Applets, Servlets e JSP

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Marco Ronchetti -ronchet@altavista.it

Applets, Servlets e JSP

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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).

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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.

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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()

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Applet Lifecycle

Whenever it’s needed, at lower priority

init()

stop() destroy()

start()

handleEvent()

Multithreading!

Actually, more threads are active behind the scenes.

paint()

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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);

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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;

}

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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;

}

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Applets

Le applets sono uno scheletro di applicazione che gira nello spazio concesso loro da un browser.

Il programmatore ha la responsabilita’ di implementare i seguenti metodi (che possono anche essere lasciati vuoti):

NOTA: il programmatore puo’ notificare la necessita’ di ridisegnare la applet tramite la chiamata repaint().

Tuttavia, l’effettivo ridisegno verra’ fatto dal sistema SOLO quando vi saranno risorse disponibili! (vedi Threads).

init() viene eseguito quando la applet viene creata start() viene eseguito quando la applet (ri)parte

stop() viene eseguito quando la applet viene fermata destroy() viene eseguito quando la applet viene distrutta

paint() viene eseguito quando la applet viene (ri)disegnata

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Applet methods - 1a

import java.awt.Graphics;

import java.util.Date;

public class ShowAppletMethods extends java.applet.Applet { Date d;

int count=0;

public void init() {

System.out.println((count++)+" Init Executed");

}

public void start() {

System.out.println((count++)+" Start Executed");

}

public void stop() {

System.out.println((count++)+" Stop Executed");

}

public void destroy() {

System.out.println((count++)+" Destroy Executed");

}

public void paint(Graphics g) {

System.out.println((count++)+" Paint Executed");

d=new Date();

g.drawString("Time now is "+d.getHours() +":” +d.getMinutes() +":” +d.getSeconds(), 5, 25);

} }

<TITLE>Another Applet</TITLE>

</HEAD>

<BODY>

<APPLET

CODE="ShowAppletMethods.class"

WIDTH=200 HEIGHT=75>

</APPLET>

</BODY></HTML>

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Elementi Grafici

import java.awt.*;

import java.awt.event.*;

public class TestPattern extends java.applet.Applet { int theta = 45;

public void paint( Graphics g ) { int Width = size().width;

int Height = size().height;

int width = Width/2;

int height = Height/2;

int x = (Width - width)/2;

int y = (Height- height)/2;

int [] polyx = { 0, Width/2, Width, Width/2 };

int [] polyy = { Height/2, 0, Height/2, Height };

Polygon poly = new Polygon( polyx, polyy, 4 );

g.setColor( Color.black );

g.fillRect( 0, 0, size().width, size().height );

g.setColor( Color.yellow );

g.fillPolygon( poly );

g.setColor( Color.red );

g.fillRect( x, y, width, height );

g.setColor( Color.green );

g.fillOval( x, y, width, height );

g.setColor( Color.blue );

int delta = 90;

g.fillArc( x, y, width, height, theta, delta );

g.setColor( Color.white );

g.drawLine( x, y, x+width, x+height );

}

public void init() { addMouseListener(

new MouseAdapter() {

public void mousePressed(

MouseEvent e ) {

theta= theta+10)%360;

repaint();

} } );

} }

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Metodi grafici di Graphics

draw3DRect() Draws a highlighted, 3D rectangle drawArc() Draws an arc

drawLine() Draws a line drawOval() Draws an oval

drawPolygon() Draws a polygon, connecting endpoints drawPolyline() Draws a line connecting a polygon's points drawRect() Draws a rectangle

drawRoundRect() Draws a rounded-corner rectangle

fill3DRect() Draws a filled, highlighted, 3D rectangle fillArc() Draws a filled arc

fillOval() Draws a filled oval fillPolygon() Draws a filled polygon fillRect() Draws a filled rectangle

fillRoundRect() Draws a filled, rounded-corner rectangle

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Text & Fonts

import java.awt.Font; import java.awt.Graphics; import java.awt.FontMetrics;

public class ManyFonts extends java.applet.Applet { public void paint(Graphics g) {

Font f = new Font("TimesRoman", Font.PLAIN, 18);

FontMetrics fm = getFontMetrics(f);

g.setFont(f);

String s = "This is a plain font";

int xstart = (size().width - fm.stringWidth(s)) / 2;

//int ystart = (size().height + fm.getHeight()) / 2;

g.drawString(s, xstart, 25);

Font fb = new Font("TimesRoman", Font.BOLD, 18);

Font fi = new Font("TimesRoman", Font.ITALIC, 18);

Font fbi = new Font("TimesRoman", Font.BOLD + Font.ITALIC, 18);

g.setFont(fb);

g.drawString("This is a bold font", 10, 50);

g.setFont(fi);

g.drawString("This is an italic font", 10, 75);

g.setFont(fbi);

g.drawString("This is a bold italic font", 10, 100);

} }

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Colore

import java.awt.Graphics;

import java.awt.Color;

public class ColorBoxes extends java.applet.Applet {

public void paint(Graphics g) { int rval, gval, bval;

for (int j = 30; j < (this.size().height -25); j += 30) for (int i = 5; i < (this.size().width -25); i+= 30) { rval = (int)Math.floor(Math.random() * 256);

gval = (int)Math.floor(Math.random() * 256);

bval = (int)Math.floor(Math.random() * 256);

g.setColor(new Color(rval,gval,bval));

g.fillRect(i,j,25,25);

g.setColor(Color.black);

g.drawRect(i-1,j-1,25,25);

} } }

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Applet methods - 2

int count=0;

int seconds;

seconds=Integer.parseInt(this.getParameter("Secondi"));

}

while (true) { try {

Thread.sleep(seconds*1000);

}

catch (InterruptedException e) {}

System.out.println("==> calling repaint");

repaint();

} }

}

public void destroy() {

}

d=new Date();

g.drawString("Time now is ” +d.getHours() +":”

+d.getMinutes() +":” +d.getSeconds(), 5, 25);

} }

<HTML><HEAD>

<TITLE>Another Applet</TITLE>

</HEAD><BODY>

<APPLET CODE="ShowAppletMethods.class"

WIDTH=200 HEIGHT=75>

<PARAM name=secondi value=10>

</APPLET>

</BODY></HTML>

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Multithreading per la paint()

La versione precedente del codice non disegna MAI lo schermo!

Il problema e’ che il programma ha una singola thread,

che e’ sempre occupata: nessuno quindi puo’ eseguire la paint().

La soluzione e’ di creare una nuova thread che faccia il lavoro

vero e proprio, lasciando alla applet meno compiti.

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Applet methods - 3

int count=0;

simpleThread t;

int seconds=Integer.parseInt(this.getParameter(

"Secondi"));

t=new simpleThread(this,seconds);

t.start();

}

public void destroy() { t.stop();

}

d=new Date();

g.drawString("Time now is "+d.getHours() +":” +d.getMinutes() +":” +d.getSeconds(), 5, 25);

}

class simpleThread extends Thread { ShowAppletMethods a;

int seconds;

simpleThread(ShowAppletMethods a, int s) { this.a=a;

seconds=s*1000;

}

public void run() { while (true) {

try {

sleep(seconds);

}

catch (InterruptedException e) {}

System.out.println("==> THREAD: calling repaint");

a.repaint();

} } }

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Double buffering

Le animazioni vengono effettuate cancellando l’immagine presente e ridisegnando la nuova. Questo da’ origine ad un fastidioso sfarfallio.

Per evitare questo effetto, la nuova immagine viene disegnata in memoria anziche’ a video: quando l’immagine e’ pronta, quella presente a video viene sostituita con la nuova (tecnica di double buffering).

La tecnica si basa sulla ridefinizione del metodo “update()” che viene chiamato dalla repaint(), e che a sua volta schedula la paint(). La versione standard di update e’ :

public void update(Graphics g) { g.setColor(getBackground());

g.fillRect(0,0,width,height);

g.setColor(getForeground());

paint(g);

}

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Animazione con flickering

/* simple applet to show very basic startup and animation stuff */

import java.awt.Color;

public class Checkers extends java.applet.Applet implements Runnable {

Thread runner;

int xpos;

public void start() { if (runner == null); {

runner = new Thread(this);

runner.start();

} }

public void stop() { if (runner != null) {

runner.stop();

runner = null;

} }

for (xpos = 5; xpos <= 105; xpos+=4) { repaint();

try { Thread.sleep(100); }

catch (InterruptedException e) { } }

xpos=5;

} }

public void update(Graphics g) { paint(g);

}

public void paint(Graphics g) { // Draw background

g.setColor(Color.black);

g.fillRect(0,0,100,100);

g.setColor(Color.white);

g.fillRect(100,0,100,100);

// Draw checker

g.setColor(Color.red);

g.fillOval(xpos,5,90,90);

} }

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Animazione senza flickering

import java.awt.Color;

import java.awt.Image;

public class Checkers2 extends java.applet.Applet implements Runnable {

Thread runner;

int xpos;

Image offscreenImg;

Graphics offscreenG;

offscreenImg = createImage(this.size().width, this.size().height);

offscreenG = offscreenImg.getGraphics();

}

public void start() { if (runner == null); {

runner = new Thread(this);

runner.start();

} }

public void stop() { if (runner != null) {

runner.stop();

runner = null;

} }

for (xpos = 5; xpos <= 105; xpos+=4) { repaint();

try { Thread.sleep(100); }

catch (InterruptedException e) { } }

xpos = 5;

} }

public void update(Graphics g) { paint(g);

}

public void paint(Graphics g) { // Draw background

offscreenG.setColor(Color.black);

offscreenG.fillRect(0,0,100,100);

offscreenG.setColor(Color.white);

offscreenG.fillRect(100,0,100,100);

// Draw checker

offscreenG.setColor(Color.red);

offscreenG.fillOval(xpos,5,90,90);

g.drawImage(offscreenImg,0,0,this);

}

public void destroy() { offscreenG.dispose();

} }

NOTA: I contesti grafici non vengono liberati dalla garbage collection, vanno rilasciati esplicitamente! (Vedi destroy)

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Launching Applets as Apps

class AppletFrame extends Frame implements ActionListener { public AppletFrame (String title, Applet applet,

int width, int height) { //create Frame with specified title

super(title);

//add a Menubar

MenuBar menubar=new MenuBar();

Menu file = new Menu("File",true);

menubar.add(file);

MenuItem mExit=new MenuItem("Exit");

file.add(mExit);

mExit.addActionListener(this);

this.setMenuBar(menubar);

import java.awt.*;

import java.applet.*;

public class ShowAppletMethodsAsApplication extends ShowAppletMethods { public static void main(String args[]) {

Applet applet=new ShowAppletMethodsAsApplication();

Frame frame=new AppletFrame("ShowAppletMethodsAsApplication",applet,300,300);

} }

// add the applet to the window, // set window size, show it

this.add("Center",applet);

this.resize(width,height);

this.show();

//Start the applet applet.init();

applet.start();

}

public void actionPerformed(ActionEvent e) System.exit(0);

}

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Applets and the status line

Applets display status lines with the showStatus method.

showStatus("MyApplet: hello!");

The status line is not usually very prominent, and it can be overwritten by other applets or by the browser. For these reasons, it's best used

for incidental, transitory information.

Note: Please don't put scrolling text in the status line. Browser users

find such status line abuse highly annoying!

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Applets and HTML text

With the AppletContext showDocument method, an applet can tell the browser which URL to show and

in which browser window.

public void showDocument(java.net.URL url, String targetWindow)

For a full example, see

http://java.sun.com/docs/books/tutorial/applet/appletsonly/browser.html

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Interaction among applets

Applets can find other applets and send messages to them, with the following security restrictions:

Many browsers require that the applets originate from the same server.

Many browsers require that the applets originate from the same directory on the server (the same code base).

The Java API requires that the applets be running on the same page, in the same browser window.

For a full example, see

http://java.sun.com/docs/books/tutorial/applet/appletsonly/iac.html

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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, see

http://java.sun.com/docs/books/tutorial/servlets/overview/index.html

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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.

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Applets vs. Servlets

NO SI

Grafica

javax.servlet.http.

HttpServlet java.applet.Applet

Estende:

service() handleEvent()

Cuore:

NO NO

Ha un main:

Server Client

Gira:

Applet Servlet

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Servlet Lifecycle

init()

destroy()

service(HttpServletRequest r, HttpServletResponse p)

Chiamato solo la prima volta che la Servlet viene caricato in memoria!

doGet() doPost() doXXX()

Solo quando serve scaricare dalla memoria!

Se la Servlet implements SingleThreadModel non

ci saranno esecuzioni simultanee di codice

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service()

This code is part of the class HttpService

protected void service (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException

{

String method = req.getMethod ();

if (method.equals ("GET")) {

long ifModifiedSince; long lastModified; long now;

ifModifiedSince = req.getDateHeader ("If-Modified-Since");

lastModified = getLastModified (req);

maybeSetLastModified (resp, lastModified);

if (ifModifiedSince == -1 || lastModified == -1) doGet (req, resp);

else {

now = System.currentTimeMillis ();

if (now < ifModifiedSince || ifModifiedSince < lastModified) doGet (req, resp);

else

resp.sendError (HttpServletResponse.SC_NOT_MODIFIED);

}

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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");

} }

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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";

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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();

}

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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(“<HEAD><TITLE>”+title + “</TITLE> </HEAD>”)+

"<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)");

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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>");

}

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Esempio: ShowParameters

public void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException { doGet(request, response);

} }

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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>

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Esempio: ShowParameters

Credit Card:<BR>

  <INPUT TYPE="RADIO" NAME="cardType“

VALUE="Visa">Visa<BR>

  <INPUT TYPE="RADIO" NAME="cardType"

VALUE="Master Card">Master Card<BR>

VALUE="Amex">American Express<BR>

  <INPUT TYPE="RADIO" NAME="cardType“

VALUE="Discover">Discover<BR>

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>

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Cookies: perché?

Identificazione di un utente in una sessione di e-commerce.

Customizzazione di un sito Pubblicità mirata

Eliminazione di username e password

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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

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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

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Cookies: i metodi

public void setDomain(String c) public String getDomain()

public void setPath(int c)

public int getPath()

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Cookies: esempio

Cookie userCookie = new Cookie(“user”,”uid1234”);

**userCookie.setMaxAge(606024*365);**

response.addCookie(userCookie);

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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);

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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);

}

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>");

} }

SetCookies

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/** Creates a table of the cookies associated with the current page. */

public class ShowCookies extends HttpServlet {

String title = "Active Cookies";

out.println(ServletUtilities.headWithTitle(title) +

"<H1 ALIGN=\"CENTER\">" + title + "</H1>\n" +

"<TABLE BORDER=1 ALIGN=\"CENTER\">\n" +

" <TH>Cookie Name\n" + " <TH>Cookie Value");

ShowCookies

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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>");

} }

ShowCookies

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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);

Session tracking using cookies

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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);

Session tracking API

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public void removeValue(String name); //2.1

public void removeAttribute(String name); //2.2

public String[] getValueNames() //2.1 public Enumeration getAttributeNames() //2.2

Session tracking API

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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();

Session tracking API

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import java.net.*; import java.util.*;

/** Simple example of session tracking. */

public class ShowSession extends HttpServlet {

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");

ShowSession

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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);

ShowSession

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out.println(ServletUtilities.headWithTitle(title) +

"<H1 ALIGN=\"CENTER\">" + heading + "</H1>\n" +

"<H2>Information on Your Session:</H2>\n" +

"<TABLE BORDER=1 ALIGN=\"CENTER\">\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>");

}

ShowSession

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/ Handle GET and POST requests identically. */**

public void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException { doGet(request, response);

} }

ShowSession

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<html>

<body>

<% out.println(“Hello World”); %>

</body>

</html>

Simple.jsp

(56)

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JSP Lifecycle

Browser Servlet generato

Servlet compilato

Pagina JSP

Server Web

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<%@ DIRETTIVA {attributo=valore} %>

Esempi:

<%@ page language=java %>

**<%@ page import=java.awt.,java.util. session=true**

%>

Direttive

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<%! DICHIARAZIONE %>

Esempi:

<%! String nome=pippo %>

<%! public String getName() {return nome} %>

Dichiarazioni

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<%= ESPRESSIONE%>

Esempi:

<%= getName() %>

**<%@ page import=java.util.* %>**

Sono le <%= new Date().toString(); %>

Espressioni

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<html><body>

<%! String nome=pippo %>

<%! public String getName() {return nome} %>

<H1>

Buongiorno

<%= getName() %>

</H1>

</body></html>

Esempio

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<jsp:AZIONE>

Esempi:

<jsp:forward page=URL>

<jsp:include page=URL flush=true>

<jsp:useBean>

Azioni

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<% 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"));

%>

Scriptlet

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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

Oggetti predefiniti

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<%@ 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>

request

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