Servlets e JSP

1. Servlets e JSP

2. Applets • Special Java programs (without a “main”) callable from HTML and executed in a graphic context. • They can be executed by: • a Java enabled Web Browser; • ad-hoc programs (e.g. Sun AppletViewer).

3. Applets • Every applet is implemented by creating a subclass of the Applet class. • The hierarchy determines much of what an applet can do and how.

4. Applet Lifecycle • An applet can react to major events in the following ways: • It can initialize itself. init() • It can start running. start() • It can draw some graphics. paint() • It can respond to user-generated events (Mouse, keyboard, menus…). handleEvent() • It can stop running. stop() • It can perform a final cleanup, in preparation for being unloaded. destroy()

5. Applet Lifecycle • Whenever it’s needed, • at lower priority init() Multithreading! start() handleEvent() paint() stop() Actually, more threads are active behind the scenes. destroy()

6. handleEvent() • This code is part of the AWT (1.0 Event Model) • public boolean handleEvent(Event evt) { • switch (evt.id) { • case Event.MOUSE_ENTER: return mouseEnter(evt, evt.x, evt.y); • case Event.MOUSE_EXIT: return mouseExit(evt, evt.x, evt.y); • case Event.MOUSE_MOVE: return mouseMove(evt, evt.x, evt.y); • case Event.MOUSE_DOWN: return mouseDown(evt, evt.x, evt.y); • case Event.MOUSE_DRAG: return mouseDrag(evt, evt.x, evt.y); • case Event.MOUSE_UP: return mouseUp(evt, evt.x, evt.y);

7. handleEvent() • case Event.KEY_PRESS: • case Event.KEY_ACTION: return keyDown(evt, evt.key); • case Event.KEY_RELEASE: • case Event.KEY_ACTION_RELEASE: return keyUp(evt, evt.key); • case Event.ACTION_EVENT: return action(evt, evt.arg); • case Event.GOT_FOCUS: return gotFocus(evt, evt.arg); • case Event.LOST_FOCUS: return lostFocus(evt, evt.arg); • } • return false; • }

8. Applets-Event handling • To react to an event, an applet must override either the appropriate event-specific method or the handleEvent method. • For example, adding the following code to the Simple applet makes it respond to mouse clicks. • import java.awt.Event; • . . . • public boolean mouseDown(Event event, int x, int y) { addItem("click!... "); • return true; • }

9. Servlets (JDK 1.2) • Servlets are modules that extend Java-enabled web servers. For example, a servlet might be responsible for taking data in an HTML order-entry form and applying the business logic used to update a company's order database. Servlets are to servers what applets are to browsers. Unlike applets, however, servlets have no graphical user interface. For a full tutorial, seehttp://java.sun.com/docs/books/tutorial/servlets/overview/index.html

10. Other uses of servlets • Allowing collaboration between people. • A servlet can handle multiple requests concurrently, and can synchronize requests. This allows servlets to support systems such as on-line conferencing. • Forwarding requests. • Servlets can forward requests to other servers and servlets. Thus servlets can be used to balance load among several servers that mirror the same content, and to partition a single logical service over several servers, according to task type or organizational boundaries.

11. Applets vs. Servlets

12. Servlet Lifecycle Chiamato solo la prima volta che la Servlet viene caricato in memoria! init() doXXX() doGet() service(HttpServletRequest r, HttpServletResponse p) doPost() Se la Servlet implements SingleThreadModel non ci saranno esecuzioni simultanee di codice Solo quando serve scaricare dalla memoria! destroy()

13. service() • This code is part of the class HttpService • protected void service (HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException { • Stringmethod = req.getMethod (); • if (method.equals ("GET")) { • longifModifiedSince = req.getDateHeader ("If-Modified-Since"); • longlastModified = getLastModified (req); • maybeSetLastModified (resp, lastModified); • if (ifModifiedSince == -1 || lastModified == -1)doGet (req, resp); • else { • longnow = System.currentTimeMillis (); • if (now < ifModifiedSince || ifModifiedSince < lastModified) • doGet (req, resp); • else • resp.sendError (HttpServletResponse.SC_NOT_MODIFIED); • }

14. service() • } else if (method.equals ("HEAD")) { • long lastModified; • lastModified = getLastModified (req); • maybeSetLastModified (resp, lastModified); • doHead (req, resp); • } else if (method.equals ("POST")) {doPost (req, resp); } • else if (method.equals ("PUT")) {doPut(req, resp); } • else if (method.equals ("DELETE")) {doDelete(req, resp); } • else if (method.equals ("OPTIONS")) {doOptions(req,resp); } • else if (method.equals ("TRACE")) {doTrace(req,resp); } • else { • resp.sendError (HttpServletResponse.SC_NOT_IMPLEMENTED, • "Method '" + method + "' is not defined in RFC 2068"); • } • }

15. A taste of servlet programming-1 • public class SimpleServlet extends HttpServlet { • /** Handle the HTTP GET method by building a simple web page. */ • public void doGet (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { • PrintWriter out; • String title = "Simple Servlet Output";

16. A taste of servlet programming-2 • // set content type and other response header fields first • response.setContentType("text/html"); • // then write the data of the response • out = response.getWriter(); out.println("<HTML><HEAD><TITLE>"); • out.println(title); • out.println("</TITLE></HEAD><BODY>"); out.println("<H1>" + title + "</H1>"); • out.println("<P>This is output from SimpleServlet."); out.println("</BODY></HTML>"); • out.close(); • } • }

17. Esempio: ShowParameters • package coreservlets; • import java.io.*; • import javax.servlet.*; • import javax.servlet.http.*; • import java.util.*; • public class ShowParameters extends HttpServlet { • public void doGet(HttpServletRequest request HttpServletResponse response) • throws ServletException, IOException { • response.setContentType("text/html"); • PrintWriter out = response.getWriter(); • String title = "Reading All Request Parameters"; • out.println(ServletUtilities.headWithTitle(title) + • "<BODY BGCOLOR=\"#FDF5E6\">\n" + • "<H1 ALIGN=CENTER>" + title + "</H1>\n" + • "<TABLE BORDER=1 ALIGN=CENTER>\n" + • "<TR BGCOLOR=\"#FFAD00\">\n" + • "<TH>Parameter Name<TH>Parameter Value(s)");

18. Esempio: ShowParameters • Enumeration paramNames = request.getParameterNames(); • while(paramNames.hasMoreElements()) { • String paramName = (String)paramNames.nextElement(); • out.print("<TR><TD>" + paramName + "\n<TD>"); • String[] paramValues = request.getParameterValues(paramName); • if (paramValues.length == 1) { • String paramValue = paramValues[0]; • if (paramValue.length() == 0) out.println("<I>No Value</I>"); • else out.println(paramValue); • } else { • out.println("<UL>"); • for(int i=0; i<paramValues.length; i++) {out.println("<LI>" +paramValues[i]); } • out.println("</UL>"); • } • } • out.println("</TABLE>\n</BODY></HTML>"); • }

19. Esempio: ShowParameters • public void doPost(HttpServletRequest request, • HttpServletResponse response) • throws ServletException, IOException { • doGet(request, response); • } • }

20. Esempio: ShowParameters • <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> • <HTML> • <HEAD> • <TITLE>A Sample FORM using POST</TITLE> • </HEAD> • <BODY BGCOLOR="#FDF5E6"> • <H1 ALIGN="CENTER">A Sample FORM using POST</H1> • <FORM ACTION="/servlet/coreservlets.ShowParameters“ METHOD="POST”> • Item Number: <INPUT TYPE="TEXT" NAME="itemNum"><BR> • Quantity: <INPUT TYPE="TEXT" NAME="quantity"><BR> • Price Each: <INPUT TYPE="TEXT" NAME="price" VALUE="$"><BR> • <HR> • First Name: <INPUT TYPE="TEXT" NAME="firstName"><BR> • Last Name: <INPUT TYPE="TEXT" NAME="lastName"><BR> • Middle Initial: <INPUT TYPE="TEXT" NAME="initial"><BR> • Shipping Address: • <TEXTAREA NAME="address" ROWS=3 COLS=40></TEXTAREA><BR>

21. Esempio: ShowParameters • Credit Card:<BR> • &nbsp;&nbsp;<INPUT TYPE="RADIO" NAME="cardType“ VALUE="Visa">Visa<BR> • &nbsp;&nbsp;<INPUT TYPE="RADIO" NAME="cardType" • VALUE="Master Card">Master Card<BR> • &nbsp;&nbsp;<INPUT TYPE="RADIO" NAME="cardType" • VALUE="Amex">American Express<BR> • &nbsp;&nbsp;<INPUT TYPE="RADIO" NAME="cardType“ VALUE="Discover">Discover<BR> • &nbsp;&nbsp;<INPUT TYPE="RADIO" NAME="cardType" • VALUE="Java SmartCard">Java SmartCard<BR> • Credit Card Number: • <INPUT TYPE="PASSWORD" NAME="cardNum"><BR> • Repeat Credit Card Number: • <INPUT TYPE="PASSWORD" NAME="cardNum"><BR><BR> • <CENTER><INPUT TYPE="SUBMIT" VALUE="Submit Order"></CENTER> • </FORM> • </BODY> • </HTML>

22. Cookies: perché? • Identificazione di un utente in una sessione di e-commerce. • Customizzazione di un sito • Pubblicità mirata • Eliminazione di username e password

23. Cookies: i metodi • public void setComment(String c) • public String getComment() • public void setVersion(int c) • public int getVersion () • Version 0: Netscape standard • Version 1: RFC 2109

24. Cookies: i metodi • public void setMaxAge(int c) • public int getMaxAge() • Positive value: secondi di vita • 0: delete cookie • Negative value: finchè dura la sessione del browser

25. Cookies: i metodi • public void setDomain(String c) • public String getDomain() • public void setPath(int c) • public int getPath()

26. Cookies: esempio • Cookie userCookie = new Cookie(“user”,”uid1234”); • userCookie.setMaxAge(60*60*24*365); • response.addCookie(userCookie);

27. SetCookies • import java.io.*; import javax.servlet.*; import javax.servlet.http.*; • /** Sets six cookies: three that apply only to the current session • * (regardless of how long that session lasts) and three that persist for an hour • * (regardless of whether the browser is restarted). • */ • public class SetCookies extends HttpServlet { • public void doGet(HttpServletRequest request, HttpServletResponse response) • throws ServletException, IOException { • for(int i=0; i<3; i++) { • // Default maxAge is -1, indicating cookie • // applies only to current browsing session. • Cookie cookie = new Cookie("Session-Cookie-" + i, • "Cookie-Value-S" + i); • response.addCookie(cookie);

28. SetCookies • cookie = new Cookie("Persistent-Cookie-" + i,"Cookie-Value-P" + i); • // Cookie is valid for an hour, regardless of whether • // user quits browser, reboots computer, or whatever. • cookie.setMaxAge(3600); • response.addCookie(cookie); • } • response.setContentType("text/html"); • PrintWriter out = response.getWriter(); • String title = "Setting Cookies"; • out.println (ServletUtilities.headWithTitle(title) + • "<BODY BGCOLOR=\"#FDF5E6\">\n" +"<H1 ALIGN=\"CENTER\">" • + title + "</H1>\n" +"There are six cookies associated with this page.\n" + • "</BODY></HTML>"); • } • }

29. ShowCookies • import java.io.*; import javax.servlet.*; import javax.servlet.http.*; • /** Creates a table of the cookies associated with the current page. */ • public class ShowCookies extends HttpServlet { • public void doGet(HttpServletRequest request, HttpServletResponse response) • throws ServletException, IOException { • response.setContentType("text/html"); • PrintWriter out = response.getWriter(); • String title = "Active Cookies"; • out.println(ServletUtilities.headWithTitle(title) + • "<BODY BGCOLOR=\"#FDF5E6\">\n" + • "<H1 ALIGN=\"CENTER\">" + title + "</H1>\n" + • "<TABLE BORDER=1 ALIGN=\"CENTER\">\n" + • "<TR BGCOLOR=\"#FFAD00\">\n" + • " <TH>Cookie Name\n" + " <TH>Cookie Value");

30. ShowCookies • Cookie[] cookies = request.getCookies(); • Cookie cookie; • for(int i=0; i<cookies.length; i++) { • cookie = cookies[i]; • out.println("<TR>\n" + • " <TD>" + cookie.getName() + "\n" + • " <TD>" + cookie.getValue()); • } • out.println("</TABLE></BODY></HTML>"); • } • }

31. Session tracking using cookies • String sessionID = makeUniqueString(); • Hashtable sessionInfo = new Hashtable(); • Hashtable globalTable = getTableStoringSession(); • globalTable.put(sessionID,sessionInfo); • Cookie sessionCookie=new Cookie(“SessionID”,sessionID); • sessionCookie.setPath(“/”); • response.addCookie(sessionCookie);

32. Session tracking API • HttpSession session = request.getSession(true); • ShoppingCart cart = (ShoppingCart)session.getValue(“carrello”); // 2.1 • // 2.2 (ShoppingCart)session.getAttribute(“carrello”); • if (cart==null) { • cart=new ShoppingCart(); • session.putValue(“carrello”,cart); //2.1 • //2.2 session.putValue(“carrello”,cart); • } • doSomeThingWith(cart);

33. Session tracking API • public void removeValue(String name); //2.1 • public void removeAttribute(String name); //2.2 • public String[] getValueNames() //2.1 • public Enumeration getAttributeNames() //2.2

34. Session tracking API • public long getCreationTime(); • public long getLastAccessdTime(); • Secondi dal 1.1.1970, mezzanotte • public void removeAttribute(String name); • public int getMaxInactiveInterval(); • public void setMaxInactiveInterval(int sec); • public void invalidate();

35. ShowSession • import java.io.*; import javax.servlet.*; import javax.servlet.http.*; • import java.net.*; import java.util.*; • /** Simple example of session tracking. */ • public class ShowSession extends HttpServlet { • public void doGet(HttpServletRequest request, HttpServletResponse response) • throws ServletException, IOException { • response.setContentType("text/html"); • PrintWriter out = response.getWriter(); • String title = "Session Tracking Example"; • HttpSession session = request.getSession(true); • String heading; • // Use getAttribute instead of getValue in version 2.2. • Integer accessCount = (Integer)session.getValue("accessCount");

36. ShowSession • if (accessCount == null) { • accessCount = new Integer(0); • heading = "Welcome Newcomer"; • } else { • heading = "Welcome Back"; • accessCount = new Integer(accessCount.intValue() + 1); • } • // Use setAttribute instead of putValue in version 2.2. • session.putValue("accessCount", accessCount);

37. ShowSession • out.println(ServletUtilities.headWithTitle(title) + • "<BODY BGCOLOR=\"#FDF5E6\">\n" + • "<H1 ALIGN=\"CENTER\">" + heading + "</H1>\n" + • "<H2>Information on Your Session:</H2>\n" + • "<TABLE BORDER=1 ALIGN=\"CENTER\">\n" + • "<TR BGCOLOR=\"#FFAD00\">\n" + • " <TH>Info Type<TH>Value\n" + • "<TR>\n" +" <TD>ID\n" +" <TD>" + session.getId() + "\n" + • "<TR>\n" +" <TD>Creation Time\n" + • " <TD>" + new Date(session.getCreationTime()) + "\n" + • "<TR>\n" +" <TD>Time of Last Access\n" + • " <TD>" +new Date(session.getLastAccessedTime()) + "\n" + • "<TR>\n" +" <TD>Number of Previous Accesses\n" +" <TD>" + • accessCount + "\n" + "</TABLE>\n" +"</BODY></HTML>"); • }

38. ShowSession • /** Handle GET and POST requests identically. */ • public void doPost(HttpServletRequest request, • HttpServletResponse response) • throws ServletException, IOException { • doGet(request, response); • } • }

39. Simple.jsp • <html> • <body> • <% out.println(“Hello World”); %> • </body> • </html>

40. JSP Lifecycle Server Web Pagina JSP Servlet generato Browser Servlet compilato

41. Direttive • <%@ DIRETTIVA {attributo=valore} %> • Esempi: • <%@ page language=java %> • <%@ page import=java.awt.*,java.util.* session=true %>

42. Dichiarazioni • <%! DICHIARAZIONE %> • Esempi: • <%! String nome=pippo %> • <%! public String getName() {return nome} %>

43. Espressioni • <%= ESPRESSIONE%> • Esempi: • <%= getName() %> • <%@ page import=java.util.* %> • Sono le <%= new Date().toString(); %>

44. Esempio • <html><body> • <%! String nome=pippo %> • <%! public String getName() {return nome} %> • <H1> • Buongiorno • <%= getName() %> • </H1> • </body></html>

45. Azioni • <jsp:AZIONE> • Esempi: • <jsp:forward page=URL> • <jsp:include page=URL flush=true> • <jsp:useBean>

46. Scriptlet • <% SCRIPTLET %> • Esempi: • <% z=z+1; %> • <% • // Get the Employee's Name from the request • out.println("<b>Employee: </b>" + • request.getParameter("employee")); • // Get the Employee's Title from the request • out.println("<br><b>Title: </b>" + • request.getParameter("title")); • %>

47. Oggetti predefiniti • out Writer • request HttpServletRequest • response HttpServletResponse • session HttpSession • page this nel Servlet • application servlet.getServletContext • area condivisa tra i servlet • config ServletConfig • exception solo nella errorPage • pageContext sorgente degli oggetti, raramente usato

48. request • <%@ page errorPage="errorpage.jsp" %> • <html> • <head> • <title>UseRequest</title> • </head> • <body> • <% • // Get the User's Name from the request • out.println("<b>Hello: " + request.getParameter("user") + "</b>"); • %> • </body> • </html>

49. session • <%@ page errorPage="errorpage.jsp" %> • <html> <head> <title>UseSession</title> </head> • <body> • <% • // Try and get the current count from the session • Integer count = (Integer)session.getAttribute("COUNT"); • // If COUNT is not found, create it and add it to the session • if ( count == null ) { • count = new Integer(1); • session.setAttribute("COUNT", count); • }

50. session • else { • count = new Integer(count.intValue() + 1); • session.setAttribute("COUNT", count); • } • // Get the User's Name from the request • out.println("<b>Hello you have visited this site: " • + count + " times.</b>"); • %> • </body> • </html>