7/28/2019 SCEA Study Sheet 1

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SCEA Study She

Compiled by Brian Briggman, Patricia Guimaraes, Konrad Ro

DOES NOT EXIST

READY

1. create

2. setSessionContext

3. ejbCreate

1. remove

2. ejbRemove

DOES NOT EXIST

METHOD READY

1. setSessionContext

2. ejbCreate 1. ejbRemove

PASSIVE

ejbActivateejbPassivate

DOES NOT EXIST

setEntityContext unsetEntityCon

1. remove

2. ejbRem

1. create

2. ejbCreate

3. ejbPostCreate

ejbActivate

POOLED

READY

ejbPassivate

Stateless Session Bean

Stateful Session Bean

Entity Bean

SCEA Study She

Scalability - Vertical/Horizontal expansion of the system to support more users

Maintainability - Correct flaws in a component without affecting other components

Reliability - Ensure integrity and consistency of system and transactions

Availability - Services are available to users

Extensibility - Add functionality without affecting other components

Performance - Optimization of resources, speed of execution

Manageability - Ensure health of the system

Security - Ensure data is not disclosed or modified illicitly

Architectural Considerations

Common Architectures

1-tier - monolithic, standalone

pros: manageability

cons: scalability, maintainability,

extensibility

2-tier - client/server, fat client,

stored procedures

3-tier/n-tier - typical J2EE architecture

Client Tier (web clients, applets)

Web Tier (web servers, JSP's, servlets)

Business Tier (EJB's)

EIS Integration Tier (JDBC, ODBC, Corba)

EIS Tier (databases, legacy data)

EJB Container Model

Applicability of J2EE

Enterprise JavaBeans (EJB's)

Atomic - all or none of transaction is performedConsistent - obeys integrity constraintsIsolated - independent of other transactionsDurable - data must persist once transaction is over

Distributed system frameworksCORBA - moves state of object (call by value)RMI - moves state and behavior (call by referen

RMI-JRMP: Used for pure Java applicationsRMI-IIOP: Standard protocol for EJB's, calls COR

Java IDL: Used when calling Java with CORBAJNI: Java wrapper around native code

Stateless Session Beans (SLSB) -Used to provide generic servicesBusiness logic

Stateful Session Beans (SFSB) -Maintain conversational state (shopping carts)Business logic

Entity Beans (EB) -Model business entities (nouns)Usually represents a row in the databaseProvides concurrent access to shared dataShould be accessed via session beans

Data Access Objects (DAO)Place DB access logic in DAO's, not EJB'sResults in greater database portability

AttributeRequiredRequiresNewNotSupportedSupportsMandatoryNever

Client Has TransactionPropagatedSuspended & NewSuspendedPropagatedPropagatedException

No TransactNewNew--Exception-

The container provides:1) Life cycle management2) Transaction management3) Object distribution

Transactions

EJB Lifecycles

Each EJB must have:Home Interface (extends javax.ejb.EJBHome)- allows client to create/remove/find an EJB

Remote Interface (extends javax.ejb.EJBObject)- contains business methods callable by client

Bean class (extends javax.ejb.SessionBeanor javax.ejb.EntityBean)

- contains implementation of Home and Remoteinterface methods and lifecycle methods

Bean Passivation: container canserialize beans to disk to freeresources

ejbPassivate/ejbActivate can beimplemented to close/reopenexternal connections

For SFSB's, ejbPassivate must alsonull all non-transient, non-serializable fields

Bean Pooling: container managesbean instances in a pool to

conserve resources

pooling increases scalability

NameStateless SessionStateful SessionEntity

PassivationNoYesYes

CMTYesYesYes

BMTYesYesNo

CMP--

Yes

BMP--

Yes

Beans have the following properties:

Container vs Bean Managed TransactionsCMT: Declarative, less codeBMT: More control, only in Session Beans

EJB does not support nested transactions

Container vs Bean Managed PersistenceCMP: better portability across databases,

simple datatypes onlyBMP: can perform better,

complex datatypes

Legacy Connectivity

Screen scraper- acts as terminal emulator on one endand an object interface on the other

- used if no access to source codeObject mapping- wrappers map legacy objects tonewer interfaces

- used if legacy interface changes oftenOff-board serverserves as a proxy for legacy systemoften used with screen scrapers