CSM-15_Lecture_8_old

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Transcript CSM-15_Lecture_8_old 

Component-Based
Software Engineering
Internet Applications
Paul Krause
Lecture 8 Internet Applications
Contents
 Reminder of Client-Server architectures
 Client-side programming with Applets and
JavaScript
 Server-side programming with JSP and
Servlets
Client/server Architecture
Client
Client
Internet
Internet
Browser,
Applets, …
Browser,
Applets, …
Server
Database, servlets, …
Generic 5-tier Architecture
Client Tier
Presentation
Business Rules
Integration
Resources
Application Components

Web pages



Program components




HTML + scripting language code
Provides dynamic processing of data and modification
of visual appearance
Perform the main computations
Receive input from HTML forms
Present output as web-pages
Configuration files

Enables application to be quickly deployed on
different servers
Types of Program Component

Controller components


e.g. selection and customisation of the web-pages to
return to the client
Session beans

encapsulate information and operations specific to a
client session
• stateless session beans - e.g. check data entry
• stateful session beans - e.g. shopping cart

Entity beans

provide access to persistent data
A statefull session bean
public class BasketBean {
private HashMap contents = new HashMap;
public void addItem(Long itemid) { … }
public void updateItem(Long itemid, int quantity)
{…}
public Set getItems( ) { … }
public int getQuantity(Long itemid) { … }
public void deleteItem(Long itemid) { … }
public int numberOfItems( ) { … }
}
Internet Programming in Java
 Java-based
technologies include:
 Client-side:


Applets
JavaScript
 Server-side:


JSP - Java Server Pages
Java Servlets
Lecture 8 Internet Applications
Contents
 Reminder of Client-Server architectures
 Client-side programming with Applets and
JavaScript
 Server-side programming with JSP and
Servlets
HelloFromVenus.java
import java.awt.*;
import java.applet.Applet;
// Copyright (c) 1999-2002, Xiaoping Jia.
public class HelloFromVenus extends Applet {
public void paint(Graphics g) {
Dimension d = getSize();
g.setColor(Color.black);
g.fillRect(0,0,d.width,d.height);
g.setFont(new Font("Helvetica", Font.BOLD, 24));
g.setColor(new Color(255, 215, 0)); // gold color
g.drawString("Hello From Venus!", 40, 25);
g.drawImage(getImage(getCodeBase(), "Venus.gif"),
20, 60, this);
}
}
Invoking the Applet
<HTML>
<HEAD>
<TITLE>
Object-Oriented Software Development Using Java | HelloFromVenus
Applet
</TITLE>
</HEAD>
<BODY BGCOLOR=BLACK TEXT=white>
<CENTER>
<H2>Here is the <EM>Hello From Venus</EM> Applet</H2>
<APPLET CODE="HelloFromVenus.class" WIDTH=300 HEIGHT=350>
</APPLET>
</CENTER>
&nbsp; &nbsp; &nbsp; &nbsp; Venus photo courtesy of NASA.
</BODY>
</HTML>
JavaScript
 Notation
is close to Java, although with
some important differences


no explicit types for variables
simplified structure to the code - a “scripting
language”
But provides a powerful client-side
processing and scripting language
 Following examples from Lano et al,
Software Design Using Java 2

<! DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0
Transitional//EN">
<HTML>
<HEAD>
<TITLE>Date Check Program</TITLE>
<SCRIPT LANGUAGE = "JavaScript">
// Some Java-like processing stuff goes in here
// …
</SCRIPT>
</HEAD>
<BODY>
Click Refresh or Reload to run script again
</BODY>
</HTML>
var firstNumber, secondNumber, number1, number2;
firstNumber = window.prompt("Enter month (1--12)", "1");
secondNumber = window.prompt("Enter day (1--31)", "1");
number1 = parseInt(firstNumber);
number2 = parseInt(secondNumber);
if (1 <= number2 && number2 <= 31 &&
(number1 == 1 || number1 == 3 || number1 == 5 ||
number1 == 7 || number1 == 8 || number1 == 10 ||
number1 == 12))
{ document.writeln("<H1>Date is correct</H1>"); }
else if (1 <= number2 && number2 <= 30 &&
(number1 == 4 || number1 == 6 || number1 == 9 || number1 == 11 ))
{ document.writeln("<H1>Date is correct</H1>"); }
else if (1 <= number2 && number2 <= 29 && number1 == 2 )
{ document.writeln("<H1>Date is correct</H1>"); }
else
{ document.writeln("<H1>Date is not correct!</H1>"); }
Browser Events
Event
HTML Syntax
Page is loaded
<BODYONLOAD = “function( )”>
Button is pressed
<INPUTTYPE = “button”
VALUE = “command”
ONCLICK = “function( )”>
<BODYONMOUSEMOVE =
“function( )”>
Mouse is moved
Mouse over element <…ONMOUSEOVER = “function( )”>
Form entry active
<INPUT…ONFOCUS = “function()”>
Lecture 8 Internet Applications
Contents
 Reminder of Client-Server architectures
 Client-side programming with Applets and
JavaScript
 Server-side programming with JSP and
Servlets
JavaServer Pages (JSP)
 Works
on the Server side to add
functionality to HTML pages
 Typically, JSP is used to add more
complex functionality than JavaScript
 JSP has a much closer relationship with
Java Beans:


Beans can be invoked from within JSP files
Indeed, this is recommended to separate the
GUI (html) from back-end code (Beans)
What does being a Bean mean?
 In
this context it is simply an instance of a
Java class, conforming to an agreed
pattern:



The class has a no argument constructor
Properties are accessed through “get”
methods (“is” methods in the case of
booleans)
Properties are updated through “set” methods
 A JSP
file then knows how to interface to it
A Booking Bean
public class BookingBean {
private int month;
private int day;
private String name;
private String number;
private boolean smoking:
public BookingBean( ) { }
// no argument constructor
public void setMonth(String mon)
{month = Integer.parseInt(mon); }
public String getMonth( )
{return “ “ + month;} …
Using a Bean in JSP
 Within
a Java Server Page, we may wish
to update and read a particular instance of
the BookingBean class.
 There is a simple mapping from lines in a
JSP script, and the equivalent Java
statements
 This mapping is enabled by usage of the
Java Bean coding guidelines
Creating and updating a Bean
<jsp : useBean id = “booker” class = “BookingBean”/>
Corresponds to the Java statement:
BookingBean booker = new BookingBean( );
<jsp : setProperty name = “booker” property = “month”
param = “month”/>
Corresponds to the Java statement:
booker.setMonth(request.getParameter(“month”));
Note, in this last case request is a Java object
representing an HTTP request
Example jsp file
<jsp : useBean id = “booker” class = “BookingBean”/>
<jsp : setProperty
name = “booker” property = “month” param = “month”/>
<jsp : setProperty
name = “booker” property = “day” param = “day”/>
// …
<HTML>
<HEAD><TITLE>Echo Parameters</TITLE></HEAD>
<BODY>
Thank you, <jsp:getProperty name = “booker” property =
“name” /> for your booking. You requested …
Java Servlets
 Servlets
use Java packages for server
side processing of internet applications
 This is a pure Java approach, rather than
the hybrid Java/HTML approach of JSP
 Can therefore write better structured, and
easier to debug applications
Summary

A quick survey of Java technologies for Internet
Applications
 We saw the different needs of:



client-side programming - relatively light-weight
processes for data validation and gui configuration
server-side programming - more computationally
intensive applications with access to persistent data
sources
Structure these applications using ideas from
Software Components to avoid a serious mess!