Declarative Services Dependency Injection, OSGi Style
Felix Meschberger | Sr. Computer Scientist, Adobe Systems
Incorporated
About Felix Meschberger
Senior Computer Scientist
[email protected]
http://blog.meschberger.ch
OSGi Implementations @ Apache FelixDeclarative Services
Configuration Admin
Metatype Services
VP Apache Sling
OSGi Alliance Supporter
Contents
Dependency Injection
Implementations for OSGi
Declarative Services 1.0
Issues
Declarative Services 1.1
Maven SCR Plugin
Apache Felix Extensions
Dependency Injection
Loose CouplingDon't call us, we'll call you
Easier TestingInject different implementations
Popular in Spring Framework
Traditionally Descriptor Based
Current Trend: Java Annotations (JSR-330)
Implementations for OSGi
Apache Felix Dependency Manager
OSGi Declarative Services
Apache Felix iPOJO (Evolution of Declarative Services)
Spring DM
OSGi Blueprint (Evolution of Spring DM)
Peaberry (based on Google Guice)
probably more
Declarative Services
Version 1.0, Compendium R4
Version 1.1, Compendium R4.2
XML Descriptor Based
Lifecycle Management
Dependency Injection (Services)
Configuration Support
Lifecycle Management
Load Descriptors on Bundle Start
Instantiation
Configuration
Activation
Dependency Injection
Deactivation
Unload on Bundle Stop
Component Descriptor
XML
Descriptors may be embedded
Namespace for Componenthttp://www.osgi.org/xmlns/scr/v1.0.0
http://www.osgi.org/xmlns/scr/v1.1.0
Descriptors listed in Bundle Manifest
HeaderService-Component
Multiple Components per Document
Multiple Descriptors per Bundle
Component Descriptor
1
2
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);
}
}
Lifecycle: Binding
package org.sample;
public class Component {
protected void bindLog(LogService ls) {
this.logService = ls
}
protected void unbindLog(LogService ls) {
if (this.logService == ls) {
this.logService = null;
}
}
}
Lifecycle: Configuration
package org.sample;
public class Component {
protected void activate(ComponentContext c) {
Dictionary props = c.getProperties();
String p1 = toString(props.get(p1));
int[] p2 = toIntArray(props.get(p2));
}
}
Component Types
Regular Component (non-service)
Service
Service Factory
Component Factory
Dependency Injection
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
If Enabled and Satisfied
Single InstanceNo Configuration (unless required)
Singleton Configuration (service.pid)
Multiple InstancesFactory Configuration (service.factoryPid)
Component Factory
ComponentFactory.newInstance()
ComponentInstance.dispose()
Controlled by Application only
Global Singleton Configuration only
Descriptor Unvealed
Component Description
Descriptor Unvealed
Descriptor Unvealed
values
Descriptor Unvealed
More Provide Elements
Descriptor Unvealed
Issues
Configuration Data Types
Components not really POJO (DS 1.0)
XML Descriptor
Configuration Data
Wrapper of primitive typesByte, Short, Integer, Long, etc.
String
Array or VectorPrimitive types
Wrappers of primitive types
String
Aligned with...Metatype Service Specification
Configuration Admin Specification
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
DS 1.1
Configurable names for (de)activator methods
More (de)activator method argumentsComponentContext
BundleContext
Map
int/Integer (deactivator only)
Any combination
DS 1.1 (cont.)
More (un)bind method argumentsServiceReference
Service instance
Service instance and Map
Configuration DependencyOptional
Ignore
Require
Support for private properties
DS 1.1 (cont.)
Activator and bind methods may bepublic (discouraged)
protected
private (if in the component class)
default (if in the same package)
New features require DS 1.1 Namespace
Service-Component supports WildcardsE.g. OSGi-INF/ds*.xml
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 SourceJava
Annotations@Component, @Property, ...
High Level Annotations@SlingServlet
JavaDoc tags (deprecated)@scr.component, @scr.property, ...
Generates Metatype Service Descriptors
Alternative: Peter Kriens' BND library
Component Descriptor
1
2
SCR Annotations
package org.sample;
@Component
public class Component {
@Reference
private LogService log;
@Property(value = sample)
private String p1;
@Property(intValue = {1, 2})
private int[] p2;
protected void activate(
ComponentContext c) {
System.out.println(Activating);
}
protected void deactivate(
ComponentContext c) {
System.out.println(Deactivating);
}
}
Apache Felix Extensions
Management APISince Apache Felix SCR 1.0
Now also in Equinox DS 1.2.0v20100125
Service Reference: updatedSince Apache Felix SCR 1.4.0
OSGi Bug #63
Questions
Thank You!
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edit the title text formatClick to edit Master title style
22.03.11
2011 Adobe Systems Incorporated. All Rights Reserved.Click to
edit the title text formatClick to edit Master title style
22.03.11
2011 Adobe Systems Incorporated. All Rights Reserved.Click to
edit the title text formatClick to edit Master title style
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2011 Adobe Systems Incorporated. All Rights Reserved.
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Click to edit Master text styles
Second level
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3/22/11
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