Vad är JSP?
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Basic Internet Programming 2004
Java Server Pages (JSP)
Webapp filters
Cristian Bogdan
cristi@nada.kth.se
Björn Eiderbäck
bjorne@nada.kth.se
JSP: Pragmatisk exempelorienterad beskrivning
Webapp Filters
JSP taglibs
Basic Internet Programming
JSP and Webapp Filters
Vad är JSP?
En blandning av Java och XHTML/HTML
Man kan skriva stora delar av websidorna med HTML
och skriva script i Java och/eller inkludera Java-kod
Den som inte kan Java kan enklare delta och konstruera
stora delar av sidorna
Servlet containers generate servlets out of the JSP pages,
which contain request.getWriter().print(…) for every
HTML string in the page
Since JSP pages are servlets as well, they have all the
servlet functionality
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Basic Internet Programming
JSP and Webapp Filters
Exempel
<%@page language="java" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD><TITLE>Welcome!</TITLE></HEAD>
<BODY>
You are connecting from <% out.println(request.getRemoteHost()); %> <BR>
<TABLE border=1>
<%for(java.util.Enumeration e=request.getHeaderNames(); e.hasMoreElements(); ) {
%>
<% String headerName= (String)e.nextElement(); %>
<TR><TD><%=headerName %> <TD><%= request.getHeader(headerName)%>
<% } %>
</TABLE>
</BODY>
</HTML>
Basic Internet Programming
JSP and Webapp Filters
Fördelar med JSP jämfört med
andra tekniker
Jämfört med ASP
Java är kraftfullara än Basic och mer portabelt
Jämfört med PHP
Java mer vidspritt och kraftfullare språk, dvs Java
Jämfört med rena servlets
JSP översätts till servlet men det kan vara smidigare och enklare att
skriva mer HTML-lika beskrivningar för websidor. För mer
programmeringsintensiva delar passar servletar bättre
Jämfört med Server Side Includes (SSI)
SSI spritt men JSP har en rikare flora av verktyg
Jämfört med JavaScript
Java kraftfullare, enklare att skriva modulärt osv
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Basic Internet Programming
JSP and Webapp Filters
Fördefinierade variabler
pageContext
request
response
session
out
Exempel
z
z
javax.servlet.jsp.PageContext
javax.servlet.http.HttpServletRequest
javax.servlet.http. HttpServletResponse
javax.servlet.http.HttpSession
javax.servlet.jsp.JspWriter
<%= request.getRemoteHost() %>
<%= pageContext.getRequest().getRemoteHost() %>
Basic Internet Programming
JSP and Webapp Filters
JSP:s
JSP:s element
element
Siddirektiv <%@ page… import= … contentType=..%>
Kommentar <%-- Kommentar --%>
Scriplet <% Javakod %>
Utmatning <%= ... %>
Lite vanlig HTML blandad med Java <I>
<%= request.getParameter("title") %></I>
Kan också skrivas
<% out.print("Lite vanlig HTML blandad med Java
<I>");
out.print(request.getParameter("title") ;
out.println("</I>");
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Basic Internet Programming
JSP and Webapp Filters
Deklarationer
Class-level declarations, outside the service()
method <%! Javakod %>
Skrivs mellan <%! Javakod %>
<%! private int accessCount = 0; %>
Accesses to page since server reboot:
<%= ++accessCount %>
Basic Internet Programming
JSP and Webapp Filters
Other JSP issues
Det går alternativt att använda XML-taggar
istället
En JSP översätts till servlet och kompileras till en
servlet första gången den anropas
I denna version av Tomcat hamnar servlet och
kompilerad kod i
$CATALINA_HOME/work/localhost
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Basic Internet Programming
JSP and Webapp Filters
Page context attributes
Attributes visible only within the page (one request
can include more pages via
RequestDispatcher.include() or forward())
PageContext.setAttribute(String name, Object
value, int scope)
scope can be PageContext.PAGE_SCOPE (default),
PageContext.REQUEST_SCOPE (request attrs),
PageContext.SESSION_SCOPE (session attrs),
PageContext.APPLICATION_SCOPE (accessible to all
servlets and JSPs within the same webapp)
PageContext.getAttribute(String name, int scope)
Basic Internet Programming
JSP and Webapp Filters
Att
Att använda
använda bönor
bönor (eng
(eng Beans)
Beans)
och
och JSP
JSP
Med Java-bönor kan vi inkludera, läsa och
uppdatera vanliga klasser
Se
http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/Servlet-TutorialJSP.html#Section8
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Basic Internet Programming
JSP and Webapp Filters
Ett exempel
<%@ page import = "num.NumberGuessBean" %>
<jsp:useBean id="numguess"
class="num.NumberGuessBean" scope="session"/>
<jsp:setProperty name="numguess" property="*"/>
<html>
<head><title>Number Guess</title></head>
<body bgcolor="white">
<font size=4>
Basic Internet Programming
JSP and Webapp Filters
...
<% if (numguess.getSuccess()) { %>
Congratulations! You got it.
And after just <%= numguess.getNumGuesses() %>
tries.<p>
<% numguess.reset(); %>
Care to <a href="numguess.jsp">try again</a>?
<% } else if (numguess.getNumGuesses() == 0) { %>
Welcome to the Number Guess game.<p>
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JSP and Webapp Filters
...
I'm thinking of a number between 1 and 100.<p>
<form method=get>
What's your guess? <input type=text name=guess>
<input type=submit value="Submit">
</form>
<% } else { %>
Good guess, but nope.
%></b>.
Try <b><%= numguess.getHint()
You have made <%= numguess.getNumGuesses() %>
guesses.<p>
Basic Internet Programming
JSP and Webapp Filters
...
I'm thinking of a number between 1 and 100.<p>
<form method=get>
What's your guess? <input type=text name=guess>
<input type=submit value="Submit">
</form>
<% } %>
</font>
</body>
</html>
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JSP and Webapp Filters
num.NumberGuessBean.java
package num;
import java.util.*;
public class NumberGuessBean {
int answer;
boolean success;
String hint;
int numGuesses;
public NumberGuessBean() {
reset();
}
Basic Internet Programming
JSP and Webapp Filters
...
public void setGuess(String guess) {
numGuesses++;
int g;
try {
g = Integer.parseInt(guess);
}
catch (NumberFormatException e) {
g = -1;
}
if (g == answer) {
success = true;
}
else if (g == -1) {
hint = "a number next time";
}
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JSP and Webapp Filters
...
else if (g < answer) {
hint = "higher";
}
else if (g > answer) {
hint = "lower";
}
}
public boolean getSuccess() {
return success;
}
public String getHint() {
return "" + hint;
}
Basic Internet Programming
JSP and Webapp Filters
...
public int getNumGuesses() {
return numGuesses;
}
public void reset() {
answer = Math.abs(new Random().nextInt() % 100) + 1;
success = false;
numGuesses = 0;
}
}
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JSP and Webapp Filters
Fler exempel
Vi tittar lite snabbt på exemplen i Tomcat
Basic Internet Programming
JSP and Webapp Filters
Integrera
Integrera Servlets
Servlets och
och JSP
JSP
Man kan integrera Servlet och JSP med
varandra
Den ena kan skicka data till den andra genom
att tex utöka och skicka vidare innehållet i
requestvariabeln, använda sessionsvariabler
mm
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Basic Internet Programming
JSP and Webapp Filters
Servlet-JSP: Skicka vidare
”request”
I Servlet definiera URL för JSP-sida
String url = ”/katalog/sida.jsp”;
Skicka vidare kontroll till JSP-sidan
RequestDispatcher dispatcher =
getServletContext().getRequestDispatcher(url);
dispatcher.forward(request, response);
In this scenario, the servlet decides which
JSP to invoke, depending on its internal logic
Basic Internet Programming
JSP and Webapp Filters
Servlet-JSP:communication via
attributes
Använd någon av
Servlet
SomeClass value = new SomeClass(...);
request.setAttribute(”key”, value);
JSP
<jsp:useBean id=”key” class=”SomeClass” scope=”request” />
Servlet
HttpSession session = request.getSession(true);
session.setAttribute(”key”, value);
JSP
<jsp:useBean id=”key” class=”SomeClass” scope=”session” />
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Basic Internet Programming
JSP and Webapp Filters
Communication via Web
application-level attributes
Servlet
getServletContext().setAttribute(”key”, value);
JSP
<jsp:useBean id=”key” class=”SomeClass”
scope=”application” />
Basic Internet Programming
JSP and Webapp Filters
Custom JSP tag libraries
<%@ taglib uri="http://www.taglibprovider.com/name" prefix=”special" %>
<HTML>…
<special:makeBold>this text will become bold</special:makeBold>
<special:timeOfDay format=”hh:MM:ss” />
</HTML>
javax.servlet.jsp.tagext.*, Tag, BodyTag…
Tag library descriptor (TLD): info on each tag and params
Install the tag library in your web.xml
<taglib>
<taglib-uri>http://jakarta.apache.org/taglibs/mailer-1.0</taglib-uri>
<taglib-location>/WEB-INF/mailer.tld</taglib-location>
</taglib>
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Basic Internet Programming
JSP and Webapp Filters
Standard Tag Library (JSTL)
Problem: hard to program taglibs when the JSP
author can use Java scriplets near the custom tags
Simple programming within the page (instead of
Java)
<c:forEach items="${orders}" var="order">
<c:out value="${order.id}"/>
</c:forEach>
The expression language (EL) ${order.id+order1.id2}
EL supported in soon-to-come JSP 2.0, phasing out
Java <%scriplets %>
Basic Internet Programming
JSP and Webapp Filters
Filters
Using a servlet to dispatch JSPs or other servlets
(by forwarding the ”request”) centralizes all
accesses to that servlet. All forms will have to be
submitted to that servlet as ”action”, which looks
ugly in the browser
Filters are similar with operating system filters:
program1 | program2 | program3
filter1| filter2| filter3 | contentGenerator
contentGenerator can be a servlet, JSP or simple
HTML
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Basic Internet Programming
JSP and Webapp Filters
…
Servlets could do content filtering with include()
but filters are more standard and more powerful
filters just need to be configured in web.xml to take
effect, with servlets you would have to change Java
code
filters can alter the request and the response (using
wrappers) and the generated content
Controller filters (MVC), authentication filters,
Logging filters, etc.
Basic Internet Programming
JSP and Webapp Filters
Filter basics, wrappers
A basic filter
public class MyFilter implements javax.servlet.Filter{
public void init(javax.servlet.FilterConfig c) {… }
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain)throws ServletException, java.io.IOException
{ … chain.doFilter(req, resp); …} // invoke the filter chain
public void destroy(){}
}
We can pass ”wrapped” request and response to doFilter()
class MyRequest extends HttpServletRequestWrapper {
MyRequest(HttpServletRequest req) { super(req); }
public String getRemoteUser(){return getRequest().getRemoteUser()+”a”;}
public String getQueryString() { … }
} // we can redefine any other ServletRequest method!
Easier to define wrappers as anonymous inner classes
ServletRequest req1= new HttpServletRequestWrapper(req){
public String getRemoteUser(){ }… public String getQueryString(){ }…
};
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Basic Internet Programming
JSP and Webapp Filters
Länkar
Tutorial från SUN
http://java.sun.com/products/jsp/
JSP 2.0:
http://jcp.org/aboutJava/communityprocess/first/jsr152/
Standard tag library
http://java.sun.com/products/jsp/jstl/
http://jakarta.apache.org/taglibs
Tutorial av Marty Hall
http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/
http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/ServletTutorial-JSP.html
Diverse resurser
http://www.corewebprogramming.com/
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