Declarative Services Dependency Injection OSGi style

Declarative Services Dependency Injection OSGi style Felix Meschberger Day Management AG [email_address] Zurich, September 22 nd 2009

About Felix Meschberger
Senior Developer at Day Management AG
[email_address]
http://blog.meschberger.ch
OSGi Implementations @ Apache Felix
Declarative Services
Configuration Admin
Metatype Service

Contents
Dependency Injection
Implementations for OSGi
Issues
Maven SCR Plugin
Declarative Services 1.1

Loose Coupling
„ Don't call use, we'll call you“
Easier Testing
Inject different implementations
Popular in Spring Framework
Traditionally Descriptor Based
Current Trend: Java Annotations

Implementations for OSGi
iPOJO (Evolution of Declarative Services)
Spring DM
Blueprint Service (Evolution of Spring DM)
Peaberry (based on Google Guice)
… possibly more …

Version 1.0
Part of Compendium Services since R4
XML Descriptor Based
Lifecycle Management
Dependency Injection (Services)
Configuration Support

Component Descriptor
XML
Descriptors may be embedded
Namespace for Component
http://www.osgi.org/xmlns/scr/v1.0.0
Descriptors listed in Bundle Manifest Header
Service-Component
Multiple Components per Document

<scr:component name=“sample.component“ xmlns:scr=“...“> <implementation class=“org.sample.component“ /> <reference interface=“org.osgi.service.log.LogService“ bind=“bindLog unbind=“unbindLoad“ /> <property name=“p1“ value=“sample“ /> <property name=“p2“ type=“Integer“> 1 2 </property> </component>

Lifecycle Management
Load Descriptors on Bundle Start
Instantiation
Configuration
Activation
Deactivation
Unload on Bundle Stop

<scr:component name=“sample.component“ xmlns:scr=“...“> <implementation class=“org.sample.component“ /> <reference interface=“org.osgi.service.log.LogService“ bind=“bindLog unbind=“unbindLoad“ /> <property name=“p1“ value=“sample“ /> <property name=“p2“ type=“Integer“> 1 2 </property> </component>

Lifecycle Sample: Activation
package org.sample; public class Component { protected void activate ( ComponentContext c) { System.out.println(„Activating“); } protected void deactivate ( ComponentContext c) { System.out.println(„Deactivating“); } }

Lifecycle Sample: Binding
package org.sample; public class Component { protected void bindLog ( LogService ls) { this.logService = ls } protected void unbindLog ( LogService ls) { this.logService = null; } }

Lifecycle Sample: Configuration
package org.sample; public class Component { protected void activate ( ComponentContext c) { Dictionary props = c .getProperties() ; String p1 = (String) props.get(„p1“); int[] p2 = (int[]) props.get(„p2“); } }

Component Types
Regular Component (non-service)
Service
Service Factory
Component Factory

Event-based using bind/unbind methods
Lookup oriented using ComponentContext
Optionality
Multiplicity
Binding Policy

Configuration
Configuration from Configuration Admin
Properties from Descriptor
Provided through ComponentContext.getProperties()

Instantiation (non Factory)
If Enabled and Satisfied
Single Instance
No Configuration
Singleton Configuration ( service.pid )
Multiple Instances
Factory Configuration ( service.factoryPid )

Instantiation (Component Factory)
ComponentFactory.newInstance()
ComponentInstance.dispose()
Controlled by Application Only
Configuration may not be Factory Configuration

Descriptor Unvealed: Component
<scr:component name= enabled= immediate= factory= configuration-policy= activate= deactivate= > … Component Description …
</scr:component>

Descriptor Unvealed: Implementation
<implementation class= />

Descriptor Unvealed: Property
<property name= value= type= /> <property name= type= > … values … </property>

Descriptor Unvealed: Properties
<properties entry= />

Descriptor Unvealed: Service
<service servicefactory= > <provide interface= /> … More Provide Elements … </service>

Descriptor Unvealed: Reference
<reference name= interface= cardinality= policy= target= bind= unbind= />

Issue: Configuration Data Types
Wrapper of primitive types
Byte, Short, Integer, Long, etc.
String
Array or Vector
Primitive types
Wrappers of primitive types
String

Issue: XML Descriptor
Good to re-use legacy POJO
Problematic to keep in-sync with DS Classes
YAXF – Yet another XML File

Maven SCR Plugin
Generates Descriptors from Java Source
JavaDoc tags
@scr.component, @scr.property, ...
Java Annotations
@Component, @Property, ...
High Level Annotations
@SlingServlet

Issue: Not really POJO
Requires OSGi API for full functionality
Activate and Deactivate method names fixed
Configuration through ComponentContext
Service properties through ServiceReference
Fixed in Declarative Services 1.1

Declarative Services 1.1
Scheduled for OSGi R 4.2
Configurable names for (de)activator methods
More (de)activator method arguments
ComponentContext
BundleContext
Map
int/Integer (deactivator only)
Any combination

Declarative Services 1.1 (cont.)
More (un)bind method arguments
ServiceReference
Service instance
Service instance and Map
Configuration Dependency
Optional
Ignore
Require
Support for private properties

Declarative Services 1.1 (cont.)
Activator and bind methods may be
public (discouraged)
protected
private (if in the component class)
default (if in the same package)
Wildcards for Service-Component header

Questions

Thank You!

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Declarative Services Dependency Injection OSGi style

by Felix Meschberger on Jun 21, 2009

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Declarative Services Dependency Injection OSGi style — Presentation Transcript