1. Vakgroep Informatietechnologie – Onderzoeksgroep (naam) Web Centric Design of Distributed Software

2. Objectives After this lab session you should be able to Write dynamic web applications Using the following technologies: Servlets, JSP and AJAX Server side plug-ins (Servlets) Separate thread per request Shares resources with other servlets Java Server Pages Plain HTML used for static information Java-scriptlets to code the dynamic parts Jsp-file is compiled in single Servlet ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 2

3. Objectives Asynchronous Javascript and XML (AJAX) Javascript technology to retrieve data from the server in the background No page refreshes ODS – Introduction to CORBA & RMI Vakgroep Informatietechnologie p. 3

4. Online Address Book ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 4

5. Outline 1.Database 2.Database Access 3.Authentication 4.Showing the contacts 5.Viewing/adding/deleting contacts ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 5

6. 1. Database ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 6

7. 1. Database ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 7

8. Outline 1.Database 2.Database Access 3.Authentication 4.Showing the contacts 5.Viewing/adding/deleting contacts ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 8

9. 2. Database Access Class to access the database Loads the correct driver Contains the connection url ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 9 // Driver for the Derby database String driver = "org.apache.derby.jdbc.ClientDriver"; // Connection settings String dbName = "contacts"; String user = "nbuser"; String password = "nbuser"; String connectionURL = "jdbc:derby://localhost:1527/" + dbName; public DatabaseAccess() { try { Class.forName(driver); } catch(java.lang.ClassNotFoundException e) { … }

10. 2. Database Access Data retrieval ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 10 public ResultSet executeQuery(String query) { ResultSet results; try { // connect to the database Connection conn = DriverManager.getConnection(connectionURL, user, password); s = conn.createStatement(); results = s.executeQuery(query); return results; } catch (Exception e) { e.printStackTrace(); return null; }

11. 2. Database Access Data update ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 11 public void executeUpdate(String query) { try { // connect to the database Connection conn = DriverManager.getConnection(connectionURL, user, password); s = conn.createStatement(); s.executeUpdate(query); } catch (Exception e) { e.printStackTrace(); }

12. Outline 1.Database 2.Database Access 3.Authentication 4.Showing the contacts 5.Viewing/adding/deleting contacts ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 12

13. 3. Authentication Login form in index.jsp ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 13 /LoginServlet"> User name: Password: Using the syntax we can generate dynamic output in a JSP

14. 3. Authentication Login Servlet ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 14 protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // Get the username and password from the request String user = request.getParameter("username"); String pass = request.getParameter("password"); //Create the database object DatabaseAccess dbAccess = new DatabaseAccess(); ResultSet users; … } With request.getParameter() the encoded parameters of the form can be retrieved

15. 3. Authentication Login Servlet ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 15 // Get all users from the database users = dbAccess.executeQuery("select * from USERS"); try { while (users.next()) { String username = users.getString("username"); String password = users.getString("password"); if (username.equals(user) && password.equals(pass)) { // A match is found, access is allowed allowed = true; break; } // Close the resultSet users.close(); } catch (Exception e) { e.printStackTrace(); }

16. 3. Authentication Login Servlet ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 16 if (allowed) { // Add the username and database object to the session object HttpSession session = request.getSession(true); session.setAttribute("dbAccess", dbAccess); session.setAttribute("username", user); // Forward to the ContactsServlet RequestDispatcher dispatcher = request.getRequestDispatcher("ContactsServlet"); dispatcher.forward(request, response); } - The HttpSession object is used to bind a client to a servlet over multiple requests (session tracking) - The RequestDispatcher object is used to forward requests to other resources or to include the contents of another servlet to the response of this servlet

17. 3. Authentication Login Servlet ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 17 else { response.setContentType("text/html;charset=UTF-8"); PrintWriter out = response.getWriter(); out.println(" "); out.println(" LoginServlet "); out.println(" "); out.println("You failed to supply valid credentials."); out.println(" "); out.close(); }

18. Outline 1.Database 2.Database Access 3.Authentication 4.Showing the contacts 5.Viewing/adding/deleting contacts ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 18

19. 4. Showing the contacts We need to check if the user has logged in properly User could go directly to url of ContactsServlet Check is needed throughout whole application Implemented in separated servlet ( CheckCredentialsServlet ) Included in other servlets via RequestDispatcher object ContactsServlet: ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 19 … // Check if the user is logged in RequestDispatcher dispatcher = request.getRequestDispatcher("CheckCredentialsServlet"); dispatcher.include(request, response); …

20. 4. Showing the contacts CheckCredentialsServlet ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 20 PrintWriter out = response.getWriter(); // Get the username from the session HttpSession session = request.getSession(); String username = (String) session.getAttribute("username"); if (username == null) { // The user is not logged in out.println(" "); out.println(" CheckCredentialsServlet "); out.println(" "); out.println("You are not logged in. Click here to login."); out.println(" "); // close the output out.close(); }

21. 4. Showing the contacts ContactsServlet: ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 21 … // Get the username and database object from the session HttpSession session = request.getSession(); String username = (String) session.getAttribute("username"); DatabaseAccess databaseAccess = (DatabaseAccess) session.getAttribute("dbAccess"); … // Get all the contacts of the user String query = "select \"CONTACTNAME\" from USERCONTACTS where \"USERNAME\" = '" + username + "'"; ResultSet results = databaseAccess.executeQuery(query); try { while (results.next()) { String contactname = results.getString("contactname"); out.println(" " + contactname + " View Remove "); } …

22. Outline 1.Database 2.Database Access 3.Authentication 4.Showing the contacts 5.Viewing/adding/deleting contacts ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 22

23. 5. Viewing/adding/deleting contacts 3 extra servlets All information they need is sent via the urls or via the request body Each servlet includes CheckCredentialsServlet AddContactServlet: ODS – Introduction to Web Centric technologies Vakgroep Informatietechnologie p. 23 … // Update the CONTACTS table String query = "insert into CONTACTS Values('" + contactname + "','" + telephone + "','" + address + "')"; databaseAccess.executeUpdate(query); // Update the USERCONTACTS table String query2 = "insert into USERCONTACTS Values('" + username + "','" + contactname + "')"; databaseAccess.executeUpdate(query2); // Go back to ContactsServlet response.sendRedirect("ContactsServlet");