Aravind Vinnakota EJB Architecture
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Transcript of Aravind Vinnakota EJB Architecture
EJB Architecture and Design
CS486 Global Knowledge Networks Instructor : Dr. V. Juggy
Presentation by: Aravind Vinnakota
What is EJB?An EJB is just a collection of Java
classes and XML file, bundled into a single unit. The Java classes must follow certain rules and provide certain callback methods.
EJB is just a specification. It is not a product.
EJBs are reusable components.
What is EJB?EJB is a widely-adopted server-side
component architecture for J2EE.EJB components are designed to
encapsulate business logic, and to protect the application developer from having to worry about system level issues.
ContentsServices provided by EJB containerCircumstances of EJB component usageHow an EJB component looks like?View of an EJB component by client
programmer and EJB developerMechanisms by which EJB container provides
its servicesRules an EJB developer must follow and how
to use EJBs in a web architecture?
Key features of EJB technology
EJB components are server-side components written entirely in the Java programming language
EJB components contain business logic only - no System-level programming
System-level services (i.e. "plumbing") such as transactions, security, Life-cycle, threading, persistence, etc. are automatically managed for the EJB component by the EJB server
Key features of EJB technology
EJB architecture is inherently transactional, distributed, portable, multi-tier, scalable and secure
EJB components are fully portable across any EJB server and any OS, work with any client.
Components are declaratively customizedThere are four major parts to every bean: the
home interface, the remote interface, the implementation class and the XML deployment descriptor
EJB vs JavaBeansThe JavaBeans architecture is meant to
provide a format for general-purpose components whereas the EJB architecture provides a format for encapsulation and management of business logic.
JavaBeans has tier of execution at Client and EJB has at Server (specifically business logic tier)
EJB vs JavaBeans In JavaBeans the runtime execution
environment provides services like Java libraries, Java application etc. The EJB runtime environment provides services of Persistence, declarative transactions and security, connection pooling and lifecycle services.
Varieties of BeansSession Beans Stateful session bean Stateless session beanEntity Beans With container-managed persistence With bean-managed persistenceMessage-Driven Beans
Why use EJBs in your design?
EJB specification provides enterprise-level services, that is, it provides software services that are fundamental to an organization’s purpose.
EJB’s API was designed to keep the application programmer from having to provide systems-level services, so that they are free to concentrate on business logic.
Why use EJBs in your design?
A requirement of any of the services provided by an EJB container like transactions, scalability, persistence, security, future growth possibilities is an appropriate reason to use EJB in the design of the application.
EJB Architecture
J2EE Application Server
EJB Container
Application Logic DataClient
RDBMS
Corba
RM
I JDB
C JavaM
ail JMSJTA
Session Bean
Entity Bean
Client Application
Roles in EJB DevelopmentEJB provider - a person who develops
EJB ComponentsEJB Deployer - a person responsible
for deploying EJB’s in EJB serverApplication Server/ EJB Container
Vendor - one who provides application server on which the application is deployed
Roles in EJB DevelopmentApplication assembler - one who
combine the EJB components with other software to make a complete application
System administrator - one who manages the application after it has been deployed into a target environment.
Roles in EJB Development
EJBProvider
ApplicationAssembler
App Server/EJB Container
Provider
Deployer
SystemAdministrator
EJB Container and its Services
A container is an execution environment for a component. The component lives in the container and the container provides the services for the component.
Similarly, a container lives in an application server, which provides an execution environment for it and other containers.
Services provided by an EJB container
Persistence Ex: simple connection pooling,
automatic persistence, etc. EJBs created with application development tools will encapsulate data access in components.
Services provided by an EJB container
Declarative transactionsData cachingDeclarative SecurityError HandlingComponent Framework for Business LogicScalability and Fall-OverPortabilityManageability
How the Container Provides Services
There are three basic ideas: First, there are clearly defined responsibilities between
the various parts of an application using EJB component namely the client, the EJB container and the EJB component. The definition of these responsibilities is formally known as a contract.
Second, the services that the container provides are defined in such a way that they are orthogonal to the component. In other words, security, persistence, transactions are separate from the Java files that implement the business logic of the component.
How the Container Provides Services
Third, the container interposes on each and every call to an EJB component so that it can provide its services. In other words, the container puts itself between the client and the component on every single business method call.
Contracts
EJB Container/Application Server
Enterprise JavaBean
Client
Rules for the bean programmer The developer of the EJB component must implement
the business methods in the implementation class The bean provider must implement the ejbCreate(),
ejbPostCreate(),ejbRemove() methods and the ejbFind<METHOD>() methods if the bean is an entity with bean managed persistence
The bean provider must define the enterprise bean’s home and remote interfaces
For session beans, the bean provider must implement the container callbacks defined in the javax.ejb.SessionBean interface
Rules for the bean programmer
For entity beans, the provider must implement the container callbacks defined in the javax.ejb.EntityBean interface
The bean provider must not use programming practices that would interfere with the container’s runtime management of the enterprise bean instances
Interposition : method call to an EJB Container from a remote client
First, the client makes a call on the RMI stub
This RMI stub interposes on the method call in order to marshal parameters and send the information across the network
A skeleton on the server side unmarshals the parameters and delivers them to the EJB Container
Interposition diagram
Interposition class
ClientContainergenerated
classEJB
RMI Stub
RMIStub
Network
Interposition : from EJB Container to EJBs The container will examine the security credentials of
the caller of the method It will start or join with any required transactions It will make any necessary calls to persistence functions It will trigger various callbacks to allow the EJB
Component to acquire resources Only after all this is done will the actual business
method be called Once it is called, the container will do some more work
with transactions, persistence, callbacks and returns data or exception to the remote client
Working with EJBs The Enterprise JavaBeans
specification is written for three audiences:
The Client developerThe EJB developerThe EJB container developer
EJB ClientsEJB Clients are applications that access EJB
components in EJB containers. There are two possible types. The first category is application clients which are stand-alone applications accessing the EJB components using the RMI-IIOP protocol. The second category of application clients are components in the web container. They are java servlets and JSPs which also access the EJB components via the RMI-IIOP protocol.
The Client Developer’s ViewThe client has a smaller set of concerns then a
bean developer with regard to using EJBs. Basically, he need to know :
how to find or create a bean, how to use its methods and how to release its resourcesThe client need not worry about the
implementation of the EJB, callbacks that the EJB container will make on the EJB or nature of the services provided to the EJB.
EJB’s interfaceHome Interface : It is primarily for the life
cycle operations of the bean: creating, finding, and removing EJBs. The home interface is not associated with a particular bean, just with a type of bean.
Remote Interface : It is for business methods. Logically, it represents a particular bean on the server. The remote interface also provides some infrastructure methods associated with a bean instance, rather than a bean type.
Sample client application pseudo code
A client programmer will acquire an EJB’s home interface through JNDI, and they use this home interface to :
Create or findinstance of bean
Execute methods Reference(Handle)
Remove bean
Client.java Package orderMgmt; import java.util.properties; import java.naming.Context; // for name-to-object findings import java.naming.InitialContext;// context for naming operations public class Client { try { Properties prop = new Properties(); // server dependent properties for InitialContext prop.put(Context.INITIAL_CONTEXT_FACTORY,
“org.jnp.interfaces.NamingContextFactory”); prop.put(Context.PROVIDER_URL, “localhost:1099”); Context ctx = new InitialContext(prop); Object objref = ctx.lookup(“OrderManagement”);
Client contd.. // casting home interface reference to the OrderManagementHome OrderManagementHome home = (OrderManagementHome)
javax.rmi.PortableRemoteObject.narrow(objref, OrderManagementHome.class);
// home interface to create an instance of the OrderManagement OrderManagement orderManagement = home.create(); // calling placeOrder() orderManagement.placeOrder("Dan OConnor", "Wrox books on programming", 1000); orderManagement.remove(); System.out.println("Order successfully placed."); } catch (Exception e) { e.printStackTrace(); } } }
The Bean Programmer’s viewMain responsibility is write business logic and
structure the code in a particular structure. The structure has 4 files, the home interface, remote interface, business logic class file and the XML file. The XML file called the deployment descriptor, contains the structural information about the bean, declares the bean’s external dependencies and specifies certain information about how services such as transaction and security work.
Interface EJBObject package javax.ejb; public interface javax.ejb.EJBObject extends
java.rmi.Remote { EJBHome getEJBHome() throws java.rmi.RemoteException; Handle getHandle() throws java.rmi.RemoteException; Object getPrimaryKey() throws java.rmi.RemoteException; boolean isIdentical(EJBObject obj) throws
java.rmi.RemoteException; void remove() throws java.rmi.RemoteException; }
OrderManagement code.. package orderMgmt; import javax.ejb.*;
public interface OrderManagement extends javax.ejb.EJBObject { public void placeOrder(String custName, String prodName, int
quantity) throws java.rmi.RemoteException; public void cancelOrder(String custName, String prodName) throws java.rmi.RemoteException; public boolean isShipped(String custName, String prodName)
throws java.rmi.RemoteException; }
OrderManagementBean code.. package orderMgmt; import javax.ejb.*;
public class OrderManagementEJB implements javax.ejb.SessionBean { public void placeOrder(String custName, String prodName, int
quantity) { // ... Business logic ...} public void cancelOrder(String custName, String prodName) { // ... Business logic ...} public boolean isShipped(String custName, String prodName) { // ... Business logic … return true; }
OrderManagementBean code.. public void ejbCreate() { // Can be empty } public void ejbRemove() { // Can be empty } public void ejbActivate() { // Can be empty} public void ejbPassivate() { // Can be empty} public void setSessionContext( SessionContext ctx ) { // Can be empty} }
Interface EJBHome Package javax.ejb; public interface EJBHome extends java.rmi.Remote { EJBMetaData getEJBMetaData () throws
java.rmi.RemoteException; HomeHandle getHomeHandle() throws
java.rmi.RemoteException; void remove(Handle handle) throws
java.rmi.RemoteException, java.ejb.RemoveException; void remove(Object primary key) throws
java.rmi.RemoteException, java.ejb.RemoveException; }
OrderManagementHome code..
package orderMgmt; import javax.ejb.*;
public interface OrderManagementHome extends javax.ejb.EJBHome
{ public OrderManagement create() throws java.rmi.RemoteException,
javax.ejb.CreateException; }
The xml file : ejb-jar.xml <?xml version=“1.0”?> <ejb-jar> <enterprise-beans> <session> <ejb-name>OrderManagement</ejb-name> <home>orderMgmt.OrderManagementHome</home> <remote>orderMgmt.OrderManagement</remote> <ejb-class>orderMgmt.OrderManagementBean</ejb-class> <session-type>Stateless</session-type> <transaction-type>Container</transaction-type> </session> </enterprise-beans>
The xml file : ejb-jar.xml <assembly-descriptor> <container-transaction> <method> <ejb-name>OrderManagement</ejb-name> <method-name>*</method-name> </method> <trans-attribute>Required</trans-attribute> </container-transaction> </assembly-descriptor> </ejb-jar>
Structure of JAR file META -INF\ ejb-jar.xml orderMgmt\ OrderManagement.class OrderManagementHome.class
OrderManagementBean.class
What you can’t do in an EJB component?
You cannot use Reflection API to access information inaccessible to you.
You cannot create a class loader or replace a security manager.
You cannot set the socket factory used by ServerSocket or Socket
You cannot use the object substitution features of the serialization protocol
What you can’t do in an EJB component?
use Threads or the Threading APIuse the AWTAct as a Network Serveruse Read/Write static fieldsuse java.io packageLoad a native libraryuse “this” as an Argument or Return valueuse Loopback Calls
EJB Components on the Web Three classes of objects in MVC architecture:Model : This is the data and business-logic
component. It can serve multiple views.View : This is the presentation component or
the user-interface component. There can be different presentations of a single model.
Controller : This is the component that responds to user input. Translates user-interface events into changes to the model and defines the way the user-interface reacts to those events.
Implementation of MVC in a web site
Controller
Model
Browser Client
view1.jsp
view2.jsp
view3.jsp
Main.jsp
Views 1
2
3
4
5
Design of the EJB TierUML use cases: UML is the Unified
Modeling Language, the standard language for expressing the model of the software system that we intend to build.
Use cases are subset of UML that expresses the functionality of the software to be delivered. Use cases describe what to do, but not how to do it.
Analysis ObjectsInterface Objects : The interface object
is responsible for controlling access to the EJB tier from any client. An interface object should always be represented by a session bean in the implementation.
Ex : controller servlet for the web application’s model-view-controller architecture.
Control ObjectsControl objects provide services to
the application. They model functionality that is not naturally associated with a particular entity or interface. Control objects should be represented by session beans in the implementation.
Entity ObjectsEntity objects model those business
objects that should maintain their state after the use case completes. This means they represent data in the database. Entity beans are often represented by entity beans in the implementation model.
An Example of EJB DesignConsider the case of a company that develops
products, takes orders for those products, and then manufactures and ships them.
Actors in the company : An engineer, a web customer, a phone operator who takes orders from a catalog, floor manager who manages the manufacturing process, a crew member that actually builds the product ordered and a manager who tracks overdue orders.
Use CasesCreate a ProductPlace an OrderCancel an OrderSelect an Order for ManufactureBuild a ProductShip an OrderList Overdue Orders
Use case diagram from analysis
Engineer
Customer
Operator
Manager
Crew
M’ment
Create Product
Place Order
Cancel Order
Select Order
Build Product
Ship an Order
Overdue Orders
Stereotype icons in UMLInterface Object :
Entity Object :
Control Object :
Translation of analysis model into implementation
Actor User Interface Type Interface Object Impl’ation
Engineer Visual Basic Session Bean (RMI/IIOP) Customer Web Application JavaBean proxy / S Bean Operator Swing GUI Session Bean Manager Web Application JavaBean proxy / S Bean Crew Palm Pilot XHTML Servelet to Session Bean Management Web Application JavaBean proxy / S Bean
View of use case actors and their respective interface objects
Engineer
Customer
Operator
Manager
Crew
Manage--ment
VB App
Web App
Swing app
Web App
Web App
Palm App
View of interaction of interface and control objects
Shiporder
BuildProduct
Select
Cancel
Place
Create
ListOverdue
VBApp
WebApp
WebApp
Web App
SwingApp
PalmApp
View of interaction between control objects and entity objects
RoutingProduct
Order
Shipment
Account
SupplierShippingCompany
Customer
CreateProduct
PlaceOrderCancelOrder
Select forManufactureBuildProductShip OrderListOverdue
SummaryEJBs are intended for transactional systemsEJBs are portable, reusable server-side
components that execute in a containerAssist developer productivity, extend application
capability, and improve system stabilityAre accessible from many different types of
clientsThere are three types of beans : stateful session,
stateless session, and entity
SummaryThere are four major parts to every bean: the
home interface, the remote interface, the implementation class, and the XML deployment descriptor
The enterprise bean developer must follow certain rules to get the benefits of EJB technology
The roles of EJBs can be understood by analyzing a model of your enterprise in terms of interface, control and entity objects