Lecture 1: Introduction to JEE

Introduction to Java Platform,
Enterprise Edition (JEE)
Fahad R. Golra
ECE Paris Ecole d'Ingénieurs - FRANCE

Course Details
• Contents
• 10 sessions of 3 hours each
• 50% theoretical, 50% practical
!
• Assessment
• Assignment - 20%
• Course Project - 20%
• Surprise Quiz - 10%
• Final Exam - 50%
2 Introduction to Java Platform, Enterprise Edition

Course Contents
• JEE technology overview
• Servlets
• JSP, Expression Language
• Maven, JSTL
• Web Sockets
• Web Services
• EJB, JPA, Hibernate
• Java Servlet Faces

Lecture 1 - JEE Overview
• Multilayer architecture
• Transaction Processing
• 1-Tier, 2-Tier, 3-Tier & N-Tier architecture
• JEE Containers
• JEE architecture
• JEE APIs
• JEE Packaging

Multilayered software architecture
• A multilayered software architecture is a software
architecture that uses many layers for allocating the
different responsibilities of a software product.
!
• 'Layer' represents the orientation of the different
physical or conceptual elements that make up an
entire software solution
!
• 'Tier' represents the physical layout of the various
mechanisms in a system's infrastructure
5

3 Layers of Information System
presentation
layer
application logic
layer
resource management
layer
Client
informationsystem

Presentation Layer
• Controls how the
information system
presents information to
external entities and
accepts it from them.
!
• External entities are
users (UI) or other
information systems
(API)
presentation
layer
application logic
layer
resource management
layer
Client
informationsystem

Application Logic Layer
• The program
• Business process
• Business logic
• Business rules
presentation
layer
application logic
layer
resource management
layer
Client
informationsystem

Resource Management Layer
• Implements the
resource manager
!
• Takes care of ACID
properties
!
• We will discuss
them in coming
slides
presentation
layer
application logic
layer
resource management
layer
Client
informationsystem

Transaction Processing
• Business Transaction
• Interaction in real world
• Usually between enterprise & person or between enterprises
• Information processing that is divided into individual,
indivisible operations, called transactions
• Performs function on (shared) database
!
• Online Transaction Processing (OLTP)
• Runs a collection of transaction programs online

The ACID Properties
• A set of properties that guarantee that transactions
are processed reliably
• Atomicity
• Consistency
• Isolation
• Durability

Atomicity
• All (commit) or nothing (abort)
• "all or nothing": if one part of the transaction fails, the
entire transaction fails
• Example: transfer money between two bank accounts
!
• Must handle situations including power failures,
errors, and crashes

Consistency
• Each transaction takes valid states to valid states:
• Satisfy integrity constraints, triggers
!
• Sometimes the only notion of “valid” state is “a state
that could have been produced by executing a
sequence of transactions

Isolation
• Each transaction behaves as if it were executed in
isolation at some instant in time
!
• AKA Serializability
• Ensures that the concurrent execution of transactions
results in a system state that would be obtained if
transactions were executed serially
!
• Consistency + Isolation implies the data remains
consistent even when multiple transaction programs
execute concurrently

Durability
• The effect of a committed transaction will not be lost
• Even in the event of power loss, crashes, or errors
!
• So data must be on stable storage before commit
!
• Usually done with a log (or journal) that must be
forced before commit and used in case of crash
recovery

Resource Manager
• How ACID transactions are implemented
• Allocate resources to program executing a transaction
e.g. a locked record is a resource
!
• Reclaim resources in appropriate state on commit or
abort
!
• Handled at “Resource Management Layer”

Top down design
1. define access channels and
client platforms
2. define presentation formats
and protocols for the selected
clients and protocols
3. define the functionality
necessary to deliver the
contents and formats needed
at the presentation layer
4. define the data sources and
data organization needed to
implement the application
logic
presentation
layer
application logic
layer
resource management
layer
Client
informationsystem

Bottom up design
1. define access channels and
client platforms
2. examine existing resources
and the functionality they
offer
3. wrap existing resources and
integrate their functionality
into a consistent interface
4. adapt the output of the
application logic so that it
can be used with the
required access channels
and client protocols
presentation
layer
application logic
layer
resource management
layer
Client
informationsystem
Note: Used for Legacy Systems

1-Tier Architecture
• System is necessarily
monolithic
• May be highly efficient
!
• No stable service interface
API
• Problem of Legacy Systems
presentation
layer
application logic
layer
resource management
layer
Client
informationsystem

2-Tier Architecture
• Added flexibility in
presentation layer
• e.g. multiple specialised
presentation layers add
no complexity to
application
!
• Encouraged stable,
published APIs
• So clients could be
developed
presentation
layer
application logic
layer
resource management
layer
informationsystem
clientserver

2-Tier Architecture disadvantages
• A single server doesn’t scale

2-Tier Architecture disadvantages
• Integration of multiple services must be done at client

3-Tier Architecture
• Scalability at application
layer
• Multiple application
servers
!
• Application Integration
• Do it in the middle tier
!
• Encourage stable,
published APIs for
resource management
presentation
layer
application logic
layer
resource management
layer
informationsystem
clientservermiddleware

N-Tier architecture (Inductivity)
25 3-Tier 4-Tier 5-Tier

Enterprise application development
considerations
• Distributed computing protocols (RMI, CORBA, IIOP)
• Load balancing
• Persistence, back-end integration
• Transaction processing
• Clustering
• Runtime re-deployment, Server restarting
• Multi-threading
• Resource pooling
• Security, performance, optimization
• …..

Java Editions
• Java Platform Micro Edition:
• Mobile devices, set-top boxes etc
• Restricted form of Java
!
• Java Platform Standard Edition:
• Core libraries, what most people use in standard Java
programming
!
• Java Platform Enterprise Edition:
• Complete server-side enterprise-class development and
deployment platform

JEE
• Stands for “Java, Enterprise Edition”
!
• It is a collection of standards
• JDBC, JNDI, JMX, JMS
!
• It is a component technology
• Enterprise JavaBeans
!
• It is an “application server”
• Following in the footsteps of Component Transaction Monitors

JEE Containers
• JEE Infrastructure is divided into logical domains called
containers which host components.
• A container supports services related to security, transaction
management, Java Naming and Directory Interface (JNDI)
lookups, and remote connectivity
• The container also manages some of the connectors because it
is responsible for triggering events and instantiating
components
• The container also manages non-configurable services such as
enterprise bean and servlet life cycles, database connection
resource pooling, data persistence, and access to the Java EE
platform APIs

Java EE Server
• The runtime portion of a Java EE product. A Java EE server
provides EJB and web containers.

Enterprise JavaBeans (EJB) Container
• Manages the execution of enterprise beans for Java EE
applications. Enterprise beans and their container run on the
Java EE server.

Web Container
• Manages the execution of JSP page and servlet components for
Java EE applications. Web components and their container run
on the Java EE server.

Application Client Container
• Manages the execution of application client components.
Application clients and their container run on the client.

Applet Container
• Manages the execution of applets. Consists of a web browser
and Java Plug-in running on the client together.

JEE Architecture
• JEE specifications are interested in the activities:
• Development
• Deployment
• Execution
!
• Components to develop the code of the different elements of an application
• Web components
• Business logic components
• Containers to host the different components of an application
• Web container
• Application client container
• The supporting services for cross functional aspects
• Security, transactions, ...
• Communications infrastructure

JEE APIs
• An application programming interface (API) specifies
a software component in terms of its operations, their
inputs and outputs and underlying types.
!
• Its main purpose is to define a set of functionalities
that are independent of their respective
implementation

JEE APIs
• JEE APIs can be divided into two broad categories:
!
• Components
• Business logic components
• Presentation logic components
!
• Services
• Infrastructure services
• Communication services

JEE APIs - Components
• Business logic components:
• Enterprise JavaBeans
!
• Presentation logic components
• Servlets
• JSP
!
• These components are:
• Configured via Deployment Descriptors
• Deployed into containers

JEE APIs - Infrastructure Services
• JDBC (Java DataBase Connectivity) is an API for accessing
relational databases.
• JNDI (Java Naming and Directory Interface) is an API to access
naming services and business directories such as DNS, NIS,
LDAP, etc.
• JTA / JTS (Java Transaction API / Java Transaction Services) is
an API that defines standard interfaces with a transaction
manager.
• JCA (Java EE Connector Architecture) is an API to connect to the
enterprise information system (and Legacy systems)
• JMX (Java Management Extension) provides tools for managing
and monitoring applications, system objects, devices (e.g.
printers) and service oriented networks.

JEE APIs - Communication Services
• JAAS (Java Authentication and Authorization Service)
is an API for the managing authentication and access
rights.
• JavaMail is an API for sending email.
• JMS (Java Message Service) provides asynchronous
communication capabilities (called MOM Middleware
Message Object) between applications.
• RMI-IIOP (Remote Method Invocation over Internet
Inter-ORB Protocol) is an API that allows synchronous
communication between objects.

JEE Packaging
• Client application
• jar archive
• Web
• Gathers servlets and JSP and the resources required to
execute them (classes, tag libraries, images, ...)
• war archive + web.xml (optional in some cases)
• EJB
• Gathers EJBs and their components (classes)
• jar archive + ejb-jar.xml
• Enterprise Application
• ear archive (includes several jar and war modules) +
application.xml

Types of clients
• Fat client (Thick client) means a graphical client application
running on the operating system of the user. A thick client
generally has advanced processing capabilities and can
have a sophisticated graphical interface.
• Thin client refers to an application accessible via a web
interface (HTML) can be viewed using a web browser,
where all the business logic is processed on the server
side.
• Rich client (smart client) provide a graphical interface,
described with a grammar description based on XML
syntax, that allows a user's local applications to interact
with server-based applications through the use of Web
services.

Application Servers
• An application server is a server-side application
execution environment
!
• It supports all the features that allow multiple clients
to use the same application
!
• Application servers can provide:
• Only a web container (eg Tomcat)
• Only an EJB container (eg JBoss, Jonas, ...)
• Both these containers (eg Websphere, Weblogic, …)

Lecture 1: Introduction to JEE

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