OSGi Community Event 2013 (http://www.osgi.org/CommunityEvent2013/Schedule) ABSTRACT There are a number component models available to OSGi developers; Declarative Services (DS), Blueprint (BP), Enterprise JavaBeans (EJB), Contexts and Dependency Injection (CDI). Some have their roots in Java EE, some in open source projects such as the Spring Framework, others are standards at the OSGi Alliance, and some have DNA from all three. As is often the case where there are options available, there's rarely a one-size-fits-all. The 'right' choice may depend on the type of project you're working on, the existing assets, tools and skills at your disposal, and the runtime you're looking to deploy to. This talk will provide a brief overview of the four component models listed, describe their capabilities, standards coverage, tools support, and available implementations, and will show working examples of each, all in an effort to help OSGi users find a path to a component model best suited to their particular task. SPEAKER BIO Graham Charters is a Senior Technical Staff Member in the IBM WebSphere Application Server development organization. He is responsible for the OSGi Applications feature of the Application Server and a committer and PMC member of the Apache Aries OSGi programming model project. He is also the IBM technical lead in the OSGi Alliance Enterprise Expert Group.

1. OSGi DevCon US 2013
DS, BP, EJB, CDI, WTF!?
Graham Charters, IBM
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2. Agenda
 Background
 Criteria
 Component models
 How to choose
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3. Why?
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4. Approach
 Provide some criteria to consider when making a component model choice
 Explain a little bit about the technologies
My beans are
dynamic and use
annotations.
 Describe how each rates against the criteria
Your beans smell!!
 Reasons aren’t always technical
 We probably won’t always agree
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5. Technical Criteria
 Extra-bean definition (e.g. XML-based
declarative model)
 Intra-bean definition (e.g. bean annotationbased declarative model)
 Extensibility
 Enterprise Qualities of Service
 Quality of Integration with OSGi
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6. Non-technical criteria
 Open Standards
 Open Source implementations
 Choice of implementations
 Availability of tools
 Existing assets
 Existing skills
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7. The technologies: DS, BP, EJB, CDI, WTF
 Declaratives Services (DS)
 Blueprint (not commonly known as BP)
 Enterprise JavaBeans (EJB)
 Contexts and Dependency Injection (CDI)
 World Taekwondo Federation (WTF)
Now with
added demos!
There are a number of other component models, but I’ve focused on the ones I heard
discussed most often. They’re also all based on open standards
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8. The demo
Http Service
Whiteboard
Http Service
alias=/xyz
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Component
Servlet
Service
Time
Service
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9. Declarative Services
Criterion
DS
Inspiration
Popularity if DI frameworks, but
designed for OSGi
Approach
Extra-bean definition (XML-based
declarative model)
Build-time intra-bean definition
(annotations compiled to XML)
@Component
public class DiscountCalculatorImpl implements
DiscountCalculator {
private Logger logger;
@Reference(policy=DYNAMIC,
policyOption=GREEDY,
cardinality=MANDATORY)
void setLog( LogService log) { ... }
void unsetLog( LogService log) { ... }
void updatedLog( Map<String,?> ref ) { ... }
}
Extensibility
Schema extensibility
Enterprise QoS
No
OSGi Integration
Designed by OSGi for OSGi.
Includes Configuration
<component name=“DiscountCalculator“ …>
Admin
Open Standards
OSGi Alliance
Implementations
Eclipse Equinox &
Apache Felix
Tools
BND & BNDTools
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<implementation
class="com.acme.utils.impl.DiscountCalculatorImpl"/>
<service>
<provide
interface="com.acme.utils.DiscountCalculator"/>
</service>
<reference name=“log"
interface="org.osgi.service.log.LogService"
bind="setLog" unbind="unsetLog"
updated=“updateLog" />
</component>
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10. Blueprint
Criterion
Blueprint
Inspiration
Spring & Spring DM (standardized by
SpringSource)
Approach
Extra-bean definition (XML-based
declarative model, includes bean-tobean wiring)
Intra-bean definition (Annotations –
Apache Aries Open Source only)
Extensibility
Through XML namespaces
– no runtime standard
Enterprise QoS
Transactions and
Persistence (Apache
Aries), Security (WebSphere
Application Server), Bus
(CXF), Camel, etc…
OSGi Integration
Some life-cycle compromises
Config Admin (open source)
Open Standards
OSGi Alliance
Updates in pipeline
Implementations
Eclipse Gemini &
Apache Aries
Tools
WebSphere Developer Tools (no
charge), Rational Application Developer
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<?xml version="1.0" encoding="UTF-8"?>
<blueprint …>
<service id="DiscountCalculatorBeanService"
ref="DiscountCalculatorBean"
interface="com.acme.utils.DiscountCalculator" />
<bean id="DiscountCalculatorBean"
class="com.acme.utils.impl.DiscountCalculatorImpl">
<property name="logger" ref="loggerService" />
</bean>
<reference id="loggerService"
interface="com.acme.utils.Logger" />
</blueprint>
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11. Enterprise JavaBeans
Criterion
EJB
Inspiration
Version 1.0 - 15 years old
Approach
Inheritance & XML bindings (pre-3.0).
Intra-bean definition (bean annotationbased declarative model) (3.0 or later)
Extensibility
Nothing formal (defer to CDI)
Enterprise QoS
Transaction, Security, Remoting,
Persistence, Messaging
OSGi Integration
Core capabilities (proprietary)
Open Standards
JCP, OSGi specification in progress
Implementations
All JavaEE App Servers support EJB.
OSGi integration in WebSphere
Application Server, GlassFish, Apache
Aries, Apache OpenEJB
Tools
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@Stateless
@Local(DiscountCalculator.class)
public class DiscountCalculatorImpl
implements DiscountCalculator {
@Resource(lookup="osgi:service/Logger")
private Logger logger;
public double discount() {
…
}
…
}
WebSphere Developer Tools (no
charge), Rational Application
Developer, Eclipse WTP
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12. Contexts and Dependency Injection
Criterion
CDI
Inspiration
JBoss Seam, Google Guice & Spring
Approach
Intra-bean definition (annotation-based
life-cycle and DI model), Extra-bean
opt-in beans.xml with additional config
(e.g. extensibility)
Extensibility
Interceptors, Decorators & Portable
Extensions
Enterprise QoS
@Inject @Service
StaticLogger logger;
None. Leverage CDI in other
component models (e.g. EJB)
OSGi Integration
@Named
@RequestScoped
@Component
public class DiscountCalculatorImpl
implements DiscountCalculator {
Core capabilities (Open Source)
public double dicount() {...}
...
Open Standards
JCP, OSGi Alliance in progress
Implementations
Weld-OSGi, Pax-CDI, Fighterfish
Tools
EE Vendors tools
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13. Some questions to ask when choosing
No one component model to rule them all
 What existing skills does my team have?
– Choose the closest match (e.g. Spring? Consider Blueprint)
 What existing assets do I have available?
– Choose the closest match
 Do I need Enterprise capabilities?
– If “yes”, consider Blueprint or EJB, if “no”, consider DS
 Do I want something based on a standard?
– If “yes”, familarize yourself with the scope and direction of existing standards
 Do I need something based on open source?
– Apache Felix, Eclipse Equinox, Apache Karaf, Eclipse Gemini, Apache Aries, Eclipse
Virgo, ….the list goes on…..
 What are the capabilities of my target runtime?
– If a component model isn’t supported, there’s little point choosing it
 What are the capabilities of my tool chain?
– If a component model isn’t supported, you’re asking for pain
 What if I use more than one component model?
– Leverage OSGi services as the common integration point
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