Transcript Using Ada and JGNAT to develop web applications using JDBC, JSP

Developing Web Applications
Using Ada, JGNAT, JavaServer Pages,
and JDBC to Build Web Applications
Terry Westley
SIGAda 2001
What Will You Learn?
• Overview of dynamic web technologies
• Create HTML pages that use JavaServer
Pages (JSP) technology to access and
display dynamic web content
• Write Java Beans and Java servlets in Ada
• Use JDBC in Ada to create, maintain, and
query a relational database
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Tutorial Prerequisites
• We assume you are familiar with:
– Creating static HTML pages
– Programming in Ada
• But, not:
– Programming in Java
– SQL
– JavaServer Pages
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References
• DuBois, Paul, MySQL, New Riders, Indianapolis, IN, 2000.
• Fields, Duane K., Kolb, Mark A., Web Development with
JavaServer Pages, Manning Publications Co., Greenwich, CT,
2000.
• Goodman, Danny, Dynamic HTML, The Definitive Reference,
O'Reilly and Associates, Sebastopol, CA, 1998.
• Horstmann, Cay S., Cornell, Gary, Core Java 1.1, Volume I -Fundamentals, Prentice Hall, Upper Saddle River, NJ, 1997.
• Lemay, Laura, Perkins, Charles L., Morrison, Michael, Teach
Yourself Java in 21 Days, Professional Reference Edition, Sams
Publishing, Indianapolis, IN, 1996.
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Table of Contents
Dynamic Web Technologies
• Required Components
• Introduction to JSP
• Introduction to Java Beans
• Introduction to JDBC
• Building a Web Application
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What is a Dynamic Web?
What do I mean by "dynamic?"
• User interaction affects the HTML page
• Data from a server affects the HTML page
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Dynamic Web Technologies
•
•
•
•
•
•
•
Static HTML pages
Common Gateway Interface (CGI)
JavaScript
Java applets
Dynamic HTML (DHTML)
Java servlets
Template systems
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Static HTML
• Browser requests an HTML document
• Server finds the file and sends it to browser
via HTTP
• Server sends image files separately
• Static HTML example
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Static HTML
Browser
Server
Page Request
Page
Image
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Common Gateway Interface (CGI)
• Server-side processing
• Usually used in conjunction with HTML forms
• HTTP request is passed to a separate program
which processes it and generates a response
• David Wheeler's AdaCGI:
– http://www.dwheeler.com/
• CGI example
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Common Gateway Interface (CGI)
Browser
Server
Page Request
Spawn
CGI Program
HTTP Request
Page
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Page
11
JavaScript
• Client-side processing (in browser)
• First introduced by Netscape
• Object-based language with access to
Document Object Model (DOM)
• Small application whose source code is
embedded in an HTML page and interpreted
by the browser
• JavaScript example
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JavaScript
Browser
Server
Page Request
Page
Image
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Java Applets
• Client-side processing
• Small applications that server sends to browser as
a separate file
• Browser invokes the Java Virtual Machine to
execute the applet
• Applet may or may not have a user interface
• Applet is discarded when user switches to another
page
• Java Applet example
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Java Applets
Java Virtual
Machine
Browser
Server
Page Request
Page
Applet
Applet
User Interface
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Dynamic HTML (DHTML)
• Client-side processing
• DHTML is a combination of World Wide
Web Consortium (W3C) standards for:
–
–
–
–
HTML 4.0
JavaScript
Document Object Model (DOM)
Cascading Style Sheets (CSS)
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Dynamic HTML (DHTML)
Browser
Server
Page Request
Page
Image
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Java Servlets
• Server-side processing
• Small Java applications that server executes
• Similar to CGI except does not require
spawning a new process
• Servlet processes the HTTP request and
generates the response
• Java servlet example
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Java Servlets
Browser
Java Servlet
Container
Server
Page Request
HTTP Request
Page
Spawn
Servlet
Thread
Page
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Template Systems
• Server-side processing
• Embedded in HTML file:
– Special tags request dynamic content
– Scripts generate more HTML
• Server processes the HTML file, filling in
the dynamic content and executing the
scripts, then passing the page to the browser
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Template Systems
Browser
Template
Processor
Server
Page Request
HTTP Request
Page
Page
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Template Systems
•
•
•
•
•
•
•
ColdFusion
Microsoft Active Server Pages (ASP)
Server Side JavaScript
PHP
WebMacro
Apache Velocity
JavaServer Pages
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Why JavaServer Pages?
• Platform-independent technology
• Java-based technology
– Full object-oriented programming model
– Access to Java platform, including all Java
APIs
• Improved performance over CGI and
scripting languages
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Why JavaServer Pages (2)
• A programming model which provides for
– Separation of presentation and implementation
– Reusable component model: Java Beans
– Tag extension mechanism
• Last, but not least:
– Use Ada to code Java Beans and Java servlets
– Complete set of free tools
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Table of Contents
• Dynamic Web Technologies
Required Components
• Introduction to JSP
• Introduction to Java Beans
• Introduction to JDBC
• Building a Web Application
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Required Components
• Java Software Development Kit (SDK)
• Ada to JVM compiler
– JGNAT
– Aonix ObjectAda
• Relational database – MySQL
• JDBC driver
• JSP-enabled web server – Jakarta Tomcat
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Java SDK
• Get “Java 2 Standard Edition”
– Windows version: j2sdk1_3_0-win.exe
– http://java.sun.com
• Install on
– server
– development computer
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Test Java SDK Installation
• Create file HelloJavaWorld.java:
class HelloJavaWorld {
public static void main (String args[]) {
System.out.println ("Hello Java World!");
}
}
• Compile it:
javac HelloJavaWorld
• Execute it:
java HelloJavaWorld
• Should display:
Hello Java World!
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Ada to JVM Compiler
• Ada compiler targeted to the Java Virtual
Machine (JVM)
– JGNAT by Ada Core Technologies
– Aonix ObjectAda
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JGNAT
• Get JGNAT
– Windows version: jgnat-1.1p-nt.exe
– ftp://ftp.cs.nyu.edu/pub/gnat/jgnat/
– ftp://ftp.freesoftware.com/pub/ada/compiler/gna
t/distrib/jgnat/
• Install on development computer only
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JGNAT Environment Variables
• Remove:
– ADA_INCLUDE_PATH
– ADA_OBJECTS_PATH
Dot is important;
don’t leave it out!
• Add to PATH:
– SET PATH=C:\JGNAT-1.1P\BIN;%PATH%
• Add CLASSPATH:
– SET CLASSPATH=.;C:\JGNAT1.1P\LIB\JGNAT.JAR;%CLASSPATH%
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Test JGNAT Installation
• Create file hello.adb:
with Ada.Text_IO;
procedure HelloJGNAT is
begin – HelloJGNAT
Ada.Text_IO.Put_Line (“Hello, JGNAT World!");
end HelloJGNAT;
• Compile it:
jgnatmake hellojgnat
• Execute it:
java hellojgnat
• Should display:
Hello, JGNAT World!
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Get MySQL
• MySQL is an open-source (GPL) relational database
(http://www.mysql.com)
• Also available with non-GPL commercial license
• Support available from TcX DataKonsult AB
• See excellent user reference manual in Docs
directory for installation, testing instructions and a
tutorial
• Install on server and development computers
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MySQL Security
• Remove anonymous user
– mysql> delete from mysql.user where user=“”;
• Give root a password
– shell> mysqladmin –u root password <password>
• Require passwords of all users and grant only
needed privileges
– Generally, only select, update, delete, and insert
– mysql> grant select, update, delete, insert on
<database> to <user> identified by “<password>”;
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JDBC Driver
• Java driver that supports Java API for using
ODBC to connect to relational databases
• Check http://www.mysql.com/ for available JDBC
drivers for MySQL
• For this tutorial, we will use Mark Matthews'
driver found at
http://www.worldserver.com/mm.mysql/
• Install on server and development computers
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Get Jakarta Tomcat
• An open-source (Apache Software
Foundation) implementation of Sun's
reference edition JSP-enabled web server
– http://jakarta.apache.org/
• Can be run stand-alone or from within
Apache
• Install on server and development computers
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Tomcat Environment Variables
• Set environment variables
– SET TOMCAT_HOME=C:\PROGRA~1\JAKARTA-TOMCAT
– SET JAVA_HOME=C:\JDK1.3
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Windows 95/98/ME
• Use bin\startup.bat to start Tomcat
• Use bin\shutdown.bat to stop Tomcat
• May have to increase "Initial environment"
memory size of startup.bat and
shutdown.bat scripts to 2816
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Windows 2000/XP
• Can run Tomcat as a service
• See instructions in Tomcat documentation
for installation and configuration
– wrapper.tomcat_home
– wrapper.java_home
– wrapper.class_path
• Example: wrapper.properties
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Test Tomcat
• Start web server using startup.bat script from
Tomcat bin directory
• Start web browser
• Go to http://localhost:8080/ to see local Tomcat
home page
• Try out some of the JSP and servlet examples
• To shutdown web server, use shutdown.bat script
from Tomcat bin directory
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Table of Contents
• Dynamic Web Technologies
• Required Components
Introduction to JSP
• Introduction to Java Beans
• Introduction to JDBC
• Building a Web Application
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My First JSP
<HTML>
<BODY>
Hello, World!
</BODY>
</HTML>
• JSP example
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Interactive JSP
<HTML>
<BODY>
<% String visitor =
Script
request.getParameter("name");
if (visitor == null)
visitor = "World";
%>
Hello, <%= visitor %>
</BODY>
</HTML>
Tag
See Interactive JSP example
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JSP Processing
Browser
JSP
Container
Server
Page Request
HTTP Request
Page
Page
Developing Web Applications with Ada
Compile
Page
Spawn
Servlet
Thread
44
Factorial
• Another JSP example
• Compute and display factorials
• All Java code in JSP document
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The Bean Edition
<html>
<body>
<jsp:useBean id="hello"
class="hellobean$typ"/>
<jsp:setProperty name="hello"
property="name"
param="name"/>
Hello,
<jsp:getProperty name="hello"
property="name"/>!
</body>
</html>
See Bean example
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JSP Bean Processing
Browser
JSP
Container
Server
Page Request
HTTP Request
Compile Page
Spawn Servlet Thread
Create
Page
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Page
Bean
setProperty
getProperty
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JSP Script Tags
• Declarations
<%! String visitor %>
• Scriptlets
<% visitor = request.getParameter("name");
if (visitor == null)
visitor = "World"; %>
• Expressions
<%= visitor %>
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JSP XML Tags
• Declarations
<jsp:declaration> String visitor </jsp:declaration>
• Scriptlets
<jsp:scriptlet>
visitor = request.getParameter("name");
if (visitor == null)
visitor = "World";
</jsp:scriplet>
• Expressions
<jsp:expression> visitor </jsp:expression>
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JSP Bean Tags
• Create a bean
<jsp:useBean id="hello"
class="hellobean$typ"/>
• Set bean property
<jsp:setProperty name="hello"
property="name"
param="name"/>
• Get bean property
<jsp:getProperty name="hello"
property="name"/>
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Dynamic Web Technologies
Technology
User
Access Language Separation
Interaction To Server
Static HTML
CGI
No
Yes
No
Yes
None
Any
N/A
Yes
JavaScript
Java Applet
Java Servlet
JSP Script
Java Beans
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
JavaScript
Java, Ada
Java, Ada
Java
Java, Ada
No
Yes
No
No
Yes
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Other
Fast load
CPUexpensive
Fast load
Slow load
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Table of Contents
• Dynamic Web Technologies
• Required Components
• Introduction to JSP
Introduction to Java Beans
• Introduction to JDBC
• Building a Web Application
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Introduction to Java Beans
• Software components written in Java Ada
• A Java Bean is a Java class that adheres to
the JavaBeans API specification
– http://java.sun.com/products/javabeans/
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Bean Containers
• Tools that provide Bean composition and
Bean execution
• Each implementation has its own limitations
on how it interacts with Beans, but…
• Interaction is primarily through Bean
properties and their set and get operations
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Bean Properties
• Properties can be pretty much any data type
• They can be indexed to provide access
collections of values
• Some properties trigger behavior
• The JSP container is one such Bean container
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JSP Bean Processing
Browser
JSP
Container
Server
Page Request
HTTP Request
Compile Page
Spawn Servlet Thread
Create
Page
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Page
Bean
setProperty
getProperty
56
JSP Scriptlets and Beans
• Can call any function in the bean interface
• Can call set and get properties returning any
data type
• Expressions returning primitive types are
converted to String type by the JSP
container
• But, you're really writing Java code
• See Roll Dice example
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JSP XML Tags
• JSP XML tags treat all properties as String
data type exclusively
• Works well with HTML!
• For all properties, the Bean must provide
String type set and get operations
• See Roll Dice example
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Bean Types
• Visual components
– Implement graphical user interface elements
– Not compatible with JSP
• Data storage
– An object that provides access to information
• Service beans
– Implement the behavior of a JSP application
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Using Java Beans
•
•
•
•
•
Using a Java Bean
Initializing a Java Bean
Java Bean properties
Mixing Bean tags and scriptlets
Java Bean scope
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Using a Java Bean
The <jsp:useBean> tag
<jsp:useBean id="dice" class="randombean$typ"/>
Local bean name
Class name of the bean
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UseBean Tag Attributes
Attribute Value
id
Java identifier
Default Example
None
dice
class
Java class name
None
scope
page, request,
page
session, application
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randombean$typ
session
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UseBean Tag Example
<html>
<head>
<title> Roll Dice </title>
<link rel="stylesheet" type="text/css" href="dice.css">
</head>
<body>
<jsp:useBean id="dice" class="randombean$typ"/>
<jsp:setProperty name="dice" property="minint" value="1"/>
<jsp:setProperty name="dice" property="maxint" value="6"/>
<table>
<tr>
<td> <%= dice.getint() %>
<td> <jsp:getProperty name="dice" property="int"/>
</table>
</body>
</html>
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The useBean Tag
• Creates an instance of a bean
– Executes the object constructor
• Assigns an ID local to the page
• Can have more than one instance of a bean
on a page
• Its lifetime has scope
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Initializing a Java Bean
The <jsp:setProperty> tag
Local bean name
<jsp:setProperty name="dice"
property="minint"
value="1"/>
Property value
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Property name
65
Initializing Bean Example
<html>
<head>
<title> Roll Dice </title>
<link rel="stylesheet" type="text/css" href="dice.css">
</head>
<body>
<jsp:useBean id="dice" class="randombean$typ"/>
<jsp:setProperty name="dice" property="minint" value="1"/>
<jsp:setProperty name="dice" property="maxint" value="6"/>
<table>
<tr>
<td> <%= dice.getint() %>
<td> <jsp:getProperty name="dice" property="int"/>
</table>
</body>
</html>
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Initializing Bean Alternative
<html>
<head>
<title> Roll Dice </title>
<link rel="stylesheet" type="text/css" href="dice.css">
</head>
<body>
<jsp:useBean id="dice" class="randombean$typ">
<jsp:setProperty name="dice" property="minint" value="1"/>
<jsp:setProperty name="dice" property="maxint" value="6"/>
</jsp:useBean>
<table>
<tr>
<td> <%= dice.getint() %>
<td> <jsp:getProperty name="dice" property="int"/>
</table>
</body>
</html>
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Initializing a Java Bean
• Constructor methods called by JSP do not
have any parameters
• Initialization of bean must be done through
properties
• Use a Set property function to initialize any
property
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Using Request Parameters
Request is:
<a href="HelloBean.jsp?name=Westley">Java Bean</a>
Can initialize bean property from request parameter:
<jsp:setProperty name="hello"
property="name"
param="name"/>
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Java Bean Properties
The <jsp:getProperty> tag
Local bean name
<jsp:getProperty name="dice" property="int"/>
Property name
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Mixing Bean Tags and Scriptlets
<html>
<head>
<title> Roll Dice </title>
<link rel="stylesheet" type="text/css" href="dice.css">
</head>
<body>
<jsp:useBean id="dice" class="randombean$typ"/>
<jsp:setProperty name="dice" property="minint" value="1"/>
<jsp:setProperty name="dice" property="maxint" value="6"/>
<table>
<tr>
<td> <%= dice.getint() %>
<td> <jsp:getProperty name="dice" property="int"/>
</table>
</body>
</html>
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Java Bean scope
• Can specify that a Bean’s “life” extends
beyond the scope of the current page
• Use the scope attribute in the
<jsp:useBean> tag
• Choices: page, request, session, application
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Java Bean Scope
Scope
Accessibility
Life span
Page
Current page
Until page is displayed
Request
Current page and included or
forwarded pages
Session
Current request and
subsequent requests from
same browser window
Current and future requests
that are part of same web
application
Until request has been
processed and response
sent to user
User’s session
Application
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Application
73
Writing Java Beans
•
•
•
•
•
What is a Bean?
Bean constructor
Initializing Beans
Bean properties
Testing with JUnit
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What is a Bean?
• A Java class that follows a set of naming
and design conventions
• Not required to inherit from a specific class
or implement a specific interface
• Just follow the conventions
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Bean Conventions
• Java Bean is a Java class
• Implement a constructor that takes no arguments
– May implement other constructors as well
• Define Bean properties by defining access and
update methods
– Implement public method with property name prefixed
by set and get as needed
• May define other methods, such as indexed
properties, but they are not accessible via JSP tags
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A Java Bean is a Java Class
with Java.Lang.Object;
with Java.Util.Random;
package RandomBean is
type Typ is
Random :
MinInt :
MaxInt :
end record;
type Ref is
new Java.Lang.Object.Typ with record
Java.Util.Random.Ref;
Java.Int;
Java.Int;
access all Typ'Class;
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Bean Constructor Specification
An Ada function with these characteristics:
– Result type is an access type designating a class-wide type
– Only one parameter, named This, whose type is the same
as the result type and has a null default value
– Specifies pragma Java_Constructor
function new_RandomBean (
This : Ref := null) return Ref;
pragma Java_Constructor (new_RandomBean);
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Bean Constructor Body (1)
First statement of a Java constructor must be either a call
to another constructor of the class or a call to a
constructor of the superclass
function new_RandomBean (
This : Ref := null) return Ref is
Super : Java.Lang.Object.Ref :=
Java.Lang.Object.new_Object (
Java.Lang.Object.Ref (This));
begin -- new_RandomBean
This.Random := Java.Util.Random.New_Random;
This.MinInt := 1;
This.MaxInt := Java.Int'Last;
return This;
end new_RandomBean;
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Bean Constructor Body (2)
Then, initialize the object and return it
function new_RandomBean (
This : Ref := null) return Ref is
Super : Java.Lang.Object.Ref :=
Java.Lang.Object.new_Object (
Java.Lang.Object.Ref (This));
begin -- new_RandomBean
This.Random := Java.Util.Random.New_Random;
This.MinInt := 1;
This.MaxInt := Java.Int'Last;
return This;
end new_RandomBean;
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Bean Constructor is Invoked
<html>
<head>
<title> Roll Dice </title>
<link rel="stylesheet" type="text/css" href="dice.css">
</head>
<body>
<jsp:useBean id="dice" class="randombean$typ"/>
<jsp:setProperty name="dice" property="minint" value="1"/>
<jsp:setProperty name="dice" property="maxint" value="6"/>
<table>
<tr>
<td> <%= dice.getint() %>
<td> <jsp:getProperty name="dice" property="int"/>
</table>
</body>
</html>
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Initializing Beans
Since the constructor must have no arguments,
you will likely need to call property setter
functions to initialize the Bean.
procedure SetMinInt (This : access Typ;
Min : in Java.Int) is
begin – SetMinInt
This.MinInt := Min;
end SetMinInt;
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Initializing Bean
<html>
<head>
<title> Roll Dice </title>
<link rel="stylesheet" type="text/css" href="dice.css">
</head>
<body>
<jsp:useBean id="dice" class="randombean$typ"/>
<jsp:setProperty name="dice" property="minint" value="1"/>
<jsp:setProperty name="dice" property="maxint" value="6"/>
<table>
<tr>
<td> <%= dice.getint() %>
<td> <jsp:getProperty name="dice" property="int"/>
</table>
</body>
</html>
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Bean Properties
Now that our Bean is initialized, use a property
getter function to fetch a property value and
insert it into the JSP page.
function GetInt (This : access Typ)
return Java.Int is
begin – GetInt
return
Java.Util.Random.NextInt (This.Random,
This.MaxInt-This.MinInt+1) +
This.MinInt;
end GetInt;
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Bean Properties
<html>
<head>
<title> Roll Dice </title>
<link rel="stylesheet" type="text/css" href="dice.css">
</head>
<body>
<jsp:useBean id="dice" class="randombean$typ"/>
<jsp:setProperty name="dice" property="minint" value="1"/>
<jsp:setProperty name="dice" property="maxint" value="6"/>
<table>
<tr>
<td> <%= dice.getint() %>
<td> <jsp:getProperty name="dice" property="int"/>
</table>
</body>
</html>
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JSP Type Conversions
Type
Conversion to String
Conversion from String
Boolean
Byte
Char
Double
Int
Float
Long
Java.lang.Boolean.toString
Java.lang.byte.toString
Java.lang.character.toString
Java.lang.double.toString
Java.lang.integer.toString
Java.lang.float.toString
Java.lang.long.toString
Java.lang.Boolean.valueOf
Java.lang.byte.valueOf
Java.lang.character.valueOf
Java.lang.double.valueOf
Java.lang.integer.valueOf
Java.lang.float.valueOf
Java.lang.long.valueOf
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Testing with JUnit
• JUnit is a regression testing framework
– http://www.junit.org/
• For languages other than Java, see
– http://www.xprogramming.com/software.htm
• For Ada, see Ed Falis’ AUnit
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Generating Ada Specs
• JUnit is a jar file, junit.jar, from which we
need to generate Ada package specs
• JGNAT includes the tool, jvm2ada, for this
purpose
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Using jvm2ada
• Create a directory and copy junit.jar into the
directory
• Unzip junit.jar and rezip without file compression
• Generate Ada package specs
jvm2ada junit.jar
• Compile all the package specs
for f in *.ads ; do
jgnatmake -I/JSP/java-APIs/java $f
done
• See jar2ada.sh script
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Using JUnit with Ada
• Create an Ada package with a tagged type
derived from JUnit.Framework.TestCase
• Add appropriate constructor
• Add setUp method
• Add one test method for each test case
• RandomBeanTest example
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90
Table of Contents
• Dynamic Web Technologies
• Required Components
• Introduction to JSP
• Introduction to Java Beans
Introduction to JDBC
• Building a Web Application
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91
Introduction to JDBC
•
•
•
•
•
•
•
Establishing a connection
JDBC statements
Creating a table
Updating a table
Query
Result sets
Prepared statements
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Establishing a Connection
• Load the driver
Obj := Java.Lang.Class.NewInstance (
Java.Lang.Class.forName(
+"org.gjt.mm.mysql.Driver"));
• Make the connection
Con := Java.Sql.DriverManager.
getConnection(
URL, User, Password);
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JDBC Statements
• A Statement object sends SQL statements to
the database server
• Create a statement, then execute it
• You must choose the appropriate execute
method:
– executeQuery for SELECT statements
– executeUpdate for statements that update or
modify tables
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Create a Statement Object
declare
Con : Java.Sql.Connection.Ref;
Stmt : Java.Sql.Statement.Ref;
begin
Con := Java.Sql.DriverManager.
getConnection(
URL, User, Password);
Stmt := Java.Sql.Connection.
createStatement (Con);
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Execute a Statement
Stmt := Java.Sql.Connection.
createStatement (Con);
Result := Java.Sql.Statement.
executeUpdate(Stmt,
+("drop table messages"));
• Full Example: DropMessages
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Creating a Table
Result := Java.Sql.Statement.
executeUpdate(Stmt, +(
"create table messages (" &
"
MessageID int unsigned not
"
auto_increment primary
"
Posted
timestamp
"
Subject
varchar(255) not
"
Body
text
not
null " &
key, " &
," &
null," &
null)"));
• Full Example: CreateMessages
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Updating a Table
Result := Java.Sql.Statement.
executeUpdate (Stmt, +(
"INSERT INTO Messages " &
"(Subject, Body) VALUES " &
"('test subject', 'test body')"));
• Full Example: InsertMessages
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Query
Result := Java.Sql.Statement.
executeQuery (Stmt, +(
"SELECT * FROM Messages");
• Where are the rows that are returned?
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Result Sets
• JDBC returns results from SELECT in a
ResultSet
• Must declare an instance of ResultSet
• Execute a query
• Iterate over the Result Set, fetching the data
• Example: QueryMessages
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Result Sets
• Get methods for Java types: byte, short, int,
long, float, double, boolean, string, date,
time, et. al.
• Match get method with database type
• Can use column name instead of position:
Java.Sql.ResultSet.GetInt (
Results, +“MessageID”);
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Prepared Statements
• For when you need to repeat the same SQL
statement many times
• A Prepared Statement is given an SQL
statement when it is created:
Stmt := Java.Sql.Connection.
PrepareStatement (Con, +(
"INSERT INTO Messages " &
"(Subject, Body) VALUES " &
"(?, ?)"));
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Prepared Statement
• Supply field values:
Java.Sql.PreparedStatement.
SetString (Stmt, 1, +"subject 3");
Java.Sql.PrepareStatement.
SetString (Stmt, 2, +"body 3");
• Execute the Prepared Statement
Rows := Java.Sql.PreparedStatement.
ExecuteUpdate (Stmt);
• Example: PrepInsertMessages
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Table of Contents
• Dynamic Web Technologies
• Required Components
• Introduction to JSP
• Introduction to Java Beans
• Introduction to JDBC
Building a Web Application
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Building a Web Application
• Model-View-Controller architecture
• Page-centric design
• Servlet-centric design
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Model-View-Controller
• Model
– Models data and business process
• Controller
– Mediates between Model and View
– Controls application’s flow
• View
– Client side display (HTML or XHTML)
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Page-Centric Design
• Application is composed of a set of related
JSP pages
• All application logic is hard-coded in the
JSP pages through its scripts, beans, and
expressions
• Each page has a specific role to play
• Example: Discussion Group
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View
index.html
Discussion Group
Post New Message
post.html
Controller
post.jsp
Model
Message
Controller
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Message
Table
Database
108
View
Discussion Group
Read Messages
index.html
Controller
msgindex.jsp
Message
Bean
read.jsp
Model
Message
Controller
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Message
Table
Database
109
Servlet-Centric Design
• JSP pages used only for presentation (view)
• All application logic (model and controller)
is implemented in servlets
• Requests are routed through one or more
servlets which control application flow and
which pages are displayed when
• Still use beans for communication between
servlet and a JSP page
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Servlet Functions
• Perform actions on behalf of a JSP page
• Deliver data for display to a JSP page
• Control application flow between related
JSP pages
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Servlet Benefits
• Provides better separation of presentation
and application logic
• Reduces complexity of JSP page code
• Better control of error handling
• Example: HelloFromServlet
• Example: Discussion Group
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Discussion Group – Post New Message
View
Controller
index.html
ForumServlet
Model
Message
Bean
postform.jsp
Message
Table
postconfirm.jsp
Database
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JSP pages
HTML documents
image files
app-name
JSP pages
HTML documents
image files
Content
directories
WEB-INF
JSP and Servlet
Deployment
web.xml
Create this JSP
web application
directory
structure
Class files
classes
Class files
Package
directories
lib
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JAR files
Adapted from [Fields, Kolb]
114
Servlet Configuration
• Web application configuration file: web.xml
– Stored in WEB-INF directory
– Identifies servlets and initialization parameters
– Minimal example:
<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE web-app
PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN“
"http://java.sun.com/j2ee/dtds/web-app_2.2.dtd">
<web-app>
</web-app>
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Web.xml: Optional Elements
<display-name>
SIGAda 2001 Tutorial
</display-name>
<description>
Examples and source code for
tutorial presentation
</description>
<welcome-file-list>
<welcome-file>
index.html
</welcome-file>
</welcome-file-list>
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Web.xml: Servlet Identification
<servlet>
<servlet-name>
helloservlet
</servlet-name>
<servlet-class>
helloservlet$typ
</servlet-class>
</servlet>
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Web.xml: Servlet Mapping
<servlet-mapping>
<servlet-name>
helloservlet
</servlet-name>
<url-pattern>
/helloservlet
</url-pattern >
</servlet-mapping>
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Web.xml: Example
• SIGAda 2001 Tutorial
–
–
–
–
Hello Servlet
Hello from Servlet
Forum Servlet
Java Servlet
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Tomcat Server Configuration
• Configure Tomcat to recognize the application we
just created: TOMCAT_HOME\conf\server.xml
<Context
path="/sigada2001"
docBase="C:\JSP\Tutorial\app"
crossContext="false"
debug="0"
reloadable="true"
trusted="false" >
</Context>
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Negatives of JSP
• JSP code does not appear in browser
– Harder to debug
• Complexity of edit-transform-compile-loadrun cycle
– Need javac compiler in production machine
– Left-over compilation “crud”
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Negatives of JSP
• Error handling
– Different types of errors from transformcompile-load phases of development cycle
– JSP pages don’t easily catch certain errors such
as OutofMemoryError
– Mysterious errors: CastClassException
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An Alternative – Velocity
• Velocity is a Java-based template engine
• One of the subprojects of Jakarta Apache
• Does not embed Java code in web pages,
but uses the Velocity Template Language
• Uses a simple model of a Context (a hash
table) for passing information between web
pages and Java code
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Velocity
• Can also be used as a general-purpose
template engine, not just for web pages
• Example: Discussion Group
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More to Learn
• How to use JAR files
• How to use Java packages as subdirectories
• Handling Java exceptions
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