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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 !!!

Exception handling in Servlet and JSP specifications



In the previous section, you looked at the general principles in exception handling without a J2EE tilt. In this section, we will cover what servlet specification has to say about exception handling. Consider the doGet() method signature in a HttpServlet.

public void doGet(HttpServletRequest request,

HttpServletResponse response) throws

ServletException, IOException

The above method signature implies that a Servlet or a JSP (and finally a web application) is only allowed to throw

ServletException or its subclasses

IOException or its subclasses

RuntimeExceptions



All other checked exceptions have to be handled in the Servlet/JSP code in one of the following manner:

Catch the checked exception and log the error message and (or) take any business related action.

Wrap the exception in a ServletException and throw the ServletException. (ServletException has overloaded constructors to wrap the actual exception.)

Servlet specification provides exception-handling support through web.xml. In web.xml, you can declare <error-page> to handle exceptions that are thrown but not caught.



<error-page>

<exception-type>UnhandledException</exception-type>

<location>UnhandledException.jsp</location>

</error-page>



What this means is that if an exception of type UnhandledException is thrown from your web application but not caught anywhere, then the user gets to see the UnhandledException.jsp. This works well for ServletException, IOException, RuntimeException and their subclasses.

If the UnhandledException is a subclass of ServletException and none of the error-page declaration containing exception-type fit the class hierarchy of the thrown exception, then the Servlet container gets the wrapped exception using the ServletException.getRootCause method. Then the container attempts again to match the error-page declaration. This approach works well if the UnhandledException is not a subclass of ServletException or IOException (but is a checked exception). You have to throw a ServletException or its subclass by wrapping the UnhandledException in it and the servlet container does rest of the magic.

There are times when the user cannot see a page due to incorrect access rights or the page simply does not exist. The Servlet sends an error response with an appropriate HTTP error code. For instance, 404 corresponds to Page not found, 500 corresponds to Internal Server Error and so on. You can also assign JSPs for default HTTP error code as follows.



<error-page>

<error-code>404</error-code>

<location>exceptions/Page404.jsp</location>

</error-page>



Similarly, exceptions can occur in the JSPs in scriptlets and custom tags. These can throw runtime exceptions. In addition scriptlets can throw ServletException and IOException since a JSP gets translated into the body of _jspService() method and the signature of the _jspService() method is same as doGet().



public void _jspService(HttpServletRequest request,

HttpServletResponse response) throws

ServletException, IOException



Tags however throw JspException in their tag callback methods (doStartTag(), doEndTag() and so on). JspException is a direct subclass of java.lang.Exception and has no relationship with ServletException or IOException. The _jspService() method is container dependent but its contract is to catch all those exceptions and forward the request to the errorPage specified by the JSP. Hence it is a best practice to assign error pages in JSPs with the declarative: <%@ page errorPage="/error.jsp" %>

When forwarding to the exception page as specified by errorPage setting shown above, the exception describing the error is stored as request attribute with the key ?javax.servlet.jsp.JspException?. If the JSP assigned to handle the exceptions has the directive <%@ page isErrorPage="true" %> at the top of their page, then the exception is provided as the implicit scripting variable named exception.


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