Enterprise Applications

1
Enterprise Applications Java/J2EE Technologies
Dr. Douglas C. Schmidt d.schmidt_at_vanderbilt.ed
u http//www.dre.vanderbilt.edu/schmidt/
Professor of EECS Vanderbilt University
Nashville, Tennessee
2
Agenda

• What makes an application Enterprise?
• Java/J2EE to develop Enterprise Applications
• EJB Specification
• JBoss Application Server AOP
• What is an Architects role?

3
Enterprise Architectures

• They all have well thought out solutions to the
  -ilities of software development.

4
Enterprise -ilities

• Availability
• Dependability
• Distributability
• Maintainability
• Reusability
• Reliability
• Scalability
• Recoverability
• Etc

5
Availability

• The accessibility of a system resource in a
  timely manner for example, the measurement of a
  system's uptime.

6
Dependability

• ".. the trustworthiness of a computing system
  which allows reliance to be justifiably placed on
  the service it delivers .."
• IFIP WG10.4 on DEPENDABLE COMPUTING AND FAULT
  TOLERANCE

7
Distributability

• Involve Multiple Environments/Servers
• Can span across geographical locations
• Hand held devices to Multiprocessor Servers

8
Maintainability

• You are developing tomorrows legacy code
• To keep up or carry on continue.
• To keep in a condition of good repair or
  efficiency.
• What makes a system maintainable?

9
Reusability

• To use again, especially after salvaging or
  special treatment or processing.
• Reduces duplicate code / Copy Paste
• Easier to maintain
• Faster to develop

10
Reliability

• The trustworthiness to do what the system is
  expected or designed to do.
• Available 24-7-365
• Performs within acceptable thresholds

11
Scalability

• Refers to how much a system can be expanded. The
  term by itself implies a positive capability. For
  example, "the device is known for its
  scalability" means that it can be made to serve a
  larger number of users without breaking down or
  requiring major changes in procedure.
• Computer Desktop Encyclopedia

12
Recoverability

• Single point of failure
• Clustered servers
• Emergency backup plans
• Disaster backup plans

13
Questions / Comments?
14
Java/J2EE to develop Enterprise Applications

• EE Enterprise Edition
• Specifications and Standards
• Enabled Vendors to build Application Servers
• Focus on Business Logic, not on infrastructure
• Removed some complexities, introduced others

15
Standards Specifications
Some but not all

• EJB
• JSP
• JAXP
• JMS
• JNDI
• JMX

• Servlets
• JDBC
• JTA
• JCA
• RMI
• JNI

16
J2EE Architecture
17
Containers

• Containers provide the runtime support for J2EE
  application components. Containers provide a
  federated view of the underlying J2EE APIs to the
  application components. J2EE application
  components never interact directly with other
  J2EE application components. They use the
  protocols and methods of the container for
  interacting with each other and with platform
  services. Interposing a container between the
  application components and the J2EE services
  allows the container to transparently inject the
  services defined by the components deployment
  descriptors, such as declarative transaction
  management, security checks, resource pooling,
  and state management.
• -J2EE Specification v1.4

18
EJB Specification

• Session, Entity, and Message Driven Beans
• Instance Lifecycle
• Declarative Transaction Management
• Security
• Threading/Locking
• Remote/Local Invocation

19
Session Beans

• Executes on behalf of a single client.
• Can be transaction-aware.
• Updates shared data in an underlying database.
• Does not represent directly shared data in the
  database, although it may access and update such
  data.
• Is relatively short-lived.
• Is removed when the EJB container crashes. The
  client has to re-establish a new session object
  to continue computation.
• Can be either Stateful or Stateless.

20
When to use Session Beans

• Session Façade pattern
• Front end a web service
• Manage transactions, threading, pooling, etc.
• Expose a remote interface

21
Entity Beans

• Provides an object view of data in the database.
• Allows shared access from multiple users.
• Can be long-lived (lives as long as the data in
  the database).
• The entity, its primary key, and its remote
  reference survive the crash of the EJB container.

22
When to use Entity Beans

• Services that have a small limited object model.
• Object model needs to perform CrUD operations.
• No complex joins are needed to retrieve data.
• No need to walk complex object graphs.

23
Message Driven Beans

• Executes upon receipt of a single client message
  (JMS).
• Is asynchronously invoked.
• Can be transaction-aware.
• May update shared data in an underlying database.
• Does not represent directly shared data in the
  database, although it may access and update such
  data.
• Is relatively short-lived.
• Is stateless.
• Is removed when the EJB container crashes. The
  container has to re-establish a new
  message-driven object to continue computation.

24
When to use MDB

• Distributed systems
• JMS
• Asynchronous calls
• Manage Transactions, threading, pooling, etc.

25
Bean Lifecycle
26
Declarative Transactions

• Declare the transaction level through
  configuration of a bean.
• Container manages these transactions for you.
• Valid transaction Values

• Not Supported
• Required
• Supports

• Requires New
• Mandatory
• Never

27
Application Servers

• Implement the specification for EJB containers.
• Provide environment which allows developers to
  focus on business logic.

28
JBoss Application Server

• J2EE application server open source
• www.jboss.org
• EJB Container and more
• Implements Specification through Interceptors
  AOP-like

29
AOP Aspect Oriented Programming

• Aspect-Oriented Programming (AOP) complements
  OO programming by allowing the developer to
  dynamically modify the static OO model to create
  a system that can grow to meet new requirements.
  Just as objects in the real world can change
  their states during their lifecycles, an
  application can adopt new characteristics as it
  develops.
• -Graham ORegan

30
JBoss EJB Interceptor Stack
31
Implementing Declarative Transactions using
Interceptors

• Not Supported
• Required
• Supports
• Requires New
• Mandatory
• Never

32
Not Supported
33
Required
34
Supports
35
Requires New
36
Mandatory
37
Never
38
Custom Interceptors

• AOP Aspect Oriented Programming
• Logging
• Timing
• Metrics
• Any business logic that should be applied widely

39
Developers Focus on Business Logic