JavaServer Pages Fundamentals
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JavaServer Pages
Fundamentals
Prof. Dr.-Ing. Thomas Korte
Laboratory of Information Technology
1
Montag, 4. Mai 2009
Introduction to JSP
• JavaServer
Pages
(JSP)
is
a
Java
technology
which
enables
the
development
of
dynamic
web
sites.
– JSP was developed by Sun Microsystems to allow server side
development.
– JSP files are HTML files with special Tags containing Java source
code that provide the dynamic content.
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
2
Why Should I Use JSP?
• JSP
is
easy
to
learn
and
allows
developers
to
quickly
produce
web
sites
and
applica@ons
in
an
open
and
standard
way.
– main advantages of JSP:
• multi-platform, i.e. JSPs can be moved to different platforms
• uses Java and is therefor not locked to qspecific vendor
• provides a separation between presentation (HTML) and
implementation (Java) code
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
3
JSP Compared to Other Technologies
• JSP
compared
to
ASP
or
ASP.NET
– Microsofts Active Server Pages
• similar functionality
• both allow embedded code in HTML pages, session variables and
database access
• ASP is bound to Microsoft
• ASP.NET supports application development using different languages
such as Visual Basic, C# and JavaScript
• JSP
compared
to
Servlets
– A Servlet is a Java class that provides special server side service.
It is hard work to write HTML code in Servlets.
– In Servlets you need to have lots of println statements to generate
HTML.
– JSP pages are converted to Servlets so actually can do the same
thing as old Java Servlets.
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
4
JSP Architecture
• JSPs
are
built
on
top
of
the
servlet
technology.
– JSPs are essential an HTML page with special JSP tags
embedded.
• These JSP tags can contain Java code.
• The JSP file extension is .jsp rather than .htm or .html.
• The JSP engine parses the .jsp and creates a Java servlet source file. It
then compiles the source file into a class file, this is done the first time
and this why the JSP is probably slower the first time it is accessed. Any
time after this the special compiled servlet is executed and is
therefore returns faster.
– The figure on the next page depicts a JSP request from a web
browser.
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
5
Requesting a JSP Page
3.The Web server recognises the file
from its .jsp extension and passes it
to the JSP Servlet Engine.
– If the JSP file has not been called
the first time, step 7 is performed.
4.If the JSP file has been called the
first time, servlet source code is
generated from the JSP file.
5.All the HTML text is converted to
println statements.
6.The servlet source code is compiled
into a class.
7.The Servlet is instantiated,calling the
init and service methods.
8.HTML from the Servlet output is sent
via the Internet.
9.HTML results are displayed on the
user's web browser.
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
6
Setting up a JSP Environment
• get
a
Java
SE
JDK
• download
the
JSP
environement
– http://java.sun.com/products/jsp/index.jsp
• download
a
web
server
and
a
JSP
and
Servlet
engine
– A much used option is to download the Tomcat server.
– In Tomcat, a free open source Web server is combined with a
JSP and Servlet engine, developed by the Apache foundation.
– http://tomcat.apache.org
» alternatively download the NetBeans IDE, which
contains Web/applications servers and the JSP and
servlet libraries.
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
7
Creating Your first JSP Page
• Type
the
code
below
into
a
text
file
index.jsp
and
place
it
in
the
correct
directory
into
your
JSP
web
server
instala@on.
– Then call it via your browser.
<html>
<head>
<title>My first JSP page
</title>
</head>
<body>
<%@ page language="java" %>
<% out.println("Hello World"); %>
</body>
</html>
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
8
Using JSP Tags
• There
are
five
main
tags:
–
–
–
–
–
Declaration tag
Expression tag
Directive tag
Scriptlet tag
Action tag
• Declara@on
Tag
(
<%!
%>
)
– This tag allows the developer to declare variables or methods.
– Before the declaration you must have <%!
– At the end of the declaration,the developer must have %>
– Code placed in this tag must end in a semicolon ( ; ).
– Declarations do not generate output so are used with JSP expressions or
scriptlets. For Example:
<%!
private int counter = 0 ;
private String get Account ( int accountNo) ;
%>
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
9
Expression Tag
• Expression
tag
(
<%=
%>)
– This tag allows the developer to embed any Java expression and
is short for out.println().
– A semicolon ( ; ) does not appear at the end of the code inside
the tag.
– For example,to show the current date and time:
Date : <%= new java.util.Date() %>
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
10
Directive Tag
• direc@ve
tag
(
<%@
direc@ve
...
%>
)
– A JSP directive gives special information about the page to the
JSP Engine. There are three main types of directives: 1) page - processing information for this page.
2) Include - files to be included.
3) Tag library - tag library to be used in this page. – Directives do not produce any visible output when the page is
requested but change the way the JSP Engine processes the
page.
– For example,you can make session data unavailable to a page
by setting a page directive (session) to false.
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
11
Sciptlet Tag
• scriptlet
tag
(
<%
...
%>
)
– Between <% and %> tags, any valid Java code is called a
Scriptlet.
– This code can access any variable or bean declared.
– For example, to print a variable: <% String username = "visualbuilder" ;
out.println ( username ) ;
%>
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
12
Action Tag
• There
are
three
main
roles
of
ac@on
tags:
1. enable the use of server side Javabeans
2. transfer control between pages
3. browser independent support for applets.
• A Javabean is a special type of class that has a number of specially
named methods.
• The JSP page can call these methods so almost all Java code in JSPs
can be hidden in Javabeans. • To
use
a
Javabean
in
a
JSP
page
use
the
following
syntax:
• <jsp : usebean id = " ...." scope = "application" class = "com..." />
• The following is a list of Javabean scopes:
–
–
–
–
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
page - valid until page completes.
request - bean instance lasts for the client request
session - bean lasts for the client session.
application - bean instance created and lasts until application ends. 13
Creating Your Second JSP Page
• crea@ng
a
page
visit
counter
<HTML>
<HEAD>
<TITLE>Using the Application Object</TITLE>
</HEAD>
<BODY>
<H1>Using the Application Object</H1>
<%
Integer counter = (Integer)session.getAttribute("counter");
String heading = null;
if (counter == null) {
counter = new Integer(1);
} else {
counter = new Integer(counter.intValue() + 1);
}
session.setAttribute("counter", counter);
Integer applicationCounter = (Integer)application.getAttribute("applicationCounter");
if (applicationCounter == null) {
applicationCounter = new Integer(1);
} else {
applicationCounter = new Integer(applicationCounter.intValue() + 1);
}
application.setAttribute("applicationCounter", applicationCounter);
%>
You have visited this page <%=counter%> times.
<BR>
This page has been visited by all users <%=applicationCounter%> times.
</BODY>
</HTML>
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
14
Implicit Objects
– The Servlet creates several implicit objects a JSP can access:
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
15
The Implicit Object out
• out
object
example:
outexample.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<%
for(int i=0;i<10;i++){
for(int j=0;j<=i;j++){
out.print("*");
}
out.println("<br>");
}
%>
</body>
</html>
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
16
The Implicit Objects request, response
• request
object
The request object is created for each request and once the response is
submitted then it gets destroyed. The request object is used to pass the
information from one page to the other page if the pages are getting invoked
during the request lifecycle.
• response
object
The response object is used to send and set the information at the client side.
The cookies are the small files used to save the information in the client machine
which can be used for some further actions and state maintenance.
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
17
The Implicit Object session
• session
object
example
The session object is an instance of HttpSession and is used to track information
about a particular client.
Each client has one global session object.
When a user sends the fist request to the JSP engine, it will issue a session id to
track the information for the transaction.
The below example will show the session id as well as the count which shows how
many times the page is accessed during the current session.
sessionexample.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
Sesion id for the Session is :- <%=session.getId() %><br>
<%
if (session.getAttribute("count") != null){
int count = Integer.parseInt((String)session.getAttribute("count"));
count++;
out.println("The number of times the page accessed " + count );
session.setAttribute("count",String.valueOf(count));
}else{
session.setAttribute("count","1");
out.println("The page is accessed for the first time");
}
%>
</body></html>
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
18
The Implicit Object application
• applica@on
object
•
Unlike session object which are created separately for each client browser, one
application object is created for whole application.
•
This object remains in the memory once the application is initialized.
•
It is destroyed when the application will be removed from the server or the
server shuts down.
•
This is a static object which is shared by all the clients.
•
The application object is normally used to cache data for better performance.
•
The page counter example from a previous page uses the application object.
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
19
Working with HTML forms
• The
basic
form
control
aQributes:
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
20
A HTML Form Example
• username/password
request
form
(login.html)
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Language" content="en-us">
<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
<title>Login Form</title>
</head>
<body>
<p align="left"><b>Login Form
</b></p>
<form name="loginForm" >
no
ac@on
is
associated
with
this
form
<table border="1" width="50%" cellspacing="1" cellpadding="0" id="table1">
<tr>
<td width="50%">&nbsp;Login Name</td>
<td><input type="text" name="loginName" size="20"></td>
</tr>
<tr>
<td width="50%">Password</td>
<td><input type="password" name="password" size="20"></td>
</tr>
</table>
<p><input type="submit" value="Submit" name="B1"><input type="reset" value="Reset" name="B2"></p>
</form>
</body>
</html>
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
21
How to Get Data From a Form
• How
do
we
get
the
form
data
into
a
JSP‐Page?
– We need to first define which JSP page should be accessed
when this form is submitted.
• This can be achieved by the action attribute in the <form>.
• For example: <form action="login.jsp"> will generate a request for
the login.jsp page when the submit button will be clicked for the form.
– We then need to create the file login.jsp to show the data which
the user has sent from the login.html page from the previous
example.
– Example login.jsp file: (next page)
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
22
A HTML Form Example With JSP-Processing
• username/password
request
form
(Login.html)
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Language" content="en-us">
<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
<title>Login Form</title>
</head>
<body>
<p align="left"><b>Login Form
</b></p>
<form name="loginForm" method = "POST" action = "login.jsp" >
now
the
ac@on
is
to
call
up
login.jsp
<table border="1" width="50%" cellspacing="1" cellpadding="0" id="table1">
<tr>
<td width="50%">&nbsp;Login Name</td>
<td><input type="text" name="loginName" size="20"></td>
</tr>
<tr>
<td width="50%">Password</td>
<td><input type="password" name="password" size="20"></td>
</tr>
</table>
<p><input type="submit" value="Submit" name="B1"><input type="reset" value="Reset" name="B2"></p>
</form>
</body>
</html>
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
23
The login.jsp Page to Process The Form
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/
TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Login Form Data</title>
</head>
<body>
<b>Submitted Values are </b>
<table border="1" width="50%" cellspacing="1" cellpadding="0" id="table1">
<tr>
<td width="50%">&nbsp;Login Name</td>
<td><%=request.getParameter("loginName") %></td>
</tr>
<tr>
<td width="50%">Password</td>
<td><%=request.getParameter("password") %></td>
</tr>
</table>
</body>
</html>
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
24
HTML Form Validation
• form
valida@on
– Form validation is the process of checking that a form has been filled in
correctly before it is processed.
– There are mainly two types of form validations: server-side (using JSP ASP,
etc), and client-side (usually done using JavaScript). The difference is:
• Client side validation runs in the browser to check that the form values
are of the correct type. It should be done using JavaScript (VBScript is
supported only by IE).
• Server side validation checks the code that is submitted to make sure it
is correct.
– The following example will show how to use JavaScript to validate the login
form:
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
25
HTMl form validation using JavaScript
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01
Transitional//EN" "http://www.w3.org/TR/html4/
loose.dtd">
<html><head><meta http-equiv="ContentLanguage" content="en-us">
<meta http-equiv="Content-Type" content="text/
html; charset=windows-1252">
<title>Registration Form</title>
</head><script>
function validateForm(form){
if(form.firstName.value==''){
alert ("First Name can not be blank");
return false;
}
if(form.lastName.value==''){
alert ("Last Name can not be blank");
return false;
}
if(form.introduction.value==''){
alert ("Introduce Yourself can not be
blank");
return false;
}
if(form.phone.value==''){
alert ("Phone can not be blank");
return false;
}
if(form.address.value==''){
alert ("Address can not be blank");
return false;
}
if(form.city.value==''){
alert ("City can not be blank");
return false;
}
if(form.state.value==''){
alert ("State can not be blank");
return false;
}
}
</script><body>
04/18/09 - Prof. Dr.-Ing. Thomas Korte
<p align="left"><b>Registration Form</b></p>
Montag, 4. Mai 2009
<form name="registerationForm" method="POST"
action="processRegistration.jsp" onsubmit="return
validateForm(document.registerationForm); ">
<table border="1" width="70%" cellspacing="1"
cellpadding="0" id="table1">
<tr><td width="50%">First Name</td>
<td><input type="text" name="firstName"
size="20"></td>
</tr><tr>
<td width="50%">Last Name</td>
<td><input type="text" name="lastName"
size="20"></td>
</tr><tr>
<td width="50%">Introduce Yourself</td>
<td><textarea name="introduction" cols="40"
rows="10"></textarea></td>
</tr><tr>
<td width="50%">Gender</td>
<td><input type="radio" value="V1" checked
name="radio1">male
<input type="radio" name="radio1"
value="V2">female</td>
</tr><tr>
<td width="50%">Phone</td>
<td><input type="text" name="phone" size="20"></
td></tr><tr>
...
<td width="50%">State</td>
<td><input type="text" name="state" size="20"></td>
</tr><tr>
<td width="50%">Country</td>
<td><select size="1" name="country">
<option selected value="United Kingdom">United
Kingdom</option>
<option>USA</option>
<option>Other</option>
</select></td>
</tr></table>
<p><input type="submit" value="Submit"
name="B1"><input type="reset" value="Reset"
name="B2"></p>
</form></body></html>
26
Layout of The Form
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
27
The Same Validation using a JSP page…
• validateRegistra@onWithJSP.jsp
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Language" content="en-us">
<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
<title>Registration Form</title>
</head>
<body>
<p align="left"><b>Registration Form</b></p>
<form name="registerationForm" method="POST" action="validateRegistrationWithJSP.jsp">
<table border="1" width="70%" cellspacing="1" cellpadding="0" id="table1">
<%
String errors=(String)request.getAttribute("errors");
if(errors != null && errors.trim().length()>0){
out.println("<tr><td colspan='2'>The following are the errors with given data<br>"+errors+"</td></tr>");
}
%>
<tr>
<td width="50%">First Name</td>
<td><input type="text" name="loginName" size="20" value="<%=request.getParameter("loginName")!=null?request.getParameter("loginName"):""%>"></
td></tr>
<tr>
<td width="50%">Last Name</td>
<td><input type="text" name="password" size="20" value="<%=request.getParameter("password")!=null?request.getParameter("password"):""%>"></
td></tr>
<tr>
<td width="50%">Introduce Yourself</td>
<td><textarea name="intro" cols="40" rows="10"><%=request.getParameter("intro")!=null?request.getParameter("intro"):""%></textarea></td>
</tr>
<tr>
<td width="50%">Gender</td>
<td>…
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
28
Bildschirmausgabe nach Fehlern
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Montag, 4. Mai 2009
29
Die Seite validateRegistrationWithJSP.jsp
<%@ page language="java" contentType="text/html;
charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//
EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;
charset=ISO-8859-1">
</head>
<body>
<%
String loginName=request.getParameter("loginName");
String password=request.getParameter("password");
String intro=request.getParameter("intro");
String gender=request.getParameter("R1");
String phone=request.getParameter("phone");
String address=request.getParameter("address");
String city=request.getParameter("city");
String state=request.getParameter("state");
String country=request.getParameter("country");
String errors="";
if(loginName ==null || loginName.trim().length() ==0){
errors=errors+"<li>Please enter the Login Name<br>";
}
if(password ==null || password.trim().length() ==0){
errors=errors+"<li>Please enter the Password<br>";
}
if(intro ==null || intro.trim().length() ==0){
errors=errors+"<li>Please enter the introduction<br>";
}
if(gender ==null || gender.trim().length() ==0){
errors=errors+"<li>Please select Gender<br>";
}
if(phone ==null || phone.trim().length() ==0){
}
if(address ==null || address.trim().length() ==0){
errors=errors+"<li>Please enter address<br>";
}
if(city ==null || city.trim().length() ==0){
errors=errors+"<li>Please enter city<br>";
}
if(state ==null || state.trim().length() ==0){
errors=errors+"<li>Please enter state<br>";
}
if(country ==null || country.trim().length() ==0){
errors=errors+"<li>Please enter country<br>";
}
if( errors.trim().length() >0){
request.setAttribute("errors",errors);
%>
<jsp:forward page="registerwithvalidation.jsp"></
jsp:forward>
<%
}
%>
<h1>The given data is Valid.</h1>
</body>
</html>
errors=errors+"<li>Please enter phone<br>";
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
30
Concentrating JSP Java-Code into Beans
• For
beQer
readability
of
JSP‐pages,
the
embedded
Java
code
may
be
moved
into
the
Java
Beans
– Java Beans are normal Java classes, which use a naming
convention to allow for easy introspection and reflection.
– JSP use special tags to set and get the data from a Java Beans.
– The same example using a Bean:
• validateRegistra@onWithBean.jsp
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Language" content="en-us">
<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
<title>Registration Form</title>
</head>
<body>
<p align="left"><b>Registration Form</b></p>
<form name="registerationForm" method="POST" action="validateRegistrationWithBean.jsp">
<table border="1" width="70%" cellspacing="1" cellpadding="0" id="table1">
<%
String errors=(String)request.getAttribute("errors");
if(errors != null && errors.trim().length()>0){
out.println("<tr><td colspan='2'>The following are the errors with given data<br>"+errors+"</
td></tr>");
}...
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Montag, 4. Mai 2009
31
Die Seite validateRegistrationWithBean.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://
www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
</head>
<body>
<jsp:useBean id="bean" class="com.visualbuilder.beans.RegistrationBean"/>
<jsp:setProperty name="bean" property="*"/>
<%
com.visualbuilder.beans.RegistrationBean
register=(com.visualbuilder.beans.RegistrationBean)pageContext.getAttribute("bean");
register.validate(request);
String errors= (String)request.getAttribute("errors");
if( errors.trim().length() >0){
%>
<jsp:forward page="registerwithbean.jsp"></jsp:forward>
<%
}
%>
<h1>The given data is Valid.</h1>
</body>
</html>
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
32
Die Java Bean RegistrationBean.java
• package com.visualbuilder.beans;
import javax.servlet.http.HttpServletRequest;
public class RegistrationBean {
String loginName, password, intro, gender, phone, address, city, state, country;
public String getLoginName() {
return loginName;
}
public void setLoginName(String loginName) {
this.loginName = loginName;
}
public String getPassword() {
...
public void validate(HttpServletRequest request){
String errors="";
if(loginName ==null || loginName.trim().length() ==0){
errors=errors+"<li>Please enter the Login Name<br>";
}
if(password ==null || password.trim().length() ==0){
...
}
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
33
Further Reading
• jGuru:
Introduc.on
to
JavaServer
Pages
technology
– http://java.sun.com/developer/onlineTraining/JSPIntro/index.html
• Servlet
and
JavaServer
Pages
technology
free
online
books
– http://books.coreservlets.com/
especially read Chapter 3 of this book
• A Fast Introduction to Basic JSP Programming
– http://pdf.moreservlets.com/More-Servlets-and-JSP-Chapter-03.pdf
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
34
What is a Web Application?
• A
client/server
applica@on
using
a
collec@on
of
web
components
on
the
server,
which
are:
–
–
–
–
–
servlets,
JavaServer Pages,
tag libraries,
Web services,
JavaBeans.
• examples:
– electronic shopping mall
– auction site
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
35
Request and Response in a Web Application
• browser
sends
requests
to
web
server
servlet container translates
JSPs into servlets in order to
run them in a web server
• web
server
passes
request
to
a
web
applica@on
• web
applica@on
runs
inside
a
servlet
container
• web
applica@on
generates
a
response
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
FIGURE 1-1
Requests and Responses in a Web Application
Web applications consist of a varied set of interrelated web components. This set
includes JSP pages, servlets, and tag libraries that work together. Resources utilized
within the web application must be coordinated using a deployment descriptor file.
This file contains the meta-information that describes the web application. The
servlet container translates JSP files into servlets in order to run them in the web
server. Chapter 2 provides more detailed explanations of the components in this
illustration.
deployment descriptor (XML file)
describes the components
(resources) of the web application
Challenges in Developing Web
Applications
Two key characteristics distinguish web applications from standalone applications:
36
Web Application Characteristics
• In
contrast
to
standalone
applica@ons,
web
applica@on
components
do
not
interact
directly,
but
via
a
servlet
container
and
a
web
browser.
– servlet container: web server extension to excute Java code of
web components
• Data
representa@on,
flow,
and
processing
are
distributed
among
– the client browser,
– the servlet container,
– and individual web components
• Informa@on
storage
and
database
access
take
place
in
the
server.
– The application resides on the server.
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
37
Web Application Development is Different…
• Web
components
communicate
with
one
another
through
the
servlet
container.
• Data
is
always
passed
as
strings
• An
applica@on
consists
of
coopera@ng
processes.
• Tes@ng
must
take
place
on
mul@ple
browsers
and
servers.
• Debugging
is
difficult!
• The
deployment
of
a
Web
applica@on
is
typically
a
@me
consuming
task.
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
38
How IDEs can Help
• IDES
help
with:
– editors for JSP Pages, servlets, tag libraries
– syntax coloring, code checking, code completion, compilation,
UML diagrams
– wizards for the generation of web service components
– generation of the deployment descriptor
• deployment descriptor:
– xml-file that describes the components of a web application
–
–
–
–
deployment with a web module structure
execution support
source level debugging of JSPs, servlets and helper classes
http requests and responses can be captured
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
39
The Structure of Web Applications
• The
server
side
elements
of
a
web
applica@on
are
called
a
web
module.
– A web module contains the web components.
– A web module runs inside a servlet container.
• A servlet container is contained within a web server.
– The contents of a web module:
• presentation elements
– define views = pages the users see and interact with
» HTML files and/or JSP pages
• controller element
– controls page flow, filters in/output
» a servlet
• model
– the application logic and resources
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
40
Web Server
• A
Web
server
provides
mechanisms
for
clients
to
access
resources
on
a
server.
– The mechanisms include
• support for http and other protocols
• execution of server side programms
• support for servlet container
• Servlet
Container
–
–
–
–
–
offer services for the web components of a web module
life-cycle management
network services for requests and responses
decoding of requests and formatting of responses
interpretation and processing of JSP pages into servlets
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
41
Web Modules
• A
Web
module
is
a
deployable
unit
consis@ng
of
web
components
and
sta@c
content
files
(e.g.
images,
HTML
files).
– It resides in a root directory.
– It contains a standard layout of subfolders.
– It contains a deployment descriptor:
• web.xml file
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
42
JavaServer Faces
• A
Server‐Side
User
Interface
Component
Framework
– based on the JSP technology
further reading:
• http://www.coreservlets.com/JSF-Tutorial/
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
43
Web Applications With a Browser Interface
• JSF
is
a
liQle
more
elaborate
than
JSP.
– The user interface runs on the server.
– It is using a set of UI components a browser is able to render.
– Special: Java UI components are mapped to special HTML tags.
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
44
JSF Architecture
• JavaServer
Faces
technology
components:
– API representing UI components:
•
•
•
•
•
state management,
event handling,
validation,
data conversion,
page navigation
– two JavaServerPages custom tag libraries
• map components to server-side java objects
!"#$%&&
!"#$()*+
!"4$-5/.$1($*2+'(3
!"#$%&&
!"#$%&'
41(+*'+$-5/63
"'()*'+,$-./0$1($*2+'(3
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
45
Benefits
• The
separa@on
of
programm
logic
(Java
code)
from
presenta@on
(HTML
code).
• Page
designers
and
java
programmers
can
focus
on
their
piece
of
the
development
process.
• There
is
a
component
specific
event
handling.
• UI
elements
are
stateful
objects
on
the
server.
• Model‐View‐Controller
Architecture
.(&/'(%9"#$%+1$(&
!"#$%&#''(&)
*+,(-.(&/'(%
!"#$%&'%()
5
()/
45
)%
)./
Montag, 4. Mai 2009
3" #
5&#2-(&
0"#$%1.2%-)
6"#$%(7,5(%
04/18/09 - Prof. Dr.-Ing. Thomas Korte
:;.
!01(2)
3.4
!6#7(')
6+$+8(795(+$
*"#+((,-./)%
46
A JavaServer Faces Application…
• runs
in
a
servlet
container
and
contains:
– JavaBeans components containing application-specific
functionality and data
– Event Listeners
– HTML pages written as JSP pages
– server-side helper classes, such as DB access beans
• has:
– a custom HTML tag library for rendering UI components on a
page
– a custom tag library for representing event handlers, validators,
and other actions
– UI components represented as stateful objects on the server
– an application configuration resource file
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
47
MVC Pattern
• The
model
contains
applica@on
data.
• The
view
is
a
JavaServer
page.
• The
controller
is
a
FacesServlet
– which receives the HTTP request
– which populates a form bean with values from request
parameters
– which validates the form bean using standard and user-written
validators, and redisplays the page if errror are found
– which dispatches to an Action to process the form
04/18/09 - Prof. Dr.-Ing. Thomas Korte
Montag, 4. Mai 2009
48
