OSGi DevCon 2013 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 scope of capabilities, standards coverage, tools support, and available implementations in an efforts to help OSGi users find a path to a component model best suited to their particular task.

1. © 2013 IBM Corporation
DS, BP, EJB, CDI, WTF!?
Graham Charters, IBM
OSGi DevCon US 2013
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2. © 2013 IBM Corporation
Agenda
 Background
 Criteria
 Component models
 How to choose
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Why?
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Approach
 Provide some criteria to consider when making a component model choice
 Explain a little bit about the technologies
 Describe how each rates against the criteria
 Reasons aren’t always technical
 We probably won’t always agree
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My beans are
dynamic and use
annotations.
Your beans smell!!

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Technical Criteria
 Extra-bean definition (e.g. XML-based
declarative model)
 Intra-bean definition (e.g. bean annotation-
based declarative model)
 Extensibility
 Enterprise Qualities of Service
 Quality of Integration with OSGi
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Non-technical criteria
 Open Standards
 Open Source implementations
 Choice of implementations
 Availability of tools
 Existing assets
 Existing skills
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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)
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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Declarative Services
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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)
Extensibility No
Enterprise QoS No
OSGi Integration Designed by OSGi for OSGi.
Includes Configuration
Admin
Open Standards OSGi Alliance
Implementations Eclipse Equinox &
Apache Felix
Tools BND & BNDTools
<component name=“DiscountCalculator“ …>
<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>
@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 ) { ... }
}

9. © 2013 IBM Corporation
Blueprint
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Criterion Blueprint
Inspiration Spring & Spring DM (standardized by
SpringSource)
Approach Extra-bean definition (XML-based
declarative model, includes bean-to-
bean 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
<?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>

10. © 2013 IBM Corporation
Enterprise JavaBeans
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Criterion EJB
Inspiration Version 1.0 - 15 years old this week!
Approach Inheritance & XML bindings (pre-3.0).
Intra-bean definition (bean annotation-
based 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 WebSphere Developer Tools (no
charge), Rational Application
Developer, Eclipse WTP
@Stateless
@Local(DiscountCalculator.class)
public class DiscountCalculatorImpl
implements DiscountCalculator {
@Resource(lookup="osgi:service/Logger")
private Logger logger;
public double discount() {
…
}
…
}

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Contexts and Dependency Injection
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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 None. Leverage CDI in other
component models (e.g. EJB)
OSGi Integration Core capabilities (Open Source)
Open Standards JCP, OSGi Alliance in progress
Implementations Weld-OSGi, Pax-CDI, Fighterfish
Tools EE Vendors tools
@Named
@RequestScoped
@OSGiComponent
public class DiscountCalculatorImpl
implements DiscountCalculator {
@Inject @OSGiService
StaticLogger logger;
public double dicount() {...}
...
}

12. © 2013 IBM Corporation
Some questions to ask when choosing
 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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No one component model to rule them all