Varför bygga sidor dynamiskt?

Basic Internet Programming 2004
Servlets, Cookies and Sessions
Björn Eiderbäck
bjorne@nada.kth.se
Cristian Bogdan
cristi@nada.kth.se
Š Introduktion
Š Pragmatisk exempelorienterad beskrivning
ŠLänkar på nätet
Basic Internet Programming
Servlets
Varför bygga sidor dynamiskt?
Š Websidorna baseras på data från användarna
Š Websidorna konstrueras från data som ändras
ofta
Š Websidorna använder information från
databaser, andra program på nätet eller via
andra serverresurser
1
Basic Internet Programming
Servlets
Vad är servlets?
Š Servlets är program körs på serversidan
Š Motsvarar ungefär CGI-bin, dvs program som kör på
servern skrivna i diverse olika språk
Š En servlet
„
„
„
„
Läser data från klienter
Genererar svar
Skickar data tillbaks till klienter
Kommunicerar med filer, databaser och andra program
Basic Internet Programming
Servlets
Hur kör jag servlets?
Š En servlet körs i en Container av typ Tomcat
Š En servlet anropas från en webläsare eller
från en form i en html/xhtml-sida
2
Basic Internet Programming
Servlets
Fördelar med servlets jämfört
med cgi-bin
Š Effektivt
„
Trådar istället för OS-processer
Š Bekvämt
„
Massor med högnivåfaciliteter
Š Kraftfullt
„
Dela data, poolning, persistens
Š Portabelt
„
Kan köras på massor av plattformar och servrar
Š Säkert
„
Körs i ”sandlåda”, ingen overflow
Š Ej dyrt
Basic Internet Programming
Servlets
En servlets struktur
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class ServletTemplate extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws
ServletException, IOException {
// Use "request" to read incoming HTTP headers
// (e.g., cookies) and query data from HTML forms.
// Use "response" to specify the HTTP response status
// code and headers (e.g. the content type, cookies).
PrintWriter out = response.getWriter();
// Use "out" to send content to browser
}
}
3
Basic Internet Programming
Servlets
En enkel servlet som genererar
text
import java.io.*; import javax.servlet.*; import
javax.servlet.http.*;
public class HelloWorld extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
/* servlet container takes care of writing
initial http header lines. Still, we can change
headers: */
response.setContentType("text/plain");
/* now the content: */
PrintWriter out = response.getWriter();
out.println("Hello World");
}
}
Basic Internet Programming
Servlets
Kompilera
Š Lägg in följande i CLASSPATH
„
%CATALINA_HOME%\common\lib\servlet.jar
z
Servletklasserna ligger i servlet.jar, så dom måste med
Š Kompilera med javac
„
„
javac MinServlet.java
Alternativt om inte CLASSPATH är satt kan man göra
något i stil med
javac –classpath ".;%CATALINA_HOME%\common\lib\servlet.jar" MinServlet.java
Sök i aktuell
katalog
Använd klasser i servlet.jar
placerad i Tomcats lib
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Basic Internet Programming
Servlets
Managing tomcat via ant
Š Sets the classpath and other tomcat environment for you
Š Works on all Windows and Unix/Mac OS X platforms
~> mkdir test; cd test
~/test> (set the path to ant)
~/test> cp -r /info/intnet03/localTomcat/ .
~/test> cd localTomcat/
localTomcat> ant install
localTomcat> ant compile
localTomcat> ant tomcat
localTomcat> ant stopTomcat
Basic Internet Programming
Servlets
Standard Web Application
(webapp) Directories
Under webapps/ everything is tomcat-independent!
webapps/
ROOT/
examples/
WEB-INF/…
(servlet contexts)
http://host:port/
http://host:port/examples
(not visible by http)
http://host:port/labbar
http://host:port/labbar/test.html
(not visible by http)
labbar/
test.html, test.jsp foo/bar.html
WEB-INF/
web.xml
someJSPTagLibrary.tld
classes/
HelloWoldServlet.java HelloWorldServlet.class
somepackage/AClassInThePackage
lib/
someLibrary.jar
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Basic Internet Programming
Servlets
En servlet som genererar
HTML
import java.io.*; import javax.servlet.*; import
javax.servlet.http.*;
public class HelloWWW extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)throws
ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String docType =
"<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0 " +
"Transitional//EN\">\n";
out.println(docType +
"<HTML>\n" +
"<HEAD><TITLE>Hello WWW</TITLE></HEAD>\n" +
"<BODY>\n" +
"<H1>Hello WWW</H1>\n" +
"</BODY></HTML>");}}
Basic Internet Programming
Servlets
En användbar klass för att
skapa HTML-header
public class ServletUtilities {
public static final String DOCTYPE =
"<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0 " +
"Transitional//EN\">";
public static String headWithTitle(String title) {
return(DOCTYPE + "\n" +
"<HTML>\n" +
"<HEAD><TITLE>" + title +
"</TITLE></HEAD>\n");
}
//Resten av klassen behövs inte nu, så den utelämnar vi
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Basic Internet Programming
Servlets
En klass som använder
föregående klass
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class SimplerHelloWWW extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println(ServletUtilities.headWithTitle("Hello WWW") +
"<BODY>\n" +
"<H1>Hello WWW</H1>\n" +
"</BODY></HTML>");
}
}
Basic Internet Programming
Servlets
Lifscykel
Lifscykel
Š init anropas då servleten skapas
public void init() throws ServletException
{ //Initiera servleten, tex genom att läsa in data från
databas
}
Š service
„
Varje gång en server får en fråga skapas en ny tråd och anropar
service
Š doGet, doPost och doXxx
„
Dessa metoder är dom man normalt själv skriver för att beskriva vad
servleten ska göra vid respektive anrop
Š Vi tittar i Suns tutorial som beskriver detta
„
http://java.sun.com/docs/books/tutorial/servlets/index.html
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Basic Internet Programming
Servlets
Initieringsparametrar,
Initieringsparametrar, servlet
servlet
public class ShowMessage extends HttpServlet {
private String message;
private String defaultMessage = "No message.";
private int repeats = 1;
public void init() throws ServletException {
ServletConfig config = getServletConfig();
message = config.getInitParameter("message");
if (message == null) {
message = defaultMessage;
}
Basic Internet Programming
Servlets
...
try {
String repeatString =
config.getInitParameter("repeats");
repeats = Integer.parseInt(repeatString);
} catch(NumberFormatException nfe) {
/* NumberFormatException handles case where
repeatString is null *and* case where it is in an
illegal format. */
}
}
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Basic Internet Programming
Servlets
...
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String title = "The ShowMessage Servlet";
out.println(ServletUtilities.headWithTitle(title) +
"<BODY BGCOLOR=\"#FDF5E6\">\n" +
"<H1 ALIGN=\"CENTER\">" + title +
"</H1>");
for(int i=0; i<repeats; i++) {
out.println("<B>" + message + "</B><BR>");
}
out.println("</BODY></HTML>");
}
}
Basic Internet Programming
Servlets
... Initieringsparametrar,
web.xml
<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE web-app
PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application
2.2//EN"
"http://java.sun.com/j2ee/dtds/web-app_2.2.dtd">
<web-app>
<servlet>
<servlet-name>ShowMsg</servlet-name>
<servlet-class>ShowMessage</servlet-class>
<init-param>
<param-name>message</param-name>
<param-value>Shibboleth</param-value>
</init-param>
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Basic Internet Programming
Servlets
...
<init-param>
<param-name>repeats</param-name>
<param-value>5</param-value>
</init-param>
</servlet>
</web-app>
Basic Internet Programming
Servlets
Anropa servlet med parametrar,
htmldel
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<!-Front end to ThreeParams servlet.
Taken from Core Web Programming Java 2 Edition
from Prentice Hall and Sun Microsystems Press,
http://www.corewebprogramming.com/.
May be freely used or adapted.
-->
<HTML>
<HEAD>
<TITLE>Collecting Three Parameters</TITLE>
</HEAD>
<BODY BGCOLOR="#FDF5E6">
<H1 ALIGN="CENTER">Collecting Three Parameters</H1>
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Basic Internet Programming
Servlets
...
<FORM ACTION="/servlet/ThreeParams">
First Parameter: <INPUT TYPE="TEXT" NAME="param1"><BR>
Second Parameter: <INPUT TYPE="TEXT”
NAME="param2"><BR>
Third Parameter: <INPUT TYPE="TEXT" NAME="param3"><BR>
<CENTER><INPUT TYPE="SUBMIT"></CENTER>
</FORM>
</BODY>
</HTML>
Basic Internet Programming
Servlets
Anropa
Anropa servlet
servlet med
med parametrar,
parametrar,
servletdel
servletdel
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class ThreeParams extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String title = "Reading Three Request
Parameters";
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Basic Internet Programming
Servlets
...
out.println(ServletUtilities.headWithTitle(title) +
"<BODY BGCOLOR=\"#FDF5E6\">\n" +
"<H1 ALIGN=\"CENTER\">" + title + "</H1>\n" +
"<UL>\n" +
" <LI><B>param1</B>: "
+ request.getParameter("param1") + "\n" +
" <LI><B>param2</B>: "
+ request.getParameter("param2") + "\n" +
" <LI><B>param3</B>: "
+ request.getParameter("param3") + "\n" +
"</UL>\n" +
"</BODY></HTML>");
}
}
Basic Internet Programming
Servlets
Request
Request headers
headers
Š Med servleten kommer massa information
via HTTP-protokollet.
Š Vi kan läsa av hur servleten anropades (GET
eller POST), vilken URI som angavs, vilka
browser klienten har, vilken dator som
klienten befinner sig på och en del annat
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Basic Internet Programming
Servlets
... exempel
public class ShowRequestHeaders extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String title = "Servlet Example: Showing Request
Headers";
Basic Internet Programming
Servlets
...
out.println(ServletUtilities.headWithTitle(title) +
"<BODY BGCOLOR=\"#FDF5E6\">\n" +
"<H1 ALIGN=\"CENTER\">" + title +
"</H1>\n" +
"<B>Request Method: </B>" +
request.getMethod() + "<BR>\n" +
"<B>Request URI: </B>" +
request.getRequestURI() + "<BR>\n" +
"<B>Request Protocol: </B>" +
request.getProtocol() + "<BR><BR>\n" +
"<TABLE BORDER=1 ALIGN=\"CENTER\">\n" +
"<TR BGCOLOR=\"#FFAD00\">\n" +
"<TH>Header Name<TH>Header Value");
13
Basic Internet Programming
Servlets
...
Enumeration headerNames = request.getHeaderNames();
while(headerNames.hasMoreElements()) {
String headerName = (String)headerNames.nextElement();
out.println("<TR><TD>" + headerName);
out.println("
<TD>" + request.getHeader(headerName));
}
out.println("</TABLE>\n</BODY></HTML>");
}
/** Vi låter doPost använda doGet. */
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
Basic Internet Programming
Servlets
Cookies
Cookies
Š Cookies kan användas för att koppla data till viss
användare
„
Namn/lösen (försiktighet krävs dock!), var man varit på
siten, varukorg eller liknande
Š En cookie lagras på klientens dator
Š Vi nästa ansluten till servern kan man läsa av
cookien hos servern
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Basic Internet Programming
Servlets
... Exempel, setCookies
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);
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);
}
Basic Internet Programming
Servlets
...
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" +
"To see them, visit the\n" +
"<A HREF=\"/servlet/ShowCookies\">\n" +
"<CODE>ShowCookies</CODE> servlet</A>.\n" +
"<P>\n" +
"Three of the cookies are associated only with the\n" +
"current session, while three are persistent.\n" +
"Quit the browser, restart, and return to the\n" +
"<CODE>ShowCookies</CODE> servlet to verify that\n" +
"the three long-lived ones persist across sessions.\n" +
"</BODY></HTML>");
}}
15
Basic Internet Programming
Servlets
... Exempel, showCookies
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");
Basic Internet Programming
Servlets
...
Cookie[] cookies = request.getCookies();
if (cookies != null) {
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>");
}
}
16
Basic Internet Programming
Servlets
Sessionstracking
Sessionstracking
Š För att hantera en användares sessioner med en
server och kanske flytta data mellan olika delar kan
vi använda
„
Cookies
z
„
URL-rewriting
z
„
Kan vara avstängda hos klienten
Lite klumpigt att hantera
Hidden forms
z
Också lite knöligt
Š Java servlets erbjuder speciella sessionmekanismer
som döljer den faktiska metod som används
Basic Internet Programming
Servlets
exempel
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.net.*;
import java.util.*;
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;
Integer accessCount =
(Integer)session.getAttribute("accessCount");
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Basic Internet Programming
Servlets
...
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.setAttribute("accessCount", accessCount);
Basic Internet Programming
Servlets
...
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>" +
18
Basic Internet Programming
Servlets
...
new Date(session.getLastAccessedTime()) + "\n"
+
"<TR>\n" +
" <TD>Number of Previous Accesses\n" +
" <TD>" + accessCount + "\n" +
"</TABLE>\n" +
"</BODY></HTML>");
}
/** Handle GET and POST requests identically. */
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
Basic Internet Programming
Servlets
Request and Session Attributes
„
„
„
„
„
Servlet can access attributes stored within the request or
within the session
Attributes are like variables: One servlet can set an
attribute in the request or session, another (included or
forwarded to) servlet can retrieve the attribute value,
change it, etc
If the attribute is in the session, future accesses from the
same browser can read its value (this is how login is
done)
javax.servlet.ServletRequest.setAttribute(String name,
Object value), getAttribute(String name)
javax.servlet.HttpSession.setAttribute(String name,
Object value), getAttribute(String name)
19
Basic Internet Programming
Servlets
Hands-on with Tomcat
„
Various ways of mapping a servlet in web.xml
z
z
z
z
„
„
„
„
„
/servlet/HelloWorldServlet
/servlet/hello
/world
/anything.abc
A form response
Some HTTP request headers
Some HTTP response headers
Redirections, forwards, includes
Sessions
Basic Internet Programming
Servlets
Länkar
Tutorial från SUN
http://java.sun.com/docs/books/tutorial/servlets/index.html
Tutorial av Marty Hall
http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/
Diverse resurser
http://www.corewebprogramming.com/
20