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CS6320 – J2EE
L. Grewe
MOTIVATION: E-commerce and
Enterprise Computing Models
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Four models for e-commerce and
enterprise computing:
• Business to business
• Business to customer
• Customer to customer
• Intra-business
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Implementation technology has gone
through two-tier to componentbased n-tier architecture.
Why N-tier Systems Architecture
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Different presentations of the same business
data.
Change the business logic, or database type or
schema without impacting the clients.
Hide middle tier (business logic) behind a
firewall.
Database connection pools.
Selectively upgrade parts of the architecture
without rewriting the entire application.
N-tier Systems
Java™2 Platform, Enterprise
Edition (J2EE)
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J2EE is introduce to reduce the cost and
complexity of developing n-tired
enterprise applications
J2EE defines a complete platform that
guarantees services in such areas as:
•
•
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Security
Transaction Management
Resource Management
Naming and Directory
Messaging
Concurrency control
J2EE Architecture

The J2EE runtime environment
consists of four major parts:
• Application components
• Containers
• Resource manager drivers
• Database support
J2EE Application Components

J2EE defines four application
component types:
• Application clients
• Applets
• Servlets and JavaServer pages (JSP)
• Enterprise JavaBeans™ components
(EJB)
J2EE Containers
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J2EE supports four separate types of containers,
corresponding to the four types of components:
• Application client containers
• Applet containers
• Web containers
• Enterprise bean containers
All types of containers must provide Java 2
Platform Standard Edition (J2SE) compatible
runtime environment
J2EE Architecture
Benefits of J2EE Architecture
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J2EE server core manages resources and
transactions and includes the java 2 platform
virtual machine
J2EE platform services may be implemented on a
single system or distributed over disparate
platforms.
J2EE-compliant servers guarantee the seamless
and correct execution of all components and
middleware services.
Developers do not need to manage the
integration of service implementations from
various vendors (it is the J2EE platform vendor’s
responsibility).
Other benefits of J2EE Architecture
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Service API are specified as Enterprise Java
technology interfaces, which may be plugged
seamlessly into the server
The application server provides services such as:
• Load balancing
• Replication
• Database connection pooling
• Thread pooling
• Caching
J2EE is vendor independent – Application builders
can choose from a variety of server
implementations.
Component-based Server
Development
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The application server may be implemented using
reusable components.
Server components:
• Have well-defined business interfaces for their
clients.
• Interact with the container through welldefined API.
J2EE technology provides a set of vendorindependent programming interfaces for the
implementation of the container (middle tier).
Component-based Server
Development
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EJB technology forms one core of the
J2EE architecture.
Presentation logic is implemented
using servlets and JSP.
Business logic objects are
implemented as EJB and/or servlets.
Data layer represented with EJB.
J2EE Containers

J2EE containers provide:
• An environment and context for J2EE
components to execute.
• Resource management and other
system services to the components.
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Operating system processes.
Threads.
Container services are exposed to
components through interfaces (the
container itself is specified using
interfaces).
J2EE Connectors
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Connectors are used to integrate various
existing information systems in a J2EEbased application.
J2EE Connectors
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Leverage investments in existing
enterprise systems.
A connector is a vendor-specific
bridge used to link an existing
system to the J2EE system.
Connectors manage (and hide) all
the logic used to integrate with
proprietary systems and present
their services as JavaBeans
components.
J2EE Applications
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A J2EE application is a collection of
software components that are engineered
to be distributed across multiple tires of
an N-tier system. These software
components are implemented as EJB.
J2EE applications may play the role of a
client or a server depending on which tier
they are deployed.
J2EE applications are not required to be
distributed, but they should be engineered
so that they may be deployed on a
J2EE Application Components

There are two types of J2EE application
components: Web components for handling
presentation logic and EJB components for
handling the business logic.
• Web components are implemented as JSP or
servlets. These components shield the first-tier
clients from the complexity of the application
server.
• JSP presents application server services in a
form that is usable by any browser-based
client.
• Servlets manage the presentation of
application server services for clients such as
Java appplets, Java applications and Web
browsers.