EA-SI-0910p4jfc/ensino/EA-SI/0910-Aula07.pdf · 5/10/10 3 Engenharia de Aplicações –...

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Engenharia de Aplicações – Sistemas Interactivos 2009/10!

Mestrado em Informática – Universidade do Minho! 6!

Implementação



Building web Apps

  How to create dynamic contents?"  Client side"

-  Code runs on the client (browser)"  JavaScript (client side), DHTML (Dynamic HTML), AJAX, VBScript"

-  Code runs on a “virtual machine” (in the browser)"  Java applets, Adobe Flex, Microsoft Silverlight, JavaFX"

  Server side"-  Code runs on the server"

  Perl, ASP, PHP, Servlets, JavaScript (server side), JSP, JSF"-  CGI vs. direct execution"



Server vs. client side

  Server side"-  access to information and functions available on the server. "-  require interpreter on the server, "-  largely independent from browser, or other client details. "

  Client side"-  access to information and functions available on the browser"-  require interpreter on the browser "-  no additional software on the server (popular with authors who lack

administrative access to their servers);"-  problems with lack of standardization of browsers "

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Common Gateway Interface (CGI)   Early form of server side scripting"

  Protocol for interfacing external applications with a web server"

  When request received, corresponding program called"

  The protocol defines "

-  how information about the server and the request is passed to the command (arguments and environment variables) "

-  how the command can pass back extra information about the output (headers)"



CGI programming

  all output from CGI program must be preceded by a MIME-type header"

  output needs to be in HTML"-  or some other format that a browser will be able to

display"

#!/usr/bin/perl

print "Content-type: text/html\n\n"; print "Olá, Mundo!";



CGI programming

  all output from CGI program must be preceded by a MIME-type header"

  output needs to be in HTML"-  or some other format that a browser will be able to

display"

#!/usr/bin/perl

print "Content-type: text/html\n\n"; print "Olá, Mundo!";

#!/usr/bin/perl

use CGI ':standard';

$q = new CGI; $nome = $q->param('nome');

print header("text/html");

print "<html>"; print "Olá, $nome!"; print "</html>";

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CGI?

  Language independent approach"-  Any program that the server can run can be used"-  Programs only need to output text"

  Low-tech approach"-  Inefficient from time and memory perspective"-  Can quickly overwhelm web servers"



Direct execution

  Applications run on web server instead of OS"-  Apache modules (PHP, …)"-  Apache Tomcat (JSP)"-  ASP .NET"-  Internet Server Application Programming Interface (ISAPI)"

  Application servers"-  Move back towards mainframe computing"-  Server stores business logic and user interface"-  Client side runs on a browser"



Servlets

  Tecnologia Java"  Geração de HTML

on the fly!  Nova vista (página)

gerada a cada pedido"-  Vista é programada, não

desenhada"-  Não encorajam separação

entre apresentação e negócio/conteúdo"

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JSP (Java Server Pages)

  Permite incluir código Java nas páginas HTML"  Ficheiros .jsp compilam para Java"

-  ou directamente para bytecode"-  on interpretados on the fly…"

  Código Java compilado e executado para gerar HTML"

  Um salto de abstracção em relação às Servlets"



JSP: Expressões

  <%= expressão Java %>"

  Expressão avaliada em run time "

<HTML> <BODY> Hello! The time is now <%= new java.util.Date() %> </BODY>

</HTML>



JSP: Scriptlets

  <% bloco de código Java %>"

  Por si só uma Scriptlet não produz HTML"-  mas podemos programá-la para isso…"

<HTML> <BODY> <% System.out.println( "Evaluating date now" );

java.util.Date date = new java.util.Date(); %> Hello! The time is now <%= date %> </BODY>

</HTML>

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JSP: Algumas variáveis

  out: javax.servlet.jsp.JspWriter"-  Para “escrever” na página"

  request: javax.servlet.http.HttpServletRequest"-  informação sobre o pedido enviado pelo browser"

  response: javax.servlet.http.HttpServletResponse"-  resposta a enviar ao browser"

Hello! Your address is: <% out.println( request.getRemoteHost());%>

http://java.sun.com/products/servlet/2.2/javadoc/

Hello! The time is now <% out.println( String.valueOf( date )); %>



JSP: Misturar HTML e Java

  Melhor que utilizar out é misturar HTML e Java"<table border=2>

<% for ( int i = 0; i < n; i++ ) { %> <tr> <td>Number</td> <td><%= i+1 %></td> </tr> <%}%> </table>



JSP: Directivas

  <%@ tipo atributo%>"-  tipo: page/include/taglib/…"

  Directiva page: informação sobre a servlet a gerar"-  import/contentType/pageEncoding/session/errorPage/…"

  Directiva include: "

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

<BODY> Hello! The time is now <%= new Date() %> </BODY>

</HTML>

<%@ include file="relativeURL" %>

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JSP: Declarações

  <%! declarações Java %>"

  Mas agora não funciona! (class level scope)"

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

<BODY> <%!

Date theDate = new Date(); Date getDate() { System.out.println( "In getDate() method" ); return theDate; }

%> Hello! The time is now <%= getDate() %> </BODY>

</HTML>



JSP: tags

  tags pré-definidas"-  <jsp:tag>…</jsp:tag>"-  text/include/forward/useBean/getProperty/

setProperty/plugin"  tags de bibliotecas externas (taglibs)"

-  Directiva taglib"

<%@ taglib uri="URIForLibrary" prefix="tagPrefix" %>



JSP: Sessões

  Variável: session"-  um(a espécie de) Map "-  permite guardar informação de página para página"

session.setAttribute("theName", name); session.getAttribute("theName”);

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Links Úteis

  http://java.sun.com/products/jsp/"  http://java.sun.com/products/jsp/syntax/2.0/card20.pdf"  http://www.jsptut.com/"

EA-SI-0910p4jfc/ensino/EA-SI/0910-Aula07.pdf · 5/10/10 3 Engenharia de Aplicações –...

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