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| What is the
servlet? |
Servlet is
a script, which resides and executes on server side, to create dynamic
HTML. In servlet programming we will use java language. A servlet can
handle multiple requests concurrently
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| What
is the architechture of
servlet package? |
Servlet Interface is the
central abstraction. All servlets implements this Servlet
Interface either direclty or indirectly
( may implement or extend Servlet Interfaces sub classes or sub
interfaces)
Servlet
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Generic Servlet
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HttpServlet ( Class ) -- we will extend this class to handle GET / PUT
HTTP requests
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MyServlet
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| What
is the difference between
HttpServlet and GenericServlet? |
A
GenericServlet has a service() method to handle requests.
HttpServlet extends GenericServlet added new methods
doGet()
doPost()
doHead()
doPut()
doOptions()
doDelete()
doTrace() methods
Both these classes are abstract.
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| What's
the difference between
servlets and applets? |
Servlets
executes on Servers. Applets executes on browser. Unlike applets,
however, servlets have no graphical user interface.
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| What
are the uses of Servlets? |
A servlet
can handle multiple requests
concurrently, and can synchronize requests. Servlets can forward
requests to other servers and servlets. Thus servlets can be used to
balance load among several servers.
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| When
doGET() method will going
to execute? |
When we
specified method='GET' in HTML
Example : < form name='SSS' method='GET'>
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| When
doPOST() method will going
to execute? |
When we
specified method='POST' in HTML
< form name='SSS' method='POST' >
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| What
is the difference between
Difference between doGet() and doPost()? |
GET Method
: Using get method we can able to pass 2K data from HTML
All data we are passing to Server will be displayed in URL (request
string).
POST Method : In this method we does not have any size limitation.
All data passed to server will be hidden, User cannot able to see this
info
on the browser.
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What
is the servlet life cycle?
|
When first
request came in for the servlet , Server will invoke init() method of
the servlet. There after if any user request the servlet program,
Server will directly executes the service() method.
When Server want to remove the servlet from pool, then it will execute
the destroy() method
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Which
code line must be set
before any of the lines that use the PrintWriter?
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setContentType()
method must be set.
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Which
protocol will be used by
browser and servlet to communicate ?
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HTTP
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In
how many ways we can track
the sessions?
|
Method 1)
By URL rewriting
Method 2) Using Session object
Getting Session form HttpServletRequest object
HttpSession session =
request.getSession(true);
Get a Value from the session
session.getValue(session.getId());
Adding values to session
cart = new Cart();
session.putValue(session.getId(), cart);
At the end of the session, we can inactivate the session by using the
following command
session.invalidate();
Method 3) Using cookies
Method 4) Using hidden fields
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How
Can You invoke other web
resources (or other servlet / jsp ) ?
|
Servelt can
invoke other Web resources in two ways: indirect and direct.
Indirect Way : Servlet will return the resultant HTML to the browser
which will point to another Servlet (Web resource)
Direct Way : We can call another Web resource (Servelt / Jsp) from
Servelt program itself, by using RequestDispatcher object.
You can get this object using getRequestDispatcher("URL") method. You
can get this object from either a request or a Context.
Example :
RequestDispatcher dispatcher =
request.getRequestDispatcher("/jspsample.jsp");
if (dispatcher != null)
dispatcher.forward(request, response);
}
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How
Can you include other
Resources in the Response?
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Using
include method of a RequestDispatcher object.
Included WebComponent (Servlet / Jsp) cannot set headers or call any
method (for example, setCookie) that affects the headers of the
response.
Example : RequestDispatcher dispatcher =
getServletContext().getRequestDispatcher("/banner");
if
(dispatcher != null)
dispatcher.include(request,
response);
}
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What
is the difference between
the getRequestDispatcher(String path) ServletRequest interface and
ServletContext interface?
|
The
getRequestDispatcher(String path) method of ServletRequest
interface accepts parameter the path to the resource to be included or
forwarded to, which can be relative to the request of the calling
servlet. If the path begins with a "/" it is interpreted as relative to
the current context root.
The getRequestDispatcher(String path) method of ServletContext
interface cannot accepts relative paths. All path must sart with a "/"
and are interpreted as relative to curent context root. If the resource
is not available, or if the server has not implemented a
RequestDispatcher object for that type of resource,
getRequestDispatcher will return null. Your servlet should be prepared
to deal with this condition.
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What
is the use of
ServletContext ?
|
Using
ServletContext, We can access data from its
environment. Servlet context is common to all Servlets so all Servlets
share the information through ServeltContext.
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Is
there any way to generate
PDF'S dynamically in servlets?
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We need to
use iText. A open source library for java. Please refer sourceforge
site for sample servlet examples.
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What
is the difference between
using getSession(true) and getSession(false) methods?
|
getSession(true)
- This method will check whether
already a session is existing for the user. If a session is existing,
it will return that session object, Otherwise it will create new
session object and return taht object.
getSession(false) - This method will
check
existence of session. If session exists, then it returns the reference
of that session object, if not, this methods will return null.
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