servlets interview questions

5)What is session?

The session is an object used by a servlet to track a user's interaction with a Web application across multiple HTTP requests. The session is stored on the server.

6)What is servlet mapping?

 The servlet mapping defines an association between a URL pattern and a servlet. The mapping is used to map requests to Servlets.

7)What is servlet context

The servlet context is an object that contains a information about the Web application and container.  Using the context, a servlet can log events, obtain URL references to resources, and set and store attributes that other servlets in the context can use.

8)What is a servlet?

servlet is a java program that runs inside a web container.

9)Can we use the constructor, instead of init(), to initialize servlet?

Yes. But you will not get the servlet specific things from constructor. The original reason for init() was that ancient versions of Java couldn’t dynamically invoke constructors with arguments, so there was no way to give the constructor a ServletConfig. That no longer applies, but servlet containers still will only call your no-arg constructor. So you won’t have access to a ServletConfig or ServletContext.

10)How many JSP scripting elements are there and what are they?

 There are three scripting language elements: declarations, scriptlets, expressions.

11)How can I implement a thread-safe JSP page?

You can make your JSPs thread-safe adding the directive <%@ page isThreadSafe="false" % > within your JSP page.

12)What is the difference in using request.getRequestDispatcher() and context.getRequestDispatcher()?

In request.getRequestDispatcher(path) in order to create it we need to give the relative path of the resource. But in   resourcecontext.getRequestDispatcher(path) in order to create it we need to give the absolute path of the resource.

13)What are the lifecycle of JSP?

When presented with JSP page the JSP engine does the following 7 phases.

 Page translation: -page is parsed, and a java file which is a servlet is created.

Page compilation: page is compiled into a class file

Page loading : This class file is loaded.

Create an instance :- Instance of servlet is created

jspInit() method is called

_jspService is called to handle service calls

_jspDestroy is called to destroy it when the servlet is not required.

14)What are context initialization parameters?

Context initialization parameters are specified by the <context-param> in the web.xml file, these are initialization parameter for the whole application.

15)What is a Expression?

Expressions are act as place holders for language expression, expression is evaluated each time the page is accessed. This will be included in the service method of the generated servlet

16)What is a Declaration?

 It declares one or more variables or methods for use later in the JSP source file. A declaration must contain at least one complete declarative statement. You can declare any number of variables or methods within one declaration tag, as long as semicolons separate them. The declaration must be valid in the scripting language used in the JSP file. This will be included in the declaration section of the generated servlet.

17)How do I include static files within a JSP page?

 Static resources should always be included using the JSP include directive. This way, the inclusion is performed just once during the translation phase.