Software Architecture in Practice

1
Software Architecturein Practice

• RiSEs Seminars
• Basss et al. Book Chapter 16
• Fred Durão

2
Summary

• J2EE/EJB (Chapter 16)
• The J2EE Architectural Solution
• The EJB Architectural Solution
• EJB Programming
• Deployment Descriptors
• System Deployment Decisions

3
J2EE/EJB A case study of an Industry-Standard
Computing Infrastructure
4
History
J2EE/EJB Chapter 16

• In early 1990s was developed CORBA on which
• Distributed objects could communicate and
  interact with each other seamlessly and
  transparently.
• After, Sun Microsystems pushed the Java
  programming Language to support RMI (Remote
  Method Invocation)
• The Microsoft release the framework .Net
• In 1997 Sun Microsystems releases the framework
  J2EE/EJB

5
Requirements and qualities
J2EE/EJB Chapter 16

• The Wimbledon Tennis tournament experienced
  almost 1 billion Web access in 1999, with 420.000
  hits per minute (7000 per second) during one
  match
• J2EE/EJB aims to
• Provide a component-based architecture for
  building distributed OO applications in Java
• Scalability e.g. web access
• Availability 24/7
• Security - AA
• Usability access in different forms
• Performance latency
• Portability run in a variety of computing
  platforms
• Interoperability server side components
  implemented on different vendors
• Extensibility e.g. struts, JSF

6
Architectural Solution
J2EE/EJB Chapter 16

• 3 major features
• A multi-tiered distributed application model
• A server-side component model
• Built-in transaction control

• Components and Services
• EJB server-side component
• JSP
• Java Servelt
• JMS Java Message Service
• JNDI
• JTS Java Transaction Service
• JCA Java Connector Architecture
• COM Bridge
• RMI over IIOP
• JDBC

• Fontehttp//java.sun.com/j2ee/appmodel.html

7
The EJB Architectural Approach
J2EE/EJB Chapter 16
Fonte http//info.borland.com/techpubs/jbuilder/j
builder2005/enterprise/images/ejb-architecture.gif
8
The EJB Architectural Approach 2
J2EE/EJB Chapter 16

• Session Beans
• Stateless session beans
• Stateful session beans
• Entity Beans
• Container Manager Persistence
• Bean Manager Persistence

9
The EJB Architectural Approach achieving
qualities
J2EE/EJB Chapter 16
Goal Tactics Used
Availability/Reliability Heartbeat Transactions Passive Redundancy
Implementation Transparency Maintain existing interfaces Semantic Coherence
Interoperability Adherence to defined protocols
Performance Configuration Files Load balancing Maintain multiple copies
Scalability Load balancing
10
EJB - Programming
J2EE/EJB Chapter 16

• To create EJB server-side component, the
  developer must provide two interfaces
• Home
• Contain the life cycle methods of the EJB
• Remote
• Business methods offered by the bean

11
EJB Programming 2
J2EE/EJB Chapter 16
12
EJB Entity Bean
J2EE/EJB Chapter 16
13
EJB Interface Home
J2EE/EJB Chapter 16
14
EJB Remote Interface
J2EE/EJB Chapter 16
15
Deployment Descriptor
J2EE/EJB Chapter 16

• It is XML document associated with an EJB that
• Describes the type of the bean (session or
  entity)
• Describes the classes used for home, remote and
  the bean classes
• Specifies the transactional attributes (access
  control)
• Specified if the persistence in the entity bean
  is handled automatically by the container or
  performed explicitly by the bean code
• This the SEMANTIC COHERENCE tactic implemented

16
Deployment Descriptor ejb-jar.xml
J2EE/EJB Chapter 16
17
Database Descriptor
J2EE/EJB Chapter 16
18
State Management A performance decision
J2EE/EJB Chapter 16

• Stateful Session Bean
• Must be used to atomic actions
• else may high the overhead in terms of
  application performance
• Stateless Session Bean
• Many request to the server
• and persist the data on later
• E.g. shopping cart

19
Entity Bean to Use or Not Use? Thats the
question
J2EE/EJB Chapter 16

• Typical e-commerce system with an 85 read-only
  and 15 update transaction mix when implemented
  with entity beans achieved only half of this
  performance
• Causes of degradations
• Containersare the black boxes
• Bad state management
• Additional beans participate in the transaction

20
Distribution and Scaling Issues
J2EE/EJB Chapter 16

• Two ways of increasing the processing power in
  the server tier
• Scaling up, or vertical scaling
• Adding memory or faster processors in a single
  machine
• Scaling out, or horizontal scaling
• The server application is distributed across more
  the one machine
• Increased redundancy
• Cost efficiency

21
Distributed Transactions
J2EE/EJB Chapter 16

• Two phase commit protocol is often essential in
  building enterprise-wide system
• Is it always necessary?
• What about the overhead involved in managing
  them?
• What about several remote calls that pass over
  the network?
• What about the architect experience for that?

22
Resource Pooling Transactions
J2EE/EJB Chapter 16

• Connections to the databases do not need to be
  re-established continuously, thus improving
  application performance

23
Dependence on Java Virtual Machine Performance
J2EE/EJB Chapter 16

• If the heap size is big, garbage collection will
  be infrequentand this can slow down the server
  processing, giving the impression that the server
  is slow in unresponsive

24
References
J2EE/EJB Chapter 16

• Bass L., Clements P. and Kazman R. Software
  Architecture in Practice. Second Edition, 2003.
• a luz no fim do túnel pode ser um trem vindo em
  sua direção