1. What is the different between web server and application server?
Web server
|
Application server
|
Web server provides environment to run Web
Applications
|
Application server provides environment to
run Enterprise Applications
|
Web server supports only for web related
Technologies like Servlet, Jsp, HTML etc.
|
Application server supports for any
technology from java like Servlet, jsp, EJB, and Jms components etc.
|
Example: Tomcat, Oracle HTTP Server
|
Example: Weblogic, WebSphere, Jboss
|
Application server provides additional
features along with WebServer
|
2. What is the different between Web Application and Enterprise Application?
Web
Application:
3. What is the difference between GET and POST method?
GET
|
POST
|
We can send limited amount
of data because data is send in header.
|
We can send large amount
of data because data is send in body.
|
GET method is not secure
because data is exposed in the URL bar
|
POST method is secure
because data is not exposed in the URL bar
|
we can easily bookmark it
|
We can’t bookmark it
|
GET is the default HTTP
method
|
WE can specify the POST method
|
It is more efficient and idempotent
|
It is less efficient and
non- idempotent
|
4. What is web application directory structure?
5. What is a Servlet?
Servlet is
server side technology
is used to create web application, Servlet is an interface that must be
implemented for creating any servlet.
Servlet is an
API that provides many interfaces and classes.
public
abstract class GenericServlet implements
Servlet, ServletConfig,
Serializable public abstract class HttpServlet extends GenericServlet
6. What is the difference between GenericServlet and HttpServlet?
GenericServlet
|
HttpServlet
|
GenericServlet is protocol
independent implementation of Servlet interface
|
HttpServlet is HTTP
protocol specific implementation
|
javax.servlet.GenericServlet;
|
javax.servlet.http.HttpServlet;
|
GenericServlet
implements Servlet
|
HttpServlet
extends GenericServlet
|
It is contain ServletRequest ,ServletResponse
intefaces
|
It contain HttpServletRequest ,HttpServletResponse
interfaces
|
7. What is the Servlet life cycle?
A servlet life cycle can be defined as the entire process from its creation till the destruction. The following are the paths followed by a servlet.
init() method is used initialize the servelt. It is called only once when the servlet is first created.
service() method is used process the client request. Each time service() method is called for every client request, create one thread for one request.
destroy() method is used to terminate the servlet. destroy() method is called only once at the end of the life cycle of a servlet.
8. What is the difference between PrintWriter and
ServletOutputStream?
PrintWriter
|
ServletOutputStream
|
PrintWriter
is a character-stream class
|
ServletOutputStream
is a byte-stream class
|
The
PrintWriter class can be used to write only character-based information
|
ServletOutputStream
class can be used to write primitive values as well as character-based
information
|
PrintWriter out =response.getWriter();
out.println(“Hello”);
|
ServletOutputStream
out = response.getOutputStream();
|
9. What is the purpose of RequestDispatcher Interface?
The RequestDispacher interface provides the facility of
dispatching the request to another resource it may be html, jsp or another servlet in same application. We can also include the content of
another resource to the response.
10. How do we call one Servlet from
another Servlet?
We
can use RequestDispatcher forward() method to forward the processing of a
request to another servlet. If we want to include the another servlet output to
the response, we can use RequestDispatcher include() method.
11. What are the major tasks
of Servlet Container?
Multithreading
Support:
Container creates new thread for every request to the servlet and provides them
request and response objects to process.
JSP Support: JSPs doesn’t look
like normal java classes but every JSP in the application is compiled by
container and converted to Servlet and then container manages them like other
servlets.
Lifecycle and
Resource Management: Servlet Container takes care of managing the life cycle of
servlet. From the loading of servlets into memory, initializing servlets,
invoking servlet methods and to destroy them.
Communication
Support: Servlet
Container provides easy way of communication between web client (Browsers) and
the servlets and JSPs. Because of container, we don’t need to build a server
socket to listen for any request from web client, parse the request and
generate response. All these important and complex tasks are done by
container and all we need to focus is on business logic for the applications.
12. What are the advantages of Servlet
over CGI?
Servlet
|
CGI (Common Gateway Interface)
|
Servlets can run on any
operating system because Servlets are platform-independent
|
We need to recompile the
programs in the new operating system
|
Performance is
significantly better
|
Performance
is not good
|
Servlets share the memory
space of the JVM
|
CGI create their own
process when they are executed
|
Servlets run on the JVM
|
CGI programs run as
separate processes
|
The full functionality of the Java class
libraries is available to a servlet. It can communicate with applets,
databases, or other software via the sockets and RMI mechanisms
|
13. What is doGet() and
doPost() methods?
doGet() method:
A GET request results from a
normal request for a URL or from an HTML form that has no METHOD specified and
it should be handled by doGet() method.
This method should be used
to get data from server.
doPost() method:
A POST request results from
an HTML form that specifically lists POST as the METHOD and it should be handled
by doPost() method.
This method should be used
to get data from server.
14. What is difference between
ServletConfig and ServletContext?
ServletConfig
|
ServletContext
|
ServletConfig is a unique
object per servlet
|
ServletContext is a unique
object for complete application
|
ServletConfig is used to
provide init parameters to the servlet
|
ServletContext is used to
provide application level init parameters that all other servlets can use
|
We can’t set attributes in
ServletConfig object
|
we can set attributes in
ServletContext that other servlets can use in their implementation
|
javax.servlet.ServletConfig;
|
javax.servlet.ServletContext;
|
15. What are the Cookies?
Cookies are text files stored on the client computer and they are kept
for various information tracking purpose. Java Servlets transparently supports
HTTP cookies. Cookie works at client side.
Create Cookie Cookie ck=new Cookie(“key”, “value”); To read Cookie we call getCookies( ) method of HttpServletRequest.
Create Cookie Cookie ck=new Cookie(“key”, “value”); To read Cookie we call getCookies( ) method of HttpServletRequest.
16. What is the session?
Session
provides a way to identify a user across more than one page request. The
session persists for a specified time period, across more than one connection
or page request from the user. Session is work at server side.
Create session
HttpSession session=request.getSession();
session.setAttribute("name",n);
17. What
are the HttpServletRequest and HttpServletResponse?
HttpServletRequest:
When a browser sends
requests for a web page, HttpServletRequest is to receive data sent by client
HttpServletResponse:
When a Web server responds
to the client request, HttpServletResponse is to send the response data to the client.
18. Can we call a jsp file from the servlet?
Yes, we can call a jsp file from the Servlet by using
RequestDispatcher interface
RequestDispatcher rd=request.getRequestDispatcher("home.jsp");
rd.forward(request,response);
19. How to read form data in
Servlet?
getParameter(): we call
request.getParameter() method to get the value of a form parameter.
getParameterValues(): Call this method
if the parameter appears more than once and returns multiple values, for
example checkbox.
getParameterNames(): Call this method
if you want a complete list of all parameters in the current request.
20. What are the attribute in Servlets and uses?
Attribute are set, get or remove and their scope request,
session or application scope. Servlet
attributes are used to communicate one servlet to other servlet.
21. What are the annotations used in Servlet?
There are mainly 3 annotations we use in servlet.
@WebServlet : use for servlet class.
@WebListener : use for listener class.
@WebFilter : use for filter class.
22. When servlet object is created and who is responsible to
create the servlet object?
Servlet object create at the time of first request and
web container or servlet container is responsible to create servlet object.
23. Difference between forward() method and sendRedirect()
method ?
forward()
|
sendRedirect()
|
forward()
sends the same request to another resource.
|
sendRedirect()
method sends new request always because it uses the URL bar of the browser.
|
forward()
method works at server side
|
sendRedirect()
method works client side
|
forward() is handled
internally by the container
|
sednRedirect() is handled
by browser
|
24. What
is the filter? And types of filters in servlet?
Filter is
an object that is invoked and it is pluggable java components the we can use to preprocessing or post processing of the request.
Various types of filters:
Authentication
Filters. Data compression Filters. Encryption Filters. Filters that trigger resource access events. Image Conversion Filters. Logging and Auditing Filters.