1.Explain JSP life Cycle methods?

• jsp engine controls the life cycle of jsp
• Jsp life cycle is described by three life cycle methods and six life cycle phases

Jsp life cycle methods :

• jspInit()
• _jspService()
• jspDestroy()

• Jspinit() method is invoked when JSP page is initialized.
• The _jspService() method corresponds to the body of the jsp page.
• This method is defined automatically by the JSp container and should never be defined y the JSP page author.

Jsp Life cycle Phases: 

• Translation phase
• Compilation phase
• Instantiation phase
• initialization phase
• Servicing phase
• Destruction phase

Read More at : JSP Life Cycle

2. What are the Jsp Implicit Objects?

• Implicit objects in jsp are the objects that are created by the container automatically and the container makes all these 9 implicit objects to the developer.
• We do not need to create them explicitly, since these objects are created and automatically by container and are accessed using standard variables(objects) are called implicit objects.
• The following are of implicit variables available in the JSP.  

1. out
2. request
3. response
4. config
5. application
6. session
7. pagecontext
8. page
9. exception

Read More at: 9 Jsp Impicit Objects in java

3. Explain Jsp Scripting Elements?

• Jsp scripting elements are used to embed jva code in to the jsp.
• Jsp scripting elements are three types
  
  1. Declaration
  2. Expression
  3. Scriplet

Read More at: Jsp Scripting Elements

4. What are the Directives in Jsp?

• A jsp directive is a translation time instruction to the jsp engine.
• we have three kinds of directives.

1. Page directive
2. Include directive
3. Taglib directive

 Read More at: Jsp Directive Elements

 5. What are the differences between include directive and include action?

 

6. How to disable session in JSP?

• By using page directive
• <%@ page session="false" %> 

7. How can we handle exceptions in a JSP page?

• We can handle exception in jsp by using error page element of page directive 

• The errorPage attribute tells the JSP engine which page to display if there is an error while the current page runs.
  The value of the errorPage attribute is a relative URL.
  The following directive displays MyErrorPage.jsp when all uncaught exceptions are thrown
  

  Syntax:

  errorPage="url"
  

  Example:

  <%@ page errorPage="error.jsp"%>

8.How can we override jspInit() and jspDestroy() methods in a jsp?

• Both methods are executed once in a life cycle of a jsp.
• We can override these two method as shown below.
• <%!
      public void jspInit() {
          . . .
      }
  %>
• <%!    
      public void jspDestroy() {
          . . .   
      }
  %>

9.Can a JSP extend a java class?

• Yes we can extend a java class in jsp
• <%@ include page extends="classname" %>
• We can do this because jsp will convert to a servlet so a servlet can extend a class its fine

1.Explain Servlet life cycle in java.

• Servlet engine controls the life cycle of servlet
• Servlet life cycle is described by three life cycle methods under 5 life cycle phases
• life cycle methods are

1. init(ServletConfig obj)
2. service(servletRequest, servletResponse)
3. destroy() 

• When ever somethings happens in the life of servlet. servlet engine calls these methods on the servlet instance and hence the name.

2.What is ServletConfig ?

• Request parameters are used by the servlet to receive data from client to process the request.
• Some specific data must be supplied to the servlet at the time of initialization of the servlet and this data is specific to the client.But data is not supplied by the client via request parameters
• Use initialization parameters to supply the data to the servlet at the time of initialization of the servlet. initialization parameters are set in deployment descriptor   (Web.xml).
• Servlet can access these parameters during the run time
• Request parameters change form Request to request 
• Initialization parameters change from servlet to servlet.

3. What is ServletContext?

• We can deploy multiple web applications in a servlet container.
• Each web application contains its own resources in a separate  environment. This environment called ad Web Application context or ServletContext.
• The resources belongs to the one web application context are not available to the other web application context.
• A Servlet context contains zero or more number of servlets. For every servlet object the container creates separate ServletConfig object.

4. Can we define a Constructor in servlet?

• Yes we can define a constructor in servlet but we can not call the constructor explicitly because servlet container will create the object of servlet so it will be called by the servlet container.

5. Can we call destroy() method inside init() method of a servlet. If yes what will happen?

• Yes we can call destroy() method inside a init() method.
• Actually container will call destroy() method if we call that method explicitly nothing will happen.
• If we override destroy() method and called from init(). method will be called and code will be executed.

6.What are the difference between GenericServlet and HttpServlet?

7.What are the differences between doGet() and doPost()?

8. Can we call a servlet from another servlet?

• Yes. We can call a servlet from another servlet this is known as inter servlet communication.
• By using RequestDispatcher object we can do this.
• RequestDispatcher rd=request.getRequestDispatcher("other servlet url name");
• rd.forward(req, res);

9. What are the differences between forward() and sendRedirect() methods?

10.How can you get the information about one servlet context in another servlet?

• By using setAttribut() method we can set the data in one servlet and get in another
• Context.setAttribute (“name”,” value”)
• Context.getAttribute (“name”)

11.Explain Servlet architecture?

• Frequently asking java interview question in servlets you may get questions like
• explain the architecture of java servlet?
• explain the architecture of java servlet with diagram?
• define the servlet architecture?
• servlet architecture overview?
• Servlets read the explicit data sent by the clients (browsers). This includes an HTML form on a Web page or it could also come from an applet or a custom HTTP client program.
• Read the implicit HTTP request data sent by the clients (browsers). This includes cookies, media types and compression schemes the browser understands, and so forth.

• Implicit objects in jsp are the objects that are created by the container automatically and the container makes all these 9 implicit objects to the developer.
• We do not need to create them explicitly, since these objects are created and automatically by container and are accessed using standard variables(objects) are called implicit objects.
• The following are of implicit variables available in the JSP.  

1.out:

•  out is one the implicit object to write the data to the buffer and send output to the client in response.
• out object allows us to access the servlets output stream and has a pagescope.
• out.print("");
• out is the object of javax.servlet.jsp.JspWriter class.
• While working with servlet we need printWriter object
• PrintWriter out=response.getWriter();   
• In servlet we are used PrintWriter to send the output to the client. In JSP we use JSPWriter. 
  

Difference between JspWriter and PrintWriter:

• Every JSPWriter is associated with 8KB of internal Buffer. Where as PrintWriter doesn’t associated with any Buffer.
• The methods of the JspWriter class are designed to throw java.io.IOException where as the methods of PrintWriter class are not throw Exception.
• JspWriter is an abstract class present in javax.servlet package.
• PrintWriter is a class defined in java.io package.

JspWriter out object in jsp:

Printwriter object in servlet:

2.request:

• request implicit object is the object of  type  HttpServletRequest.
• request object will be created by the container for every request.
• It will be used to get request information like parameter , header information ,server name server port etc.
• By using request object we can able to set ,get and remove attributes from request scope.
• It uses the getPareameter() method to access request parameter.
• The container passes this object to the _jspService() method.

3.response:

• response is an instance of class which implements the HttpServletResponse interface.
• Container generates this object and passes to the _jspService() method as parameter.
• response object will be created by the container for each request.
• It represents the response that to be given to the client. 
• The response implicit object is  used to content type, add cookie and redirect the response to another resource.

1.set content type.

2.Redirect response:

3. To send the error message directly to the client:

4.config

• config is one of the implicit object of type javax.servlet.ServletConfig.
• config object is created by the web container for each jsp page.
• config object used to get initialization parameters from web.xml file.

• servletConfig is an object used by servlet container to pass the information during initialization.
• Once if we get the ServletConfig object, we can find the name of the servlet which is configured in web.xml file by using a method getServletName() method.

5.application:

• application is one of the implicit object of type javax.servlet.ServletContext.
• application object is created by the web container one per application when the application gets deployed.
• application object used to get context parameters from web.xml file.
• ServletContext object contains set of methods which are used to interact with ServletContainer. By using these methods we can find the information about ServletContainer.
• When ever sun micro system releases a new version of API. It is the responsibility of server vender to provide the implementation to the latest API. 
• For example when servlet 2.5 is released Tomcat guys has provided the implementation and integrated it in Tomcat 6.0 the latest version of servlet API is 3.0 this version is integrated in Tomcat 7.0.
   

6.session

• session implicit object is holding HttpSession object.
• session object used to set, get, and remove attributes to the session scope and also used to get session information.

index.html

welcome.jsp

showuserinfo.jsp

7.pagecontext:

• pagecontext implicit object is type of  PageContext.
• pagecontext object used to set , get and remove attributes in particular scope

1. page scope
2. request scope
3. session scope
4. application scope

8.page

• Page implicit variable hold the currently executes Servlet object for the corresponding JSP.
• Acts as this object for current jsp page

9.exception

• The implicit variable can be used only in Error pages. When we try to use this variable in a JSP which is not an Error page we get an Error message.

Page Directive:

• Page directive is one of the three translation time instructions to the jsp engine.
• Page directive has 13 attributes.
• Mostly page directive used to import java packages in to jsps
  <% @ page import="java.sql.*, java.util,*"%>

Jsp Page directive attributes:

1. import
2. session
3. isErrorPage
4. errorPage
5. ContentType
6. isThreadSafe
7. extends
8. info
9. language
10. autoflush
11. buffer

import:

Syntax:

Example: