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

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

  1. 1. Slide 1 of 30 Servlets And ServletContext
  2. 2. Slide 2 of 30 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
  3. 3. Slide 3 of 30 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.
  4. 4. Slide 4 of 30 Interface “ServletConfig”  To pass as an argument during initialisation.  The method – getServletName() – getInitParameter() – getServletContext()
  5. 5. Slide 5 of 30 Interface “ServletContext”  Retrieve and Send information about the server in which it is running.  Method of Servlet Context – getServerInfo() – getAttribute() – setAttribute()
  6. 6. Slide 6 of 30 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()
  7. 7. Slide 7 of 30 ServletContextEvent This is the event class for notifications about changes to the servlet context of a web application.  getServletContext()
  8. 8. Slide 8 of 30 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 implementation class must be configured in the deployment descriptor for the web application. • attributeAdded() • attributeRemoved() • attributeReplaced()
  9. 9. Slide 9 of 30 ServletContextAttributeEvent This is the event class for notifications about changes to the attributes of the servlet context of a web application. – getName() – getValue()
  10. 10. Slide 10 of 30 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.
  11. 11. Slide 11 of 30 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.
  12. 12. Slide 12 of 30 RequestDispatcher  include(ServletRequest request, ServletResponse response) Includes the content of a resource (servlet, JSP page, HTML file) in the response.
  13. 13. Slide 13 of 30 Error Handling in Servlet
  14. 14. Slide 14 of 30 Status Code
  15. 15. Slide 15 of 30 Reporting Error(HttpResponse)  sendError(): Sends an error response to the client using the specified status.  setStatus(): Sets the status code for this response.
  16. 16. Slide 16 of 30 Logging Errors  Servlet can store the actions and error throught the log() method of GenericServlet class
  17. 17. Slide 17 of 30 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 17
  18. 18. Slide 18 of 30 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 18
  19. 19. Slide 19 of 30 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”> 19
  20. 20. Slide 20 of 30 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> 20
  21. 21. Slide 21 of 30 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. 21
  22. 22. Slide 22 of 30 Cookie
  23. 23. Slide 23 of 30 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() 23
  24. 24. Slide 24 of 30 Working Cookie  Using HttpResponse  Using HttpRequest
  25. 25. Slide 25 of 30 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 25
  26. 26. Slide 26 of 30 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() 26
  27. 27. Slide 27 of 30 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()
  28. 28. Slide 28 of 30 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()
  29. 29. Slide 29 of 30 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()
  30. 30. Slide 30 of 30 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 implementation class must be configured in the deployment descriptor for the web application – sessionCreated() – sessionDestroyed()
  31. 31. Slide 31 of 30 HttpSessionListener
  32. 32. Slide 32 of 30 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()
  33. 33. Slide 33 of 30 HttpSessionEvent  This is the class representing event notifications for changes to sessions within a web application. – getSession()
  34. 34. Slide 34 of 30 Summary 34

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