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Enterprise Java Beans
CS-422
Application Servers
• In the late 1980s and though the mid 1990s a number of corporations
(Broadvision, Netscape…) marketed a class of server products to
enable the creation of highly scaleable applications.
– Used proprietary interfaces to OLTP (On-line Transaction Processing)
tools like BEA Tuxedo and IBM TXSeries
• APIs are are not standardized
• Applications developed on one application server were not portable to
another application server
– every application ended up being custom written
• once one vendor‘s application server was installed, you were stuck with it and
at the mercy of that vendor
• vendor’s did a good job of convincing you how easy it was to use their product
but were really trying to sell customization and consulting services
WORA
• Java’s “Write Once, Run Anywhere” philosophy allows Java
applications to be written once and then run anywhere there is a JVM
• Java 2 Enterprise Edition (J2EE) allows WORA to be applied to
application server technology and server-side components to provide
an application server that will allow application portability
• Java 2 APIs are platform independent and vendor neutral
– each API provides a common programming interface to a generic type of
infrastructure service
– Java 2 APIs have the goal of extending Microsoft’s ODBC philosophy a
step further to include all infrastructure services
J2EE Industry Acceptance
• To be successful J2EE must have wide industry acceptance
– APIs would be useless if infrastructure vendors don’t implement support
for the J2EE APIs
– Sun made alliances with many Industry leaders to insure the success of
J2EE
• Transaction Management
– IBM, Compaq/Tandem, BEA Systems
• Persistence Management
– Oracle, Sybase, Informix
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Directory Services
– HP, Netscape, IBM
J2EE APIs
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Enterprise Java Bean (EJB) API
Java Naming and Directory Interface (JNDI)
Remote Method Invocation/Internet Inter-ORB Protocol
Java IDL
Servlets and JSP
Java Messaging Service (JMS)
Java Transaction Service JTS)
Java Transaction API (JTA)
Java Database Connectivity (JDBC)
EJB API
• The EJB API defines a server component model
– provides portability across application servers
– implements automatic services on behalf of the application components
JNDI API
• Provides access to naming and directory services
– DNS, NDS, NIS+, LDAP, COS
• used to look up interfaces used to create EJBs, JDBC connections and
other things
RMI/IIOP
• Allows the creation of remote interfaces for distributed computing
– default protocol (JRMP, Java Remote Method Protocol) is proprietary,
based on Java’s serialization APIs
– RMI-IIOP a JDK 1.3 extension of RMI that allows the use of IIOP
(Internet Inter ORB Protocol) for RMI communication. J2EE Spec
requires this as the standard protocol for communications between the
different tiers of the J2EE architecture.
Java IDL
• Creates remote interfaces to support CORBA communications in the
Java platform
– includes IDL compiler and a lightweight ORB
• allows the integration of non-Java based components
Servlets and JSP
• Used for creation of thin client interfaces for the presentation of
information and collection of user inputs
• Support the dynamic HTML generation and session management for
browser based clients
JMS
• Used for asynchronous communication between distributed objects
• Supports asynchronous communications through various messaging
systems, such as reliable queueing and publish-and-subscribe services
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JTA
• Provides a transaction demarcation API
• provides the infrastructure for transaction management
– open, committ, roll back
– if the transaction spans multiple beans deployed on the same server or on
widely dispersed servers, the server vendor is responsible for proper
implementation od transaction control
– transactions spanning multiple servers require the propigation of
transaction context between servers over IIOP
JTS API
• Defines a distributed transaction management service based on
CORBA’s Object Transaction Service
JDBC
• Provides uniform access to relational databases such as DB2, Oracle,
SQL Server and Sybase
• Provides provides interfaces to RDBMs both for data definition and
query/insert/update/delete
• latest version provides for database connection pooling
Where we stand on J2EE...
• In CS-328 we covered the following APIs:
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JDBC
RMI
JavaIDL
HTTP and the Web
JNDI
• In CS-422 we’ve covered:
– Servlets and JSP
• What’s left:
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JMS (to be covered in CS-328)
JTA (some day)
JTS (some day)
EJB
What is Enterprise Java Beans
• Defines a model for the development and deployment of reusable Java
server components
– Components are pre-developed pieces of applications code that can be
assembled into working application systems
• The EJB Architecture logically extends the Java Beans component
model to support server components
• Server components run in an application server
• A Java application server provides an optimized execution
environment for server-side Java application components
– by combining traditional OLTP (On-line Transaction Processing)
technologies with a Java application server delivers a high performance,
highly scalable, robust execution environment specifically suited to
support Internet enabled application systems
Containers
• J2EE doesn’t specify how a J2EE runtime should be built, but instead
provides an abstraction of the runtime infrastructure as a “container”
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Component contract
Container Service APIs
Declaritive services
Other container services
• The EJB Specification defines 4 types of containers:
– an applet container to run applets
– an application-client container for running standard Java application
clients
– a Web Container for hosting Java servlets and JSPs
– an EJB Container for hosting Enterprise Java Beans
J2EE Container Architecture
Applet Container
Applet
Web Container
EJB Container
Java Servlets
JSP Pages
EJBs
Application Client
Container
App.Client
J2EE Applicatiuon Server
Databases and
Other Resources
The EJB Container
• An EJB server must provide one or more EJB containers which
provide homes for the enterprise beans
• The EJB container manages the beans housed in it
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responsible of registering the bean
providing a remote interface for it
creating and destroying object instances
checking security
coordinate distributed trancactions
can optionally manage persistent data within the object
• any number of EJB claees can be installed in a particular conrainer but
each class can only be assigned to a particular container
EJB Container
The EJB Object interface intercepts all method calls
and implements transactions, state management,
persistence,and security services for the bean based
on deployment descriptor settings
Deployment
EJB Object
Descriptor
(Client view)
Client
Enterprise Bean
EJB Home
(bean identifier)
Environment
The EJB Home interface is accessible through JNDI
and implements all lifecycle services for the bean.
Transient and Persistent Objects
• Session Beans (transient object)
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session beans are created and exist usually for a single user session
performs operations on behalf of the client
may be transactional but are not usually recoverable after a system crash
can be stateless or can maintain conversational state across methods and
transactions
– container manages the conversational state of a session bean if it needs to
be evicted from memory
– must manage its own persistent data
• Entity Bean (persistent object)
– an object representation of persistent data that are maintained in a
permanent data store (like a database)
– a primary key identifies each instance of the entity bean
– are transactional and are recoverable following a system crash