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CSE298
CSE300
Java Beans and
Enterprise Java Beans
Paul C. Barr
The Mitre Corporation
Eatontown NJ
Kimble Cheron,
Prof. Steven A. Demurjian,
and Mitch Saba
Computer Science & Engr. Dept.
[email protected]
[email protected]
http://www.engr.uconn.edu/~steve
(860) 486 - 4818
JR&B-1.1
CSE298
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Changing Perspectives
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Computers are Guilty of Creating More Disorder
then Simplicity
Current Software Systems are Relics
 Built Largely By and For Technical Computer
Users
 Never Intended to Operate in Today’s
Environment
Designer’s Need to Break Out of Old Mold
 Consider Total Design Space
 Design Should Help Manage Complexity, Not
Add to It
What is Available to Assist in Changing Times?
JR&B-1.2
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Components

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Reusable Software Building Blocks
Pre-Constructed from Encapsulated Application
Code
 Easily Combined with Other Components
 Seamlessly Merged with Custom Code
 Rapid Prototyping of Complete Applicaiton
What is a Component?
 GUI Widget (Button, Window, etc.)
 Combination of Components (Window with
Elevator Bars and Pull-Down Menus)
 Application Service (Account Management
Function)
JR&B-1.3
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Overview

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A First Look at Java Beans
 What are They?
 How are They Utilized?
Enterprise Java Beans
 Not Just for Clients Anymore!
 Capabilities and Usage
 Relationship to “New” and “Old” Technologies
 Component-Based Client/Server Model
Multi-Tiered Architecture and EJB
 Tiered Development for Extensibility
 Comparisons of Approaches
Java Blend for Database Interoperability
JR&B-1.4
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Java Beans


Extends "Write Once, Run Anywhere (WORA)TM"
to Include "Reuse Everywhere”
What is a Bean?
 Independent Reusable Software Component
 Visually Manipulated in Builder Tools
 Can Be Visible Object:
 AWT Components

or Invisible Objects:
 Queues and Stacks

or Composed Objects:
 Calculator Ops + Keys + Display
JR&B-1.5
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Java Beans

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Bean vs. Component
 Source Code Inaccessible
 Customizable to Suit Application Needs via
External Properties
 Powerful Means of Reuse
Examples
 GUI Button with Property to Allow Button
Name to be Set
 Account Management Component that Allows
Account Database Location to be Set
Properties Can be Very Complex and Offer
Significant Power to Application Builders
JR&B-1.6
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Java Beans Fundamentals


Supported within IDEs
 Visual Age, JBuilder, PowerJ, Visual Café
 Construct JavaBeans Component as Specialized
Java Classes with Enhanced Capabilities
Three-Part Architecture
 Events
 Notifies Others When Something Has Occurred
 Delegation-Event Model of AWT

Properties
 Define the Characteristics of the Bean

Methods
 Utilized to Define a Property
JR&B-1.7
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Architecture: Events
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Events
 Notifies Others When Something Has Occurred
 Delegation-Event Model of AWT
Event Elements
 Eventobjects
 Components Sends to Listener

Eventlisteners
 In Order to Register an Eventlistener With a
Component, the Component Must Understand the
Event Set
Event Sources
We’ll Discuss Shortly and Revisit in Detail with
Java RMI


JR&B-1.8
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Architecture: Properties
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Example: AWT Textfield
 User Will See Properties for the Caret Position,
Current Text, and the Echo Character, etc.
Methods Used to Define a Property
public void setPropertyName(PropertyType value);
public PropertyType getPropertyName();
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The Name of the Property is Propertyname
The Datatype is Propertytype
Only One Method Present the Property is ReadOnly (Set Missing)
Or the Property is Write-only (Get Missing)
JR&B-1.9
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Architecture: Methods
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Methods
 Public
 Available for Anyone to Call

Beaninfo and Getmethoddescriptors Method
 Restricts Which Methods Are Visible to the
Beanbuilder/Integration Tool


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The Getmethoddescriptors Method Reports All
the Methods of a Bean
Supports Introspection
Beaninfoclass
 Customize a Bean's Appearance to an Integration
Tool
JR&B-1.10
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Abilitiy

Persistence
 Ability of an Object to Store its State
 Object Serialization Saves All Non-static and
Non-transient Instance Variables of an Object
 Objectinput and Objectoutput Interfaces
 The Basis for Serialization Within Java.

Objectinputstream and Objectoutputstream
Classes
 Implement the Objectinput and Objectoutput
Interfaces
JR&B-1.11
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Five Defining Features
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Introspection
 Allow a Builder Tool to Analyze How a Bean
Works
Customization
 User is Allowed to Alter the Appearance and
Behavior of a Bean
Events
 Firing of Events
 Inform Builder Tools About Both the Events
They Can Fire and Handle
JR&B-1.12
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Five Defining Features
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Properties
 Beans Can Be Manipulated Programmatically
 Support the Customization as Mentioned
Persistence
 Customized Beans Can Have Their State Saved
and Restored
 Work in a Constructed Application Can Be
Restored by an Application Builder's Save and
Load Menu Commands
Beans Are Used Primarily With Builder Tools
 Programmatic Interfaces Allow Beans to Be
Manually Manipulated by Text Tools
JR&B-1.13
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Differences Between Beans and Classes
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Introspection
 Process of Determining the Supported
Properties, Methods, and Events of a Bean
Introspector Class
 Provides Access to the Beaninfo for the Bean
Component Via Its getBeanInfo Method
 Code
TextField tf = new TextField ();
BeanInfo bi = Introspector.getBeanInfo
(tf.getClass());

Alternative to Introspector Class
 Provides Access Directly Through the Use of
the Reflection API
JR&B-1.14
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Introspection Tools
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Differentiates Beans From Typical Java Classes
Recognize Predefined Patterns in Class Definitions
and Method Signatures
 Able to "Look Inside" a Bean to Determine Its
Properties and Behavior
Require That Method Signatures Within Beans
Must Follow a Certain Pattern
Recognize How Beans Can Be Manipulated at
Design and Run Time
Pattern Signatures are Designed to Be Recognized
by Human Readers and Builder Tools
JR&B-1.15
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Bean vs. Class
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A Bean's State Can Be Manipulated at Design Time
in Contrast to Classes at Run Time
Beans Attributes and Behaviors
 Published by Special Method Signature Patterns
 Recognized by Beans-Aware Application
Construction Tools
What to Use for Software Modules?
 Beans are Better for Software Components
Visually Manipulated Within Builder Tools
 Classes are Better for Functionality Through a
Programmatic (Textual) Interface
 An SQL API Would Be Better Packaged Through a
Class Library
JR&B-1.16
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Event Model
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Three Elements
 Eventobject
 Eventlistener
 Eventsource (the Bean)
Eventobject
 Basis of All Beans Events
 Java.Util.Eventobject Class
 Require Programmer to Subclass an
Eventobject to Have a Specific Event Type
JR&B-1.17
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Java 1.1 Delegation Event Model
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Example: Event for Employee’s Hire Date
public class HireEvent extends EventObject {
private long hireDate;
public HireEvent (Object source) {
super (source);
hireDate = System.currentTimeMillis();
}
public HireEvent (Object source, long
hired) {
super (source);
hireDate = hired;
}
public long getHireDate () {
return hireDate;
}
}
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EventListener

Definition
 Entity That Desires Notification When an Event
Happens
 Receives the Specific Eventobject Subclass As
a Parameter
JR&B-1.20
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EventListener

Eventlistener Interface
 Empty Interface
 Acts as a Tagging Interface That All Event
Listeners Must Extend
 Eventtypelistener Name of Listener Interface
 The Name for the New Hireevent
Listener Would Be Hirelistener
 Method Names Should Describe the Event
Happening
 Code
public interface HireListener
extends java.util.EventListener {
public abstract void hired (HireEvent e);
}
JR&B-1.21
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EventSource

Eventsource
 Defines When and Where an Event Will
Happen
 Hireevent and Hirelistener Are Required for an
Event Source to Function
 Sends Notification to Registered Classes When
the Event Happens
JR&B-1.22
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EventSource: Methods

Registration Process Method Patterns
public synchronized void
addListenerType(ListenerType l);
public synchronized void
removeListenerType(ListenerType l);

Maintaining Eventsource Code
private Vector hireListeners = new Vector();
public synchronized void
addHireListener(HireListener l) {
hireListeners.addElement (l);
}
public synchronized void
removeHireListener (HireListener l) {
hireListeners.removeElement (l);
}
JR&B-1.23
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EventSource: Hiring Example
protected void notifyHired () {
Vector l;
// Create Event
HireEvent h = new HireEvent (this);
// Copy listener vector so it won't change while
firing
synchronized (this) {
l = (Vector)hireListeners.clone();
}
for (int i=0;i<l.size();i++) {
HireListener hl = (HireListener)l.elementAt (i);
hl.hired(h);
}
}
JR&B-1.24
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What is Enterprise Java Beans ?
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Expansion of Java Beans (Client-side) to Support
Server Side Reusable Components
 Server Components Run on Application Server
 EJB Integral Part of Java Technology
Component Architecture for Distributed Systems
 Multi-Tier Distributed Architecture
 Movement of Application Logic from Client to
Server Side
 Creation of “Thin”, Easier to Maintain Clients
Framework for Creating Middle Ware
 Integration of “New” and “Old” Technologies
 RMI, IIOP, CORBA, RPC, Active X, etc.
JR&B-1.25
Designer and Developer Roles in
Enterprise Java Beans (EJB)
CSE298
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Towards “Highly Scalable, Highly Available,
Highly Reliable, Highly Secure, Transaction
Distributed Applications”
Enterprise Bean Provider
 Creates and Sells EJBs
Application Assembler
 Uses EJBs to Build an Application
EJB Server Provider
 Creates and Sells EJB Server
EJB Container Provider
 Creates and Sells EJB Containers
 Server Provider Will Likely Provide Containers
JR&B-1.26
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EJB Roles & Deployment
JR&B-1.27
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Utilizing EJB Technology
JR&B-1.28
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The EJB Architecture
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EJB Servers: Analogous to CORBA ORB
 Server Software
 Provides Naming and Transaction Services
 Makes Containers Visible
EJB Containers: Interface Between EJB Bean and
Outside World
 Client Never Accesses Bean Directly
 Access via Container-Generated Methods
 These Methods Then Call the Bean’s Methods
EJB Clients
 Locate EJB Containers Via JNDI
 Make Use of EJB Beans
Enterprise Java Beans - Discussed Shortly
JR&B-1.29
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Recall CORBA
JR&B-1.30
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EJB Container
JR&B-1.31
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Enterprise Java APIs
JR&B-1.32
Enterprise Java Beans
Session Beans
CSE298
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Associated With a Particular Client
Performs Operations on Behalf of Client
 Accessing a Database
 Performing Calculations
Created and Destroyed by a Client
Can be Transactional - But, Do Not Survive
System Shutdown
Can be Stateless or Maintain Conventional State
Across Methods and Transactions
Must Manage Own Persistent Data
JR&B-1.33
Enterprise Java Beans
Entity Beans
CSE298
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Object Representation of Persistent Data
Maintained in Permanent Store (Database
Identifiable by Primary Key
Shared by Multiple Clients
Persist Across Multiple Invocations
Survive System Shutdown
Created by
 Inserting Data into Database
 Creating an Object Instance
JR&B-1.34
Model for Persistence
Passivation/Activation
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Programmatic Model for Managing Persistent
Objects
EJB Server has the Right to Manage its Working
Set
Passivation
 Saves State of a Bean to Persistent Storage
 Then Swaps Bean Out
Activation
 Restores State of a Bean From Persistent
 Storage,Then Swaps Bean in
Applies to Both Session and Entity Beans
JR&B-1.35
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Stateless vs. Stateful Session Beans
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Stateless
 No Internal State
 Do Not Need to Be "Pass-ivated"
 Can Be Pooled to Service Multiple Clients
Stateful
 Possess Internal State
 Need to Handle Passivation/Activation
 One Per Client
JR&B-1.36
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Persistent Session Beans
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Session Beans Can Be Saved and Restored Across
Client Sessions
To Save
 Call the Session Bean’s getHandle() Method
 Returns a Handle Object
To Restore
 Call the Handle Object’s getEJBObject()
Method
JR&B-1.37
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Entity Bean Persistence
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Container-Managed
 Container is Responsible for Saving State
 In Deployment Descriptor, Specify ContainerManaged Fields
 Persistence Independent of Data Source
Bean-Managed
 Bean is Responsible for Saving its Own State
 Container Doesn’t Need to Generate DB Calls
 Less Adaptable; Persistence is Hard-Coded
JR&B-1.38
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Writing an EJB Client
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Locate the Bean Container
Allocate a Bean, If Needed
Use the Bean
Dispose of the Bean
//An idealized EJB client
import paul.ejb.restaurant.*;
public class EJBClient{
public static void main(String[] argv){
//get JNDI naming context
javax.naming.Context initialContext = new
javax.naming.InitialContext();
//use context to look up EJB home interface
RestaurantHome rh = initialContext.lookup(“RestaurantHome”);
//use home interface to create a session object
Restaurant r = rh.Create(“Burger Heaven”);
//invoke business methods
r.order(“cheeseburger”);
//remove session object
r.remove();
}
}
JR&B-1.39
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Writing a Session Bean
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Create Remote Interface
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Create Home Interface
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must extend javax.ejb.EJBHome interface

create() methods, remove() methods
Implement Create Methods

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must extend javax.ejb.EJBObject interface
must give prototypes for business methods
class needn’t say “implements”; this is handled by the container
called by container at creation time
Implement the SessionBean Interface


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ejbActivate() - called when bean is activated
ejbPassivate() - called when bean is passivated
ejbRemove() - called when bean is destroyed
setSessionContext(SessionContext ctx) - called by container to give bean
a context
JR&B-1.40
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Session Bean Example
package paul.ejb.restaurant.server;
public class OrderBean implements SessionBean{
private transient SessionContext ctx;
private String order;
//can have many create methods
public void ejbCreate () throws Exception {
//initialization of class variables here
}
//business method
public boolean order(String order) {
this.order = order;
System.out.println("order received for " + order);
return true;
}
//these methods are required by the SessionBean interface
public void ejbActivate() throws Exception {
}
public void ejbDestroy() throws Exception {
}
public void ejbPassivate() throws Exception {
}
public void setSessionContext(SessionContext ctx) throws
Exception {
this.ctx = ctx;
}
}
JR&B-1.41
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Writing an Entity Bean

Implement the EntityBean Interface

ejbActivate() // called on activation
ejbPassivate() // called on passivation
ejbLoad() // tells bean to load state from database
ejbStore() // tells bean to store state in database
ejbRemove() // called when client calls remove()
setEntityContext() // called by container when instance has been created
unsetEntityContext() // called by container before removing the instance

must also implement ejbFind() // allows client to look up EJB objects

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Optionally Implement create() Methods
Create Remote Interface
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must extend javax.ejb.EJBObject interface
Create Home Interface
JR&B-1.42
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Entity Bean Example
package paul.ejb.entity.server;
public class ExampleBean implements EntityBean
{
private transient EntityContext ctx;
//notice: no finder method -- generated at deployment time by container provider
//can have multiple create methods
public void ejbCreate () throws Exception {
}
//business method
public boolean doSomething () {
}
//required methods for EntityBean interface
public void ejbActivate() throws Exception {
}
public void ejbDestroy() throws Exception {
}
public void ejbPassivate() throws Exception {
}
public void ejbLoad() throws Exception {
}
public void ejbStore() throws Exception {
}
public void setEntityContext (EntityContext ctx) throws Exception {
this.ctx = ctx;
}
JR&B-1.43
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Deploying EJBs
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EJBs Deployed As .SER Files: Serialized Instance
Manifest File Used to List EJBs
Must Also Provide a “Deployment Descriptor”
Sample Entry
 Name: paul.RestaurantDeployment.ser
 Enterprise-Bean: True
“Name” Line
 Describes a Serialized Deployment Descriptor
“Enterprise-Bean” Line
 Indicates Whether the Entry Should Be Treated
as an EJB
 (Not All Entries Need to Be EJBs)
JR&B-1.44
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Who’s Announced EJB Support?
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WebLogic
IBM
Oracle
GemStone
BEA
Borland
Netscape
Lotus
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Forte
Progress
Novell
Novera
Borland
Informix
IONA
More...
JR&B-1.45
Typical Development and Deployment
Scenario
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EJB Server Provider
 Creates and Sells an EJB Server
 Provides EJB Containers That Will Run on
These Servers
EJB Providers
 Individuals Responsible for Developing the
EJBs
 Provide “Tools” and “Components” for DownStream Usage
Application Assemblers
 Individuals that Utilize Pre-Built EJBs to
Construct Their Domain-Specific Applications
 Utilize “State-of-Art-Tools” for EJB and JB
JR&B-1.46
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EJB Component-Based Architecture
EJB Server
EJB Client
Invoke EJB
Container
Methods
Enterprise
Java Bean
Invoke
EJB
Methods
EJB Container
JR&B-1.47
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Client-Server Component Model
JR&B-1.48
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Client-Server Component Relationship
JR&B-1.49
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Client-Server Component Relationship
(Concluded)
JR&B-1.50
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EJB Server Example
JR&B-1.51
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EJB Server Example (continued)
JR&B-1.52
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EJB Server Example (Concluded)
JR&B-1.53
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Three-Tier Architecture Concept
JR&B-1.54
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Two-Tier, Three-Tier, Four-Tier
Example Architectures
From: http://java.sun.com/javaone/javaone98/sessions/T400/index.html
JR&B-1.55
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Wombat Securities
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Web Access to Brokerage Accounts
Only HTML Browser Required on Front End
"Brokerbean" EJB Provides Business Logic
Login, Query, Trade Servlets Call Brokerbean
Use JNDI to Find EJBs, RMI to Invoke Them
Order and History Records from Java Blend
Product
Records Mapped to Oracle Tables, JDBC Calls
JR&B-1.56
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Four-Tier Architecture Example
JR&B-1.57
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Initialization Code
class LoginServlet extends HttpServlet {
private Broker createBroker(String account, String password) {
/* Use JNDI to find Broker EJB home, then return new EJB */
Context initialContext = new InitialContext();
BrokerHome brokerHome = (BrokerHome)
initialContext.lookup("wombat/Broker");
return brokerHome.create(account, password);
}
public doPost
(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
/* Get account and password from HTML and create EJB*/
String account = req.getParameter("Account");
String password = req.getParameter("Password");
Broker brk = createBroker(account, password);
...}
...}
JR&B-1.58
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User Interface Code
class TradeServlet extends HttpServlet {
...
public void doPost(HttpServletRequest req,
HttpServletResponse res) throws ServletException {
/* Get parameters from HTML and session object */
HttpSession session = req.getSession(true);
String ticker = req.getParameter("Symbol"); ...
Broker brk = (Broker)
session.getValue("LoginServlet.BrokerRef");
/* Place order and print confirmation as HTML */
String orderNum = brk.submitOrder(txType, ticker, shares);
printOrderSubmitted(out, account, orderNum);
... }
}
JR&B-1.59
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Business Logic Code
class BrokerBean implements SessionBean {
public void ejbCreate (String account, String password) ...
public SecurityRecord getAcctPositions ( ) ...
public OrderRecord getOrderStatus ( ) ...
public String getQuote(String ticker) ...
public String submitOrder(String txType, String ticker...)
...
public HistoryRecord getAcctHistory ( ) ...
private boolean login (...) ...
... etc ...
}
JR&B-1.60
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Database Access Code

SQL:
CREATE TABLE ORDER(
ORDERNUM INTEGER NOT NULL,
CUST INTEGER NOT NULL,
TICKER VARCHAR(5), ...
PRIMARY KEY (ORDERNUM),
FOREIGN KEY (CUST) REFERENCES CUSTOMER);

Java:
class Order{
int orderNum;
Customer cust;
String ticker;
...}

Java Blend Automatically Maps Classes to/from
Relational Tables at Compile-Time and Run-Time
JR&B-1.61
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Nocturnal Aviation, Inc.
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Passenger Check-in for Regional Airline
Local Database for Seating on Today's Flights
Clients Invoke EJBs at Local Site Through RMI
EJBs Update Database and Queue Updates
JMS Queues Updates to Legacy System
DBC API Used to Access Local Database
JTS Synchs Remote Queue With Local Updates
JR&B-1.62
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Three-Tier Example
JR&B-1.63
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Santa Cruz Widgets
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Small Manufacturer Previously on C++
New Order Entry, Inventory, and Invoicing
Applications in Java Programming Language
Existing Customer and Order Database
Most of Business Logic in Stored Procedures
Tool-generated GUI Forms for Java Objects
Located Company on Web Using Widgets and Tcl,
but Not Widgets and Java
JR&B-1.64
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Santa Cruz Widgets (2-tier)
JR&B-1.65
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Architecture Comparisons
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Two-tier Through JDBC API: Simplest
Multi-tier: Separate Business Logic, Protect
Database Integrity, More Scaleable
JMS Queues Vs Synchronous (RMI or IDL):
 Availability, Response Time, Decoupling
JMS Publish & Subscribe: Off-line Notification
RMI IIOP Vs JRMP Vs Java IDL:
 Standard Cross-language Calls or Full Java
Functionality
JTS: Distributed Integrity, Lockstep Actions
JR&B-1.66
CSE298
CSE300
Further API Comparisons
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Servlets: Simplifies HTML, Connections, Web
Front-Ending Legacy Systems
EJBs: Simplifies Components, Scalability,
Transactions, Multi-threading, Security, State
JDBC Vs ODMG Vs SQLJ API:
 Programming Simplicity, Portability, SQL
Knowledge
JNDI: Standardized Name Service Access
Enterprise Java APIs vs. Proprietary:
 Multi-Platform, Multiple Providers
JR&B-1.67
CSE298
CSE300
Summary & Key Messages
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Enterprise Java APIs: EJB, JNDI, Java IDL, RMI,
JDBC, ODMG, SQLJ, JMS, JTS, JMAPI, Servlets
Wide Variety of Architectural Alternatives:
 Synchronous/Asynchronous, Multi-Tier,
Transactional, HTTP/JRMP/IIOP
Benefits:
 WORA Portability
 Multiple Vendors
 Legacy Connectivity
 Java Programming Language Productivity
JR&B-1.68
CSE298
CSE300
EJB Roadmap
API
Specification
Complete
Products
EJB
JNDI
JIDL
RMI
JDBC
ODMG
SQLJ
JMS
JTS
JMAPI
Sevlets
JavaSoft
JavaSoft
OMG
JavaSoft
JavaSoft
Consortium
Consortium
JavaSoft
OMG
JavaSoft
JavaSoft
1.0Q1
1.0 done
1.0 Q2
1.0 done
2.0 Q2
2.0 done
1.0 Q2
1.0 Q2
1.0 done
1.0 Q2
1.1 done
See Partners
Download SP
JDK 1.2
JDK 1.1
JDK 1.2 Partner
JavaBlend
See Partners
See Partners
Partners
See Partners
Java Web Server
JR&B-1.69
CSE298
CSE300
What Is the Java Blend Product?



Product That Integrates Java Programming
Language Objects With Enterprise Data
Provides a Single Object Model Based on Java
Programming Language Classes
 Automatic Persistent Storage for Java
Application Objects
 Easy, Automatic Access to Existing Relational
Databases From Java Applications
Result of Joint Development by the Javasoft
Division, Baan and Tech@spree
JR&B-1.70
CSE298
CSE300
JavaBlend Applications


JavaBlend Software Provides Mapping Capability
Between Database Tables and Java Application
Classes
Programmer Deals Only With Java Programming
Language Objects, and Does Not Need to Know
SQL or Database Representation
JR&B-1.71
CSE298
CSE300
Java Blend Components


Flexible Development Tool for Automatic
Bi-Directional Mapping
 Objects to Relational
 Relational to Objects
Powerful Runtime Environment
 Transaction Management System
 Query Processor
 Cache Management System
JR&B-1.72
CSE298
CSE300
Java Blend Runtime Architecture
JR&B-1.73
Java Blend Software and Enterprise
JavaBeans Technology
CSE298
CSE300


EJB Technology Provides Scaleable Component
Architecture for Business Applications
Java Blend Product Provides Transparent
Persistence for Enterprise Javabeans Technology
 Beans Implementing Business Logic Use Java
Blend for Database Access
 Java Blend Product Works With the Enterprise
Javabeans API Transaction Mechanisms
JR&B-1.74