Web Engineering

Web EngineeringWeb 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

Overview

• Servlet• JSP• Java Beans• Wrap-up

SERVLETS

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”

Web Engineering (703512)6

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

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{ … }

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

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

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

“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”

<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>

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)

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

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, …

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 … )

Response Processing

• Response body– Generating HTML or other content for display

• Response header– Manipulating response message header data to affect its

behavior

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>”);

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

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>, …

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!)

Getting User Data

• Two ways– URL parameter (Get)

• http:// …/somefile?p1=value1&p2=value2

– HTML Form (Get or Post)

Servlet

HTML Form

URL parameter

doPostPost

GetUser Input

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, …

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

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

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()

JAVA SERVER PAGES

What is JSP

• Servlets – HTML in java code• JSP – java code in HTML

<TITLE>Java Server Pages</TITLE></HEAD><BODY>

</BODY></HTML>

JSP Lifecycle

JSP to ServletTranslation

ServletCompiled

ServletLoaded

jspInit()called

_jspService()called

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

April 20, 2023

The benefits of JSP

• Easier to write and maintain HTML• Can use standard HTML tools• Can divide up development team

Advantages

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

Location of JSP pages

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

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 %>

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) April 20, 2023

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”

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 %>

String str = request.getParameter(“name”);out.print(“Name : ”+str);

April 20, 2023

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() %>

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

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

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

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”

Including Files

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

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>

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” %>

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” />

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>

JAVA BEANS

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.

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;}

… … …}

Using Java Beans & JSP

• There are three main constructs to use Java Beans in JSP.– <jsp:useBean ……… />– <jsp:getProperty ……… />– <jsp:setProperty ……… />

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(); %>

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() %>

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”); %>

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=“*” />

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

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 … … … />

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” />

Session Scope

• In addition to being bound to a local variable, the bean is also placed in the HttpSession object (session).

Syntax:<jsp:useBean … … … scope=“session” />

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.

Syntax:<jsp:useBean … … … scope=“application” />

WRAP-UPThat’s almost all for day…

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

• Apache Tomcat– http://tomcat.apache.org/

• Eclipse– http://www.eclipse.org/

• Eclipse Web Tools– http://www.eclipse.org/webtools/

Next Lecture

# 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

Questions?

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