© Copyright 2008 STI - INNSBRUCK www.sti-innsbruck.at
Web Engineering
Web Technologies II
Lecture X – 9th December 2008
Federico M. Facca

Web Engineering (703512)
Where are we?
# Date Title Lecturer
1 7th Oct Web Engineering Introduction and Overview F. M. Facca
2 14h Oct Collection Requirements for Web Applications F. M. Facca
3 21st Oct Web Application Modeling F. M. Facca
4 28th Oct Developing Applications with WebML F. M. Facca
5 4th Nov Web Application Architectures I F. M. Facca
6 11th Nov Web Application Architectures II F. M. Facca
7 18th Nov Testing and Usability on the Web F. M. Facca
8 25th Nov Mid Term Exam F. M. Facca
9 2nd Dec Web Technologies I F. M. Facca
10 9th Dec Web Technologies II F. M. Facca
11 16th Dec Web Technologies III F. M. Facca
12 13th Jan Web 2.0 Mash-ups F. Daniel (UNITN)
13 20th Jan Web Application Development Process/
Project Management for Web Applications
F. M. Facca
14 27th Jan Final Exam F. M. Facca
2

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Overview
• Servlet
• JSP
• Java Beans
• Wrap-up
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SERVLETS
4

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Servlet Overview
• Servlet is an extension to the web server that adds
additional functionalities and programmability
• Servlet makes full use of the Java platform
• A servlet is basically a Java class. Every servlet
extends “javax.servlet.http.HttpServlet” class
• Related classes are wrapped in the package of
“javax.servlet” and “javax.servlet.http”
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Java Servlet Web Application
• Servlet development life cycle
– Development
• Defining servlet classes, methods and properties
– Deployment
• Servlet mapping to web environment
• Deployment on Web Application Server
– Execution
• Understand its execution life cycle

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Basic Servlet Structure
public class HelloWorld extends HttpServlet
{
public void doGet(HttpServletRequest request,
HttpServletResponse response )
throws ServletException,
java.io.IOException
{ … }
public void doPost(HttpServletRequest request,
HttpServletResponse response )
throws ServletException, IOException
{ … }
}

Web Engineering (703512)
Constructor and “Main” Method
• Servlet instances are created (invoked) by servlet
container automatically when requested – not by
user classes or methods
– No need to define constructor
• The entry point is NOT the “main” method, but the
two methods
– Use “doGet” or “doPost” to perform tasks

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Servlet Deployment
• Web content root folder (public_html)
– The starting point of the whole web application
– All files and sub-directories goes here:
html, images, documents …
• /public_html/WEB-INF/
– This folder contains configuration files
and compiled class
– Not directly accessible through the web
• /public_html/WEB-INF/classes/
– All compiled classes (servlet classes and other classes)
are in this folder

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Servlet Mapping
• Servlet class needs to be mapped to an accessible
URI (mainly through HTTP)
• For convenience, a servlet can be accessed in a
general pattern (invoker servlet)
– http://[domain]/[context]/servlet/[ServletClassName]
– http://localhost:8988/servletintro/servlet/SimpleServlet
• Specific mapping: using the configuration file
“web.xml”
– A servlet is specifically mapped to a user defined URL
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“web.xml” Configuration
• Using the file
“web.xml” for more
specific mapping
– The file is in the
“WEB-INF” folder
• Example
– Servlet class
• HelloWorld.class
– Application context:
• http://localhost:8080/servletintro/
– Invoker class mapping
• http://localhost:8080/servletintro/servlet/HelloWorld
– Specific mapping
• http://localhost:8080/servletintro/hello
– For more mapping examples, see example “web.xml”
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<servlet>
<servlet-name>HelloW</servlet-name>
<servlet-class>HelloWorld
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>HelloW</servlet-name>
<url-pattern>hello</url-pattern>
</servlet-mapping>

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Servlet Execution Life Cycle
Servlet Class
Servlet Instance in Memory
init()
service()
doPost()
doGet()
First Request
Subsequent
Requests (can
be from
different users
and sessions)

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Response and Request Message
• Web servers and web clients communicate through
HTTP messages (protocols)
– Request message: client  server
– Response message: server  client
• HTTP message consists of header and body
– HTTP header: information describing the message and the
context of the message
– HTTP body: content usually for display
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Request Processing
• Major request method type
– Get
• User data is sent as part of the request URL
• No request message body
• Triggering actions: address bar (in browser), link, form, …
– Post
• User data is sent in the request message body
• Triggering actions: form, …
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doGet() Method
• Servlet class uses the “doGet()” method to process
general (servlet) URL request
public void doGet( HttpServletRequest request,
HttpServletResponse response )
throws ServletException,IOException
{
( generating response message … )
}
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Response Processing
• Response body
– Generating HTML or other content for display
• Response header
– Manipulating response message header data to affect its
behavior
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Generating Response Content
• Using “response”
(javax.servlet.http.HttpServletResponse) and
“java.io.PrintWriter” to generate HTML to the output
stream
java.io.PrintWriter out =
response.getWriter();
out.println(“<html>”);
…
out.println(“</html>”);
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Using StringBuffer
• When there are frequent changes to a string,
using StringBuffer (java.lang.StringBuffer) is more
efficient
StringBuffer html = new StringBuffer();
html.append(“<html>”);
html.append(“<head>");
…
…
String s= html.toString();
• This is very useful when generating HTML page
strings

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HTML Paragraph Formatting
• Formatting HTML source code, or final display in
the browser?
• Use escape characters (/n, /t, etc) to format source
HTML code
• Use HTML tags to format the final output in broswer
– <p>, <br>, …
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Dynamically Generating HTML
• Use Java programming capability to dynamically
generate HTML
– Dynamic content: date/time, user name, etc.
– Dynamic HTML elements (tags)
– Dynamic element attributes
– … (Be creative!)
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Getting User Data
• Two ways
– URL parameter (Get)
• http:// …/somefile?p1=value1&p2=value2
– HTML Form (Get or Post)
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Servlet
HTML Form
URL parameter
doGet
doPost
Post
User Input

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URL with Parameters
• User data can be sent with “get” request
– http:// …/somefile?p1=value1&p2=value2
• Applications
– Template page for data item details
• http://www.newegg.com/Product/Product.asp?Item=N82E16827152058
• http://www2.cis.gsu.edu/cis/people/display.asp?pk=3
– Page content selection
• http://forum.java.sun.com/category.jspa?categoryID=20
• http://javaweb.jackzheng.net/cis3270su06/index.jsp?page=schedule
– User input
• http://www.google.com/search?q=java
– Conditions/configuration
• http://finance.yahoo.com/q/bc?s=MSFT&t=5d&l=on&z=l&q=l
• http://msdn.e-academy.com/elms/Storefront/Home.aspx?campus=gsu_cis
– Page display/format, page content, error message, …
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Handling “Get” Parameter
• In HTTP “get”, user data are sent with URL
– http://…/GetData?p1=value1&p2=value2
• Using the request object (given by the doGet
method) to retrieve these data
– String p1=request.getParameter(“p1”);
– String p2=request.getParameter(“p2”);
– String p[ ]=request.getParameterValues(“p1”);
• Note: parameter names are case sensitive
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Number Conversion
• All parameter values are String type
– String p1=request.getParameter(“p1”);
• What if numbers are needed?
– Integer.parseInt()
– Double.parseDouble()
• Conversion exception needs to be handled

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Irregular Parameters
• Missing value (empty string is returned)
– …/GetData?data=
• Missing parameter (parameter undefined, null)
– …/GetData? // no parameter at all
– …/GetData?data // ”data” is still not defined
– …/GetData?Data=red // case sensitive
• Blanks
– …/GetData?data=hello world
• Redundant parameter
– …/GetData?data=blue&data=red // use
getParameterValues()
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JAVA SERVER PAGES
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What is JSP
• Servlets – HTML in java code
• JSP – java code in HTML
<HTML>
<HEAD>
<TITLE>Java Server Pages</TITLE>
</HEAD>
<BODY>
<H1>JSP</H1>
<%= “Java Server Pages.” %>
<HR>
</BODY>
</HTML>

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JSP Lifecycle
JSP to Servlet
Translation
Servlet
Compiled
Servlet
Loaded
jspInit()
called
_jspService()
called

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The need for JSP
• With servlets
– It is hard to write and maintain HTML
– Cannot use standard HTML tools
– HTML is inaccessible to non-java developers
Augu

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The benefits of JSP
• Easier to write and maintain HTML
• Can use standard HTML tools
• Can divide up development team

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Advantages
• The Java advantage
• Extensive API
• Easy to learn
• Big development community
• Standardization & server support

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Location of JSP pages
• Unlike servlets, JSP pages can be located in any of
the locations where HTML files can be put.

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JSP Scripting Elements
• JSP scripting elements enable us to insert java
code into JSP files.
• There are three types of elements
– Expressions <%= Java Expression %>
– Scriptlets <% Java Code %>
– Declarations <%! Field/Method %>

Web Engineering (703512)
JSP Expressions
• A JSP expression is used to insert java code directly into the
output.
Syntax
<%= Expression %>
Eg:
Current Time: <%= new java.util.Date() %>
Output:
Current Time: Tue Aug 22 21:05:47 IST 2006
• The expression is evaluated, converted to string and inserted
into the page.

Web Engineering (703512) August 30, 2021
Predefined Variables
• To simplify expressions, JSP provides a number
of predefined variables (implicit objects).
– request – the HttpServletRequest
– response – the HttpServletResponse
– session – the HttpSession
– out – the Writer (buffered version of type
JspWriter)
– application – the ServletContext
– config – the ServletConfig
– pageContext – introduced to give single point of
access to page attributes
– page – synonym for “this”

Web Engineering (703512)
JSP Scriptlets
• To something more than just output the value of a
simple expression.
• Allows the programmer to insert arbitrary code into the
servlets _jspService method.
Syntax:
<% Java Code %>
Eg:
<%
String str = request.getParameter(“name”);
out.print(“Name : ”+str);
%>
Augu

Web Engineering (703512)
JSP Declarations
• JSP declarations lets the programmer define methods or fields
that get inserted into the main body of the generated servlet
(outside the _jspService() method)
Syntax:
<%! Field/Method definition %>
Eg:
<%!
private String getMessage(){
return “This is a simple message!!”;
}
%>
<%= getMessage() %>

Web Engineering (703512)
XML Syntax
• XML like syntax for JSP expression, scriptlet &
declaration
– <jsp:expression>…</jsp:expression>
– <jsp:scriptlet>…</jsp:scriptlet>
– <jsp:declaration>…</jsp:declaration>
• Supported by JSP versio 1.2 & above
• These are case sensitive, should be in lowercase

Web Engineering (703512)
JSP Directives
• A JSP directive affects the overall structure of the
servlet that results from the JSP page.
• A JSP directive has the form:
– <%@ directive attribute=“value” … … %>
• There are three types:
– page, include & taglib

Web Engineering (703512)
JSP Page Directive
• The page directive controls the structure of the
servlet by importing classes, customizing the
superclass, changing content type, etc.
• The JSP Page directive has the following attributes:
– import, contentType, pageEncoding, session, isELIgnored,
buffer, autoFlush, info, errorPage, isThreadSafe, language
& extends

Web Engineering (703512)
JSP Page Directive Attributes
• import=“java.util.*, java.sql.*”
• contentType=“text/html; charset=ISO-8859-1”
• pageEncoding=“Shift_JIS”
• session=“true/false”
• isELIgnored=“false/true”
• buffer=“size in kb”
• autoFlush=“true/false”
• info=“Some info message.”
• errorPage=“error.jsp”
• isErrorPage=“false/true”
• isThreadSafe=“true/false”
• language=“java”
• extends=“package.class”

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Including Files
• There are three ways of including external files into
a JSP document.
– <jsp:include …>…
– <%@ include …>
– <jsp:plugin …>…

Web Engineering (703512)
The jsp:include Action
• This includes the output of a secondary page at the
time the main page is requested.
• The output of the sub page must be HTML
generated by a servlet or JSP.
<jsp:include page=“/inc/header.jsp”
flush=“true” />
<jsp:include page=“/inc/header.jsp”
flush=“true”>
<jsp:param name=“paramName” value=“xyz”>
</jsp:include>

Web Engineering (703512)
The Include Directive
• This includes directive is used to include a file in the
main JSP at the time of translation into a servlet.
• The code of the included file is added to that of the
JSP document.
<%@ include page=“/inc/header.jsp” %>

Web Engineering (703512)
Forwarding Requests
• This action is used to get the output of a JSP file
completely from another JSP or servlet.
• The output of the auxiliary JSP or servlet is sent to
the client, not that of the current JSP.
<jsp:forward page=“xyz.jsp” />

Web Engineering (703512)
The jsp:plugin Action
• Used to embed a java applet into the generated
output.
• Java applets are rarely used in web pages now a
days.
<jsp:plugin type=“applet”
code=“MyApplet.class”
width=“400” height=“300”>
</jsp:plugin>

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JAVA BEANS
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Java Beans
• What Are Beans?
• Beans are standard java objects.
– Must have a zero-arguments constructor.
– Should have no public fields.
– Values should be accessed through method calls, getXxx,
setXxx & isXxx.

Web Engineering (703512)
Java Bean (example)
public class Person {
private int age;
private String name;
… … …
public void setAge(int age){
this.age = age;
}
public void setName(String name){
this.name = name;
}
public int getAge(){
return this.age;
}
public String getName(){
return this.name;
}
… … …
}

Web Engineering (703512)
Using Java Beans & JSP
• There are three main constructs to use Java Beans
in JSP.
– <jsp:useBean ……… />
– <jsp:getProperty ……… />
– <jsp:setProperty ……… />

Web Engineering (703512)
jsp:useBean
• Used to load a bean to be used in the JSP document.
Syntax:
<jsp:useBean id=“name”
class=“package.Class” />
Eg:
<jsp:useBean id=“person”
class=“iiitmk.Person” />
Equivalent to:
<% iiitmk.Person person = new
iiitmk.Person(); %>

Web Engineering (703512)
Getting bean properties
• Used to read properties from beans.
Syntax:
<jsp:getProperty id=“name”
property=“propName” />
Eg:
<jsp:getProperty id=“person”
property=“name” />
Equivalent to:
<%= person.getName() %>

Web Engineering (703512)
Setting bean properties
• Used to set properties of beans.
Syntax:
<jsp:setProperty id=“name” property=“propName”
value=“propValue” />
Eg:
<jsp:setProperty id=“person” property=“name”
value=“Popeye The Sailor” />
Equivalent to:
<% person.setName(“Popeye The Sailor”); %>

Web Engineering (703512)
Properties & Request Parameters
• The value of a bean property can be set directly from
the value of the corresponding request parameter.
Syntax:
<jsp:setProperty id=“name”
property=“propName” param=“propName” />
Eg:
<jsp:setProperty id=“person”
property=“name” param=“name” />
<jsp:setProperty id=“person” property=“*”
/>

Web Engineering (703512)
Sharing Beans (scope)
• The scope of a bean defines where the bean is
stored and how it is accessible. By default it is
accessible as a local variable. Other places of
storing beans are the request, session and
application.
Syntax:
<jsp:useBean … … … scope=“…” />
Scopes:
page, request, session & application

Web Engineering (703512)
Page Scope
• The default scope of a bean. Bean is bound to a
local variable in the _jspService method and also
placed in the pageContext predefined variable,
accessible by calling getAttribute() method.
Syntax:
<jsp:useBean … … … scope=“page” />
<jsp:useBean … … … />

Web Engineering (703512)
Request Scope
• In addition to being bound to a local variable, the
bean is also placed in the HttpServletRequest object
(request) for the duration of the current request.
• Accessible by getAttribute() method.
Syntax:
<jsp:useBean … … … scope=“request” />

Web Engineering (703512)
Session Scope
• In addition to being bound to a local variable, the
bean is also placed in the HttpSession object
(session).
• Accessible by getAttribute() method.
Syntax:
<jsp:useBean … … … scope=“session” />

Web Engineering (703512)
Application Scope
• In addition to being bound to a local variable, the
bean is also placed in the ServletContext object
(application). The servlet context is shared by all
the JSP and servlets in the web application.
• Accessible by getAttribute() method.
Syntax:
<jsp:useBean … … … scope=“application”
/>

Web Engineering (703512)
WRAP-UP
That’s almost all for day…
60

Web Engineering (703512)
Bibliography
• Mandatory reading
– Java Servlet Tutorial
• http://java.sun.com/j2ee/tutorial/1_3-fcs/doc/Servlets.html
– Java Server Pages Tutorial
• http://java.sun.com/j2ee/tutorial/1_3-fcs/doc/JSPIntro.html
– Java Beans Tutorial
• http://java.sun.com/j2ee/tutorial/1_3-fcs/doc/JSPBeans.html
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Web Engineering (703512)
Tools
• Apache Tomcat
– http://tomcat.apache.org/
• Eclipse
– http://www.eclipse.org/
• Eclipse Web Tools
– http://www.eclipse.org/webtools/
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Web Engineering (703512)
Next Lecture
63
# Date Title Lecturer
1 7th Oct Web Engineering Introduction and Overview F. M. Facca
2 14h Oct Collection Requirements for Web Applications F. M. Facca
3 21st Oct Web Application Modeling F. M. Facca
4 28th Oct Developing Applications with WebML F. M. Facca
5 4th Nov Web Application Architectures I F. M. Facca
6 11th Nov Web Application Architectures II F. M. Facca
7 18th Nov Testing and Usability on the Web F. M. Facca
8 25th Nov Mid Term Exam F. M. Facca
9 2nd Dec Web Technologies I F. M. Facca
10 9th Dec Web Technologies II F. M. Facca
11 16th Dec Web Technologies III F. M. Facca
12 13th Jan Web 2.0 Mash-ups F. Daniel (UNITN)
13 20th Jan Web Application Development Process/
Project Management for Web Applications
F. M. Facca
14 27th Jan Final Exam F. M. Facca

Web Engineering (703512)
Questions?
64