July 23 th, 2005 Software Architecture in Practice RiSE’s Seminars Bass’s et al. Book :: Chapter 16 Fred Durão

July 23th, 2005

Software Architecturein Practice

RiSE’s SeminarsBass’s et al. Book :: Chapter 16

Fred Durão

July 23th, 2005 2

Summary

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

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J2EE/EJB – A case study of an Industry-Standard Computing Infrastructure

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History

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

J2EE/EJB :: Chapter 16

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Requirements and qualities “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…


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Architectural Solution 3 major features

A multi-tiered distributed application model A server-side component model Built-in transaction control

Fonte:http://java.sun.com/j2ee/appmodel.html

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


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The EJB Architectural Approach

Fonte: http://info.borland.com/techpubs/jbuilder/jbuilder2005/enterprise/images/ejb-architecture.gif


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The EJB Architectural Approach {2}

Session Beans Stateless session beans Stateful session beans

Entity Beans Container Manager Persistence Bean Manager Persistence


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The EJB Architectural Approach – achieving qualities

Goal Tactics Used

Availability/Reliability HeartbeatTransactionsPassive Redundancy

Implementation Transparency Maintain existing interfacesSemantic Coherence

Interoperability Adherence to defined protocols

Performance Configuration FilesLoad balancingMaintain multiple copies

Scalability Load balancing


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EJB - Programming

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


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EJB – Programming {2}


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EJB – Entity Bean


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EJB – Interface Home


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EJB – Remote Interface


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Deployment Descriptor

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


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Deployment Descriptor – ejb-jar.xml


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Database Descriptor


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State Management – A performance decision

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


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Entity Bean – to Use or Not Use? That’s the question

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: Containers…are the black boxes Bad state management Additional beans participate in the transaction


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Distribution and Scaling Issues

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


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Distributed Transactions

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?


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Resource Pooling Transactions

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


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Dependence on Java Virtual Machine Performance

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


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References

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”


Documents

July 23 th, 2005 Software Architecture in Practice RiSE’s Seminars Bass’s et al. Book :: Chapter 16 Fred Durão