Enterprise Java Bean Technology BriefingMarkus Hebach

Agenda

The Need for a Server Side Component Model EJB 1.0 Architecture Overview Where does CORBA fit in? The Inprise EJB Solution - “Kodiak”

The Need for a Server Side The Need for a Server Side Component ModelComponent Model

Distributed TX’s

Security

Authorization

Data Access

Legacy Integration

Developing a Distributed Object

BusinessLogic

Business Logic Developer

=

Afte

r Tax

Ope

ratin

g Ca

sh F

low P/E Ratio

CF = (R - O)(1 - T) + Dep(T) - NWC

Net Present Value

Holding Period Returns Salil “Number Crunch” Deshpande

System Developer

=

Distributed Transactions

Persistence

Auth

entic

atio

n

Authorization

Concurrency

Geoff “Codermaniac” Bullen

Productive Distributed Developer???

BusinessLogic

Security

Distributed TX’s

Data Access

Legacy Integration

Authorization

=

EJB Acknowledges “Roles”

Bean Provider Assembler Deployer Sys Admin

Logic DeveloperNo Transaction CodeNo Concurrency CodeNo Security CodeNo Distribution of Beans

Composes ApplicationsGenerally Understands LogicExpert at Apps, Applets Servlets etc..Usually builds GUI

Deployment to Operational EnvironmentDefines Security RolesDefines TransactionsA Systems Expert

System ManagerKeeps System OperationalTypically a good cardplayer

The EJB Development Flow

JBuilderJBuilder

EJB EJB EJB

JBuilderJBuilder Servlet

HTMLJSP

EJB Server

EJB

EJB Server

EJB

HTMLJSP Servlet

EJB Architecture & Roles

EJB Server

Client AppClient App

EJBEJB

ContainerContainerEJBEJB

Bean Provider

EJB Server Provider

Assembler

Deployer

System Admin

EJB Architecture OverviewEJB Architecture Overview

Enterprise Java Beans

“The Enterprise Java Beans Architecture

is a component architecture for the development

and deployment of object oriented distributed

enterprise-level applications”.

- Sun Microsystems EJB 1.0 Specification March 1998

Responsibilities of the Container

Proper creation, initialization, and removal of beans Ensuring that methods run in the proper transaction context Visibility of the home object in a JNDI-accessible namespace Swapping to and from secondary storage (for session beans) Persistence management (for container managed entity

beans) Availability of a home object implementing creation and

lookup services Implementation of certain basic security services

Identifying an EJB

EJB (ejb-jar)

EJB Home EJB Remote

Bean Instance

Deployment Descriptor

Bean Architecture

EJB HomeEJB Home

Bean InstanceBean Instance

RemoteRemoteInterfaceInterface

Cont

aine

r

EJB Home

The Home Interface contains the signatures of the creation methods for the given bean. Each Create

method must have a corresponding ejbCreate method in the bean. Remember - Only the container can actually

create the instances!

public interface myHome extends EJBHome { public myObject create() throws RemoteException; public myObject create(String str) throws RemoteException;}

EJB Remote

In a similar fashion, the developer must create a “Remote Interface” which describes thebusiness methods (signatures) of the bean that the developer would like the client to have access to.

public interface Account extends javax.ejb.EJBObject { public void deposit(double amount) throws RemoteException; public void withdraw(double amount)throws RemoteException; public double balance() throws RemoteException;}

EJB Object

The methods in your bean will NEVER be invoked directly from the client.

The client calls the bean’s methods indirectly through the EJBObject, which acts as a proxy.

public interface javax.ejb.EJBObject extends java.rmi.Remote { public EJBHome getEJBHome() throws RemoteException; public Object getPrimaryKey() throws RemoteException; public Handle getHandle() throws RemoteException; public void remove() throws RemoteException, public boolean isIdentical(EJBObject other) throws RemoteException;}

Bean Types

Session Beans (Required for EJB 1.0)Entity Beans (Optional for EJB 1.0)

Types differentiated by Interface implemented and by the type declaration in the deployment descriptor.

Bean Types

Session Beans Execute on behalf of single client Can be transaction aware Does not represent directly shared data in a database Are relatively short lived Are removed when the EJB server crashes

Bean Types

Entity BeansRepresents data in a databaseAre transactionalAllows shared access by multiple usersSurvives crash of EJB server

Session Bean Types

Stateless SessionThe bean does not contain conversational state between method invocations - as a consequence any session bean instance can be used for any client. Stateless beans are designed to be pooled.

Session Bean Types

Stateful Session The bean contains conversational state which is kept across method invocations and transactions. Once a client has obtained a specific session bean it must use this instance for the life of the session.

EJB Server

Clients View of Session Bean

EJB Container

Thin ClientThin Client

WindowsWindowsClientClient

JavaJavaClientClient

BrowserBrowserClientClient

MobileMobileClientClient

Cart

CartHomeCartBean

JNDI

CartHome cartHome = javax.rmi.Portable RemoteObject.narrow( initialContext.lookup(...), CartHome.class); Cart cart = cartHome.create(…);

cart.addItem(66);cart.addItem(22);cart.purchase()cart.remove()

Entity Bean Types

Bean Managed PersistenceThe entity bean implementation is responsible for implementing persistence. The bean provider writes the code to access the underlying database or application. These calls are placed in the methods ejbCreate(), ejbFind(), ejbRemove(), ejbLoad() and ejbStore().

Entity Bean Types

Container Managed PersistenceThe container is responsible for implementing the persistence. Instead of the bean provider implementing the database access code, the container is responsible for generating the appropriate code and its execution. The fields of the entity bean, which are managed by the container are specified in the deployment descriptor.

EJB Server

DB

Session Bean Interacting with Entity Bean

EJB Container

Thin ClientThin Client

WindowsWindowsClientClient

JavaJavaClientClient

BrowserBrowserClientClient

MobileMobileClientClient

Cart CartBean

JNDI

OrderHome

OrderOrderBean

order.findByPrimaryKey(orderNo);

SQL

ejbLoad();placeOrder();orderComplete();

ejbStore();

The Session Bean Interface

package javax.ejb;public interface SessionBean extends EnterpriseBean { void setSessionContext(SessionContext s) throws

RemoteException; void ejbRemove() throws RemoteException; void ejbActivate() throws RemoteException; void ejbPassivate() throws RemoteException;}

package javax.ejb;public interface EntityBean extends EnterpriseBean { void setEntityContext(EntityContext e) throws RemoteException; void unsetEntityContext() throws RemoteException; void ejbRemove() throws RemoteException; void ejbActivate() throws RemoteException; void ejbPassivate() throws RemoteException; void ejbLoad() throws RemoteException; void ejbStore() throws RemoteException;}

The Entity Bean Interface

Holes in the EJB 1.0 Specification

No definition of Interoperability between containers. Does not prescribe which RMI implementation should

be used. No definition for propagating Transaction Contexts No recommendations for bridging security domains No standard Container API

Where does CORBA fit in?Where does CORBA fit in?

The role of CORBA in EJB

“The Enterprise Java Beans Architecture

will be compatible with CORBA.

- EJB 1.0 Specification Section 2.1 Overall Goals

EJB 1.0 Section 4.4 Standard CORBA Mapping

“To ensure interoperability for multi-vendor environments, we define a standard mapping of the Enterprise JavaBean client’s view contract to CORBA.”

The mapping to CORBA covers:1. Mapping of the EJB Client interfaces to CORBA IDL2. Propagation of transaction context3. Propagation of security context

Results of the CORBA Mapping

On the wire interoperability between EJB Servers from multiple vendors.

Enables non-Java clients to access EJB’s. CORBA Object Services allow security and transactions

to be handled in a distributed vendor independent manner.

“Open” implementation choices

RMI/IIOPJNDI over COSNaming and/or LDAPJTS/COSTransactions and IIOPX.509 certificates/IIOP over SSL

The Inprise EJB Solution “Kodiak”The Inprise EJB Solution “Kodiak”

Inprise EJB Infrastructure

Language Independent ClientLanguage Independent ClientATMATMSessionSession

BeanBean

Java DBJava DBJTSJTS

2 Phase 2 Phase CommitCommit

JNDIJNDINamingNamingContainerContainerAcctAcct

EntityEntityBeanBean

Database

RMI/IIOP CosNaming

LDAP

CosTransactionsDistributed

2 Phase Commit

CORBA 2.3Objects By Value

Can generate IDL from the Home andRemote Interfaces.

IIOP/SSLAccess Control

Complete Java Database

Inprise EJB Server Operation Modes

Development Mode All services will run together in a single process JNDI/Lightweight Naming Service Lightweight JTS Implementation All Java Database for Container Managed Persistence

Operations Mode Fully Distributed Service JNDI/COSNaming ITS/COSTransaction implementation

A Fully Distributed EJB Solution

ContainerContainer

ContainerContainer

JNDIJNDINamingNaming

StorageStorage

JTS/ITSJTS/ITS

JTS/ITSJTS/ITS

Distributed TransactionsDistributed Security Domains

Language Interoperability