Transcript Web Design & Development

Servlets 4
Lec 30
Web Design and Development
Looking Back…


Response Redirection
 Sending
a standard redirect
 Sending
a redirect to an error page
Request Dispatching
 Forward
 Include
Include Diagram
Example Code
Request Dispatching: include
Forward Diagram
Example Code
Request Dispatching: forward
HTTPServletRequest
methods
More HttpServletRequest
methods

setAttribute (String, Object) /
getAttribute(String)
 Stores an attribute in this request as key-value
pair form
 Attributes are set/reset between requests
 Often used in conjunction with
RequestDispatcher
More HttpServletRequest
methods cont.

getMethod()
 Returns

the name of HTTP method (get & post etc)
getRequestURL()
 Returns
the part of this request’s URL
 Query string is not included

getProtocol()
 Returns
the name & version of the protocol used
More HttpServletRequest
methods cont.

getHeaderNames()
 Returns
an enumeration of all the header names this
request contains

getHeader(String headername)
 Returns
the value of the specified request header as
String
 Returns null, if no header with the specified name
HTTPServletResponse
methods
More HttpServletResponse
methods

setContentType(String)
 Servlets almost always use this header
 MIME types

setContentLength(int)
 Sets the Content-Length header.

addCookie(Cookie)
 Adds a value to the Set-Cookie header.

sendRedirect (String)
 Redirect client to the specified URL
 Can accept relatives URL
Session Tracking
Session Tracking

HTTP is a stateless protocol
 Every
request is considered independent of every
other request

Many web applications need to maintain a
conversational state with the client
 A shopping
cart is a classic example
Continuity Problem
(User’s Point of View)
Server State
Page 1
Added book to
cart
Added book to
cart
Page 2
Page 3
Page 4
CC# = XXX
Billing address
Order submitted
& logged
Credit: Stanford’s java course
The illusion of Continuity
User thinks that choices made on page 1
are remembered on page 3
 However

 HTTP
is Stateless
 Requests from same user do not necessarily
come in adjacent requests
Continuity Problem
(Server’s Point of View)
Request 1
Request 2
Credit: Stanford’s java course