConfig getServletConfig()
{
return config;
}
public void init(ServletConfig config)
throws ServletException
{
this.config = config;
init();
}

public abstract void service(ServletRequest servletrequest, ServletResponse servletresponse)
throws ServletException, IOException;

private transient ServletConfig config;
}


Now servlet container flow

Step 1. Loads the servlet class and create instance of the servlet class (LoginServlet).
LoginServlet login = new LoginServlet();

Step 2. Then servlet container create ServletConfig object for that servlet and
Call login.init(ServletConfig);

Case 1 :
If you have overridden init(ServletConfig) method in your servlet then call goes to your
init(ServletConfig) method .

public void init(ServletConfig config) throws ServletException {
System.out.println("\n**** Initializing LoginServlet Init Servlet ********** \n");
super.init(config);
}
It will print "Initializing LoginServlet Init Servlet" and call goes to supper class GenericServlet init(ServletConfig) method.

In the GenericServlet init(ServletConfig) method there is code
This.config= config // initialize the Servlet config object and it is available to you.

Case 2 :
If you overridden init() method and not overridden init(ServletConfig) method.

Servlet container call login.init(ServletConfig);

There is no method like init(ServletConfig) in your servlet so call directly goes to super class GenericServlet init(ServletConfig) method.

This.config= config // initialize the Servlet config object and it is available to you.

You can get the Servlet config object using getServletConfig() method.


Conclusion: It is BETTER to use init(). If you use init() you have no such worries as calling super.init().
If you use init(servletconfig) and forgot to call super.init(config) then servletconfig object will not set and you will not get the servletconfig object.

More about this on http://techforum360.com/forum/viewthread?thread=31

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