Session 2 servlet context and session tracking - Giáo trình Bách Khoa Aptech

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Servlets And ServletContext

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Objectives
 Initialising Servlets
 ServletContext
 RequestDispatcher
 Error Handling in Servlets
 Introduction to Session Tracking
 Session Tracking Techniques
 Session Tracking Using Cookies
 Session Tracking Using HttpSession
 Session Event Handling

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Need for Initialising Servlets
In Web Application, the database connection
information, such as SQL user name and
password are not send to the servlet every time
a client makes a request. Hence, this
information need to be passed tho the servlet
before beginning the servlet life cycle. To pass
the parameter from the client side to the
servlets for executing the first time and retrieve
the data required as specified by the user the
servlet needs to be initialised.

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Interface “ServletConfig”
 To pass as an argument during initialisation.
 The method
– getServletName()
– getInitParameter()
– getServletContext()

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Interface “ServletContext”
 Retrieve and Send information about the server
in which it is running.
 Method of Servlet Context
– getServerInfo()
– getAttribute()
– setAttribute()

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Interface “ServletContextListener”
Implementations of this interface receive
notifications about changes to the servlet
context of the web application they are part of.
To recieve notification events, the
implementation class must be configured in the
deployment descriptor for the web application.
• contextInitialized()
• contextDestroyed()

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ServletContextEvent
This is the event class for notifications about
changes to the servlet context of a web
application.
 getServletContext()

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ServletContextAttributeListener
Implementations of this interface recieve notifications of
changes to the attribute list on the servlet context of a web
application. To recieve notification events, the
deployment descriptor for the web application.
• attributeAdded()
• attributeRemoved()
• attributeReplaced()

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ServletContextAttributeEvent
This is the event class for notifications about
changes to the attributes of the servlet context
of a web application.
– getName()
– getValue()

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RequestDispatcher
 Defines an object that receives requests from the client
and sends them to any resource (such as a servlet, HTML
file, or JSP file) on the server. The servlet container creates
the RequestDispatcher object, which is used as a wrapper
around a server resource located at a particular path or
given by a particular name.
 This interface is intended to wrap servlets, but a servlet
container can create RequestDispatcher objects to wrap
any type of resource.

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RequestDispatcher
 Void forward(ServletRequest request, ServletResponse response)
Forwards a request from a servlet to another resource (servlet,
JSP file, or HTML file) on the server.

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RequestDispatcher
 include(ServletRequest request, ServletResponse response)
Includes the content of a resource (servlet, JSP page, HTML file) in the
response.

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Error Handling in Servlet

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Reporting Error(HttpResponse)
 sendError(): Sends an error response to the
client using the specified status.
 setStatus(): Sets the status code for this
response.

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Logging Errors
 Servlet can store the actions and error throught
the log() method of GenericServlet class

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Session
 Is the period of connection between client and server
 Is a group of activities that are performed by a user
while accessing a particular web site
 HTTP is a Stateless protocol
 Http Session are virtual connection between client and
server
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Session Tracking
 Allows the server to keep a track of successive requests
made by same client
 Session Tracking Techniques
– Hidden form field
– URL rewriting
– Cookies
– HttpSession interface
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Hidden Form Field
 Simplest technique to maintain the state of an end
user.
 Embedded in an HTML form.
 Not visible when you view an HTML file in a browser
window.
– <input type=“hidden” name=“productId” value=“P01”>
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URL Rewriting
 Maintains the state of end user by modifying the URL.
 Adds some extra data at the end of the URL
 Is used when the information to be transferred is not
critical.
– <a href=“http://localhost:8080/Books?category=java”> Java
Books </a>
– <form action=“http://localhost:8080//UpdateProfile?
uid=123” method=“get”> ---------- </form>
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Cookie
 Is a small piece of information sent by the web
server to the client to keep track of users.
 Cookie has values in the form of key-value pairs
 Types of Cookie
– Temporary Cookie
– Persistent Cookie
 A web browser is expected to support 20 Cookies
per host
 Size of each cookie can be a maximum of 4 KB.
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Cookie
– Cookie cookie1 = new Cookie(“CustId”,”123”);
– public void addCookie(cookie1);
– Cookie [] cookies = request.getCookies();
– public String getValue();
– public void setValue(String newValue)
– public String getName()
– public void setMaxAge(int expiry)
– public int getMaxAge()
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Working Cookie
 Using HttpResponse
 Using HttpRequest

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HttpSession
– Provides a way to identify a user across more than
one page request or visit to a Web site and to store
information about that user
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HttpSession
– request.getSession(boolean create)
– public String getId()
– public Object getAttribute(String name)
– public void setAttribute(String name, Object value)
– public void removeAttribute(String name)
– public long getCreationTime()
– public long getLastAccessedTime()
– public int getMaxInactiveInterval()
– public void setMaxInactiveInterval(int interval)
– public boolean isNew()
– public void invalidate()
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HttpSessionAttributeListener
This listener interface can be implemented in order to get
notifications of changes to the attribute lists of sessions
within this web application.
– attributeAdded()
– attributeRemoved()
– attributeReplaced()

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HttpSessionBindingListener
Causes an object to be notified when it is bound to or
unbound from a session. The object is notified by an
HttpSessionBindingEvent object.
– valuedBound()
– valueUnbound()

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HttpSessionBindingEvent
Events of this type are either sent to an object that
implements HttpSessionBindingListener when it is
bound or unbound from a session, or to a
HttpSessionAttributeListener that has been configured
in the deployment descriptor when any attribute is
bound, unbound or replaced in a session.
– getName()
– getSession()
– getValue()

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HttpSessionListener
Implementations of this interface may are notified of
changes to the list of active sessions in a web
application. To recieve notification events, the
deployment descriptor for the web application
– sessionCreated()
– sessionDestroyed()

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HttpSessionListener

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HtppSessionActivationListener
Objects that are bound to a session may listen to
container events notifying them that sessions
will be passivated and that session will be
activated.
– sessionDidActive()
– sessionWillPassivate()

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HttpSessionEvent
 This is the class representing event notifications
for changes to sessions within a web
application.
– getSession()

Session 2 servlet context and session tracking - Giáo trình Bách Khoa Aptech

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