Declarative Services
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This document provides an overview of declarative services in OSGi, including: - Dependency injection using declarative services allows for loose coupling between components. - Implementations for OSGi include Declarative Services, iPOJO, Spring DM, and others. - Declarative Services uses XML component descriptors to define lifecycles, dependencies, and configurations. - Version 1.1 of Declarative Services introduced improvements like configurable lifecycle methods. - Issues with the XML format led to the creation of the Maven SCR plugin to generate descriptors from Java code.
![13
Lifecycle: 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“);
}
}](https://image.slidesharecdn.com/dsdevconlondon2010-101122092226-phpapp02/85/Declarative-Services-13-320.jpg)
![34
SCR Annotations
package org.sample;
@Component
public class Component {
@Reference
private LogService log;
@Property(value=“sample“)
private String p1;
@Property(value=“1,2“)
private int[] p2;
protected void activate(
ComponentContext c) {
System.out.println(„Activating“);
}
protected void deactivate(
ComponentContext c) {
System.out.println(„Deactivating“);
}
}](https://image.slidesharecdn.com/dsdevconlondon2010-101122092226-phpapp02/85/Declarative-Services-34-320.jpg)
![35
SCR JavaDoc Tags
package org.sample;
/** @scr.component */
public class Component {
/** @scr.reference /
private LogService log;
/** @scr.property value=“sample“ */
private String p1;
/** @scr.property values.0=“1“ values.1=“2“ */
private int[] p2;
protected void activate(
ComponentContext c) {
System.out.println(„Activating“);
}
protected void deactivate(
ComponentContext c) {
System.out.println(„Deactivating“);
}
}](https://image.slidesharecdn.com/dsdevconlondon2010-101122092226-phpapp02/85/Declarative-Services-35-320.jpg)
Declarative Services
- 1. Declarative Services Dependency Injection OSGi Style Felix Meschberger | Day Management AG
- 2. 2 About Felix Meschberger • Senior Developer at Day Management AG • fmeschbe@day.com • http://blog.meschberger.ch • OSGi Implementations @ Apache Felix – Declarative Services – Configuration Admin – Metatype Service
- 3. 3 Contents • Dependency Injection • Implementations for OSGi • Declarative Services • Issues • Declarative Services 1.1 • Maven SCR Plugin • Apache Felix Extensions
- 4. 4 Dependency Injection • 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
- 5. 5 Implementations for OSGi • Dependency Manager • Declarative Services • iPOJO (Evolution of Declarative Services) • Spring DM • Blueprint Service (Evolution of Spring DM) • Peaberry (based on Google Guice) • … possibly more …
- 6. 6 Declarative Services • Version 1.0, Compendium R4 • Version 1.1, Comendium R4.2 • XML Descriptor Based • Lifecycle Management • Dependency Injection (Services) • Configuration Support
- 7. 7 Component Descriptor • XML • Descriptors may be embedded • Namespace for Component – http://www.osgi.org/xmlns/scr/v1.0.0 – http://www.osgi.org/xmlns/scr/v1.1.0 • Descriptors listed in Bundle Manifest Header – Service-Component • Multiple Components per Document
- 8. 8 Component Descriptor <scr:component name=“sample.component“ xmlns:scr=“http://www.osgi.org/xmlns/scr/v1.1.0“> <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>
- 9. 9 Lifecycle Management • Load Descriptors on Bundle Start • Instantiation • Configuration • Activation • Dependency Injection • Deactivation • Unload on Bundle Stop
- 10. 10 Component Descriptor <scr:component name=“sample.component“ xmlns:scr=“http://www.osgi.org/xmlns/scr/v1.1.0“> <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>
- 11. 11 Lifecycle: 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“); } }
- 12. 12 Lifecycle: Binding package org.sample; public class Component { protected void bindLog( LogService ls) { this.logService = ls } protected void unbindLog( LogService ls) { this.logService = null; } }
- 13. 13 Lifecycle: 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“); } }
- 14. 14 Component Types • Regular Component (non-service) • Service • Service Factory • Component Factory
- 15. 15 Dependency Injection • Event-based using bind/unbind methods • Lookup oriented using ComponentContext • Optionality • Multiplicity • Binding Policy
- 16. 16 Configuration • Configuration from Configuration Admin • Properties from Descriptor • Provided through ComponentContext.getProperties()
- 17. 17 Instantiation • If Enabled and Satisfied • Single Instance – No Configuration (unless required) – Singleton Configuration (service.pid) • Multiple Instances – Factory Configuration (service.factoryPid)
- 18. 18 Component Factory • ComponentFactory.newInstance() • ComponentInstance.dispose() • Controlled by Application only • Global Singleton Configuration only
- 19. 19 Descriptor Unvealed <scr:component name= enabled= immediate= factory= configuration-policy= activate= deactivate= modified= > … Component Description … • </scr:component>
- 21. 21 Descriptor Unvealed <property name= value= type= /> <property name= type= > … values … </property>
- 23. 23 Descriptor Unvealed <service servicefactory= > <provide interface= /> … More Provide Elements … </service>
- 24. 24 Descriptor Unvealed <reference name= interface= cardinality= policy= target= bind= unbind= />
- 25. 25 Issues • Configuration Data Types • Components not really POJO (DS 1.0) • XML Descriptor
- 26. 26 Configuration Data • Wrapper of primitive types – Byte, Short, Integer, Long, etc. • String • Array or Vector – Primitive types – Wrappers of primitive types – String • Aligned with... – Metatype Service Specification – Configuration Admin Specification
- 27. 27 DS 1.0 not really POJO • Requires OSGi API for full functionality • Activate and Deactivate method names fixed and public or protected • Configuration through ComponentContext • Reference Service Properties through ServiceReference • Fixed in Declarative Services 1.1
- 28. 28 DS 1.1 • Configurable names for (de)activator methods • More (de)activator method arguments – ComponentContext – BundleContext – Map – int/Integer (deactivator only) – Any combination
- 29. 29 DS 1.1 (cont.) • More (un)bind method arguments – ServiceReference – Service instance – Service instance and Map • Configuration Dependency – Optional – Ignore – Require • Support for private properties
- 30. 30 DS 1.1 (cont.) • Activator and bind methods may be – public (discouraged) – protected – private (if in the component class) – default (if in the same package) • New features require DS 1.1 Namespace • Service-Component supports Wildcards – E.g. OSGi-INF/ds*.xml
- 31. 31 XML Descriptor • Good to re-use legacy POJO • Problematic to keep in-sync with DS Classes • YAXF – Yet another XML File
- 32. 32 Maven SCR Plugin • Generates Descriptors from Java Source – JavaDoc tags • @scr.component, @scr.property, ... – Java Annotations • @Component, @Property, ... – High Level Annotations • @SlingServlet • Alternative: Peter Kriens' BND library
- 33. 33 Component Descriptor <scr:component name=“sample.component“ xmlns:scr=“http://www.osgi.org/xmlns/scr/v1.1.0“> <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>
- 34. 34 SCR Annotations package org.sample; @Component public class Component { @Reference private LogService log; @Property(value=“sample“) private String p1; @Property(value=“1,2“) private int[] p2; protected void activate( ComponentContext c) { System.out.println(„Activating“); } protected void deactivate( ComponentContext c) { System.out.println(„Deactivating“); } }
- 35. 35 SCR JavaDoc Tags package org.sample; /** @scr.component */ public class Component { /** @scr.reference / private LogService log; /** @scr.property value=“sample“ */ private String p1; /** @scr.property values.0=“1“ values.1=“2“ */ private int[] p2; protected void activate( ComponentContext c) { System.out.println(„Activating“); } protected void deactivate( ComponentContext c) { System.out.println(„Deactivating“); } }
- 36. 36 Apache Felix Extensions • Management API – Since Apache Felix SCR 1.0 – Now also in Equinox DS 1.2.0v20100125 • Service Reference: updated – Since Apache Felix SCR 1.4.0 – OSGi Bug #63
- 37. 37 Questions
- 38. 38 Thank You!