OSGi bootcamp - part 2
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The document outlines the agenda for an OSGi bootcamp, focusing on design patterns, service dependency management, and practical examples of OSGi service implementation. Key topics include various design patterns such as Null-Object, Whiteboard, Singleton, Aspect, and Adapter services, along with dependency management strategies like Blueprint and Declarative Services. Additionally, it discusses event handling with Event Admin and Configuration Admin for managing service settings dynamically.
![Event Admin - Example
class MySubscriber extends DependencyActivatorBase implements EventHandler {
static final String[] topics ={ "com/acme/*",
"org/osgi/service/log/LogEntry/*" };
public void init(BundleContext context, DependencyManager dm) {
Dictionary dict = new Hashtable();
dict.put(EventConstants.EVENT_TOPIC, topics);
dict.put(EventConstants.EVENT_FILTER, "(bundle.symbolicName=com.acme.*)");
dm.add(createComponent()
.setInterface(EventHandler.class.getName(), dict)
.setImplementation(SampleComparator.class);
}
@Override
public void handleEvent(Event event) {
//...
}
}](https://image.slidesharecdn.com/osgibootcamp-2-151020132640-lva1-app6892/85/OSGi-bootcamp-part-2-35-320.jpg)
OSGi bootcamp - part 2
- 1. OSGi Bootcamp Day 2 Jan Willem Janssen
- 2. Agenda • OSGi design patterns • Managing service dependencies • more convenient options for easily managing service dependencies • The compendium • some sample services, sending and receiving events with EventAdmin and using and implementing the Log Service
- 3. Design Patterns for OSGi • Null-object pattern • Whiteboard pattern • Singleton services • Aspect services • Adapter services • Resource adapter services
- 4. Null Object Pattern An object that implements a certain interface, can be safely invoked and does nothing http://en.wikipedia.org/wiki/Null_Object_pattern
- 5. Whiteboard Pattern “don’t call us... we’ll call you” http://www.osgi.org/wiki/uploads/Links/whiteboard.pdf
- 6. Singleton Services • Binds logic in a single instance get() getVersions() get(version) store(Document) Document Repository Singleton Storage requires
- 7. Singleton Services manager.add(createComponent() .setInterface(DocumentRepository.class.getName(), null) .setImplementation(DocumentRepositoryImpl.class) .add(createServiceDependency() .setService(Storage.class)) ); manager.add(createComponent() .setInterface(Storage.class.getName(), null) .setImplementation(FileBasedStorage.class) );
- 8. Singleton Services • What if I don’t want singletons? • org.osgi.framework.ServiceFactory • org.osgi.framework.PrototypeServiceFactory • the consumer of the service is oblivious to this!
- 9. • Transparently inject an interceptor service • "in front of" all services matching a filter Aspect Services get() getVersions() get(version) store(Document) Repository Cache Aspect get() getVersions() get(version) store(Document) Repository intercepts
- 10. Aspect Services manager.add( createAspectService(DocumentRepository.class, null /* filter */, 10 /* ranking */, null /* autoConfig */ ).setImplementation(DocumentRepositoryCache.class) );
- 11. Adapter Services • Start an instance of the adapter service for any • "adaptee" service matching a filter getCacheHits() setSize() setTTL() flush() Repository Cache Manageable Adapter get() getVersions() get(version) store(Document) Repository Cache adapts
- 12. Adapter Services manager.add( createAdapterService(MyService.class, null), .setInterface(MyAdapterInterface.class.getName(), null /* filter */), .setImplementation(AdapterImpl.class)) );
- 13. Resource Adapters • Start an instance of a Resource Driven Service for all resources matching a filter • resources: any valid URL play() pause() stop() Audio Track Resource Adapter MP3 File adapts
- 14. Resource Adapters manager.add( createResourceAdapterService( "(path=*.mp3)" /* filter */, false /* propagate */, null /* callbackInstance */, “changed" /* callbackMethod */) .setInterface(AudioTrack.class, null) .setImplementation(MP3AudioTrack.class)) );
- 15. Dependency Management • Components need other services before: • they can publish their own service • they can do their work • Complex dependency graphs • hard to manage by hand • lots of boilerplate code
- 17. Dependency Libraries • Blueprint Services • spring inspired • XML • Declarative Services • OSGi standard • annotation/XML based
- 18. Dependency Libraries • iPOJO • similar to DS • extends OSGi service lifecycle • Dependency Manager • annotation/API-based • runtime control
- 19. Dependency Manager • API based dependency management • optional and required dependencies • supports extensible types of dependencies: • service dependency • configuration dependency • change dependencies dynamically at runtime
- 20. Dependency Manager • Extend DependencyActivatorBase, override init() and destroy() • Talk to the DependencyManager to: • create a new service object and: • set any service interface and properties; • set the implementation class; • add any service or configuration dependencies and: • make it required or optional • refer to a specific service or configuration
- 21. public class SampleComparator implements Comparator { private volatile LogService m_log; public int compare(Object o1, Object o2) { return o1.equals(o2) ? 0 : -1; } void start() { m_log.log(LogService.LOG_INFO, "Hello there!"); } } Dependency Manager - Example
- 22. public class Activator extends DependencyActivatorBase { public void init(BundleContext context, DependencyManager dm) { dm.add( createComponent() .setInterface(Comparator.class.getName(), null) .setImplementation(SampleComparator.class) .add(createServiceDependency() .setService(LogService.class) .setRequired(false))); } } Dependency Manager - Example
- 23. @Component public class SampleComparator implements Comparator { @ServiceDependency private volatile LogService m_log; public int compare(Object o1, Object o2) { return o1.equals(o2) ? 0 : -1; } @Start void start() { m_log.log(LogService.LOG_INFO, "Hello there!"); } } Dependency Manager - Example
- 24. • Add the DM annotation processor to bnd: -plugin: ${ext.repositories.-plugin}, org.apache.felix.dm.annotation.plugin.bnd.AnnotationPlugin; path:=${plugin-dir}/org.apache.felix.dependencymanager.annotation.jar Dependency Manager - Example
- 25. Dependency Manager • Create one or more components: manager.add(createComponent() ... • Use POJOs to implement services: .setImplementation(MyPOJO.class) • Optionally define the service interfaces: .setInterface(MySvc.class.getName, props) • Add dependencies
- 26. Service Dependencies • Are defined using the DependencyManager: .add(createServiceDependency() ... • Can be optional or required: .setRequired(boolean) • Track a specific service: .setService(LogService.class, “(name=mine)”) • Can be injected into an instance: .setAutoConfig(true) // this is the default • Can trigger callbacks on the instance: .setCallbacks(“addService”, “removeService”) // NOTE: callbacks can define any of the following parameters: (ServiceReference reference, Object service)
- 27. Dependency Life Cycle start Installed start Resolved Ac/veUninstalled end install stop uninstall Ac/ve Wai/ng6for6 required Monitoring6 op/onal ac/vatedeac/vate
- 28. Dependency Activation • If the reference to the implementation is a class, instantiate it, otherwise directly use the reference • Invoke the init() method on the instance • Inject all required and optional dependencies, using NullObjects where appropriate, and any BundleContext or ServiceRegistration • Invoke the start() method on the instance
- 29. OSGi compendium Log HTTP Device Access Configuration Admin Preferences Metatype Wire AdminUser Admin IO Connector Initial Provisioning UPnP™ Device Declarative Services Event Admin Service Tracker XML Parser Position Measurement and State Execution Environment Spec Remote Services Deployment Admin Blueprint Container
- 30. Log Service The Log Service Interface Log Service Specification Version 1.3 Figure 101.1 Log Service Class Diagram org.osgi.service.log package <<interface>> LogService <<interface>> LogReader Service <<interface>> LogEntry <<interface>> LogListener a Log Reader Service impl. LogEntry impl a Log user bundle a Log Service impl a Log reader user Log a message Store a message in the log for retrieval message log send new log entry retrieve log 1 1 1 0..n (impl dependent maximum) 1 0..n LogEntry has references to ServiceReference, Throwable and Bundle or register listener Bundle using Log Service Bundle using Log Reader Service Log implementation bundle
- 31. Log Service • an update of this spec is coming! • tries to solve many of the problems: • static logger • dynamic reconfiguration per logger • align API with SLF4J
- 32. Event Admin • Publish subscribe • Asynchronous and synchronous • Hierarchical topics • Decouple event creation and handling
- 34. Listen to Events • Create an EventHandler that listens to all events • Launch it in a framework that has an Event Admin implementation running
- 35. Event Admin - Example class MySubscriber extends DependencyActivatorBase implements EventHandler { static final String[] topics ={ "com/acme/*", "org/osgi/service/log/LogEntry/*" }; public void init(BundleContext context, DependencyManager dm) { Dictionary dict = new Hashtable(); dict.put(EventConstants.EVENT_TOPIC, topics); dict.put(EventConstants.EVENT_FILTER, "(bundle.symbolicName=com.acme.*)"); dm.add(createComponent() .setInterface(EventHandler.class.getName(), dict) .setImplementation(SampleComparator.class); } @Override public void handleEvent(Event event) { //... } }
- 36. Sending events • Add a service dependency to EventAdmin • Use either sendEvent() or postEvent() to send events
- 37. Event Admin - Example public class EventPublishingService { private volatile EventAdmin m_eventAdmin; private volatile LogService m_log; public void someLogic() { if (m_eventAdmin != null) { Dictionary properties = new Hashtable(); properties.put("timestamp", new Date()); m_eventAdmin.postEvent( new Event("com/acme/timer", properties)); } else { m_log.log(LogService.LOG_INFO, "unable to send event: no event admin!"); } } }
- 38. Configuration Admin • contains externally configurable settings for a service; • service is identified by its PID (persistent ID) • allows management systems to configure all settings; • settings can be created even before the actual bundle is installed. Bundle Component ManagedService service.pid6=6nl.luminis.store
- 39. Configuration Admin • Used for: • dynamically configuring singleton services (ManagedService) • creating new services based on configuration (ManagedServiceFactory)
- 41. Configuration Dependencies public class MyConfiguredService implements ManagedService { private volatile String m_name; @Override public void updated(Properties props) throws ConfigurationException { // check given properties if (props == null) { m_name = "<default>"; } else { // update local settings Object v = props.get("name"); if (v instanceof String) { m_name = (String) v; } else { throw new ConfigurationException("name", "must be a string!"); } } } // … }
- 42. Configuration Dependencies • Configuration updates are optional, but what about required configurations? • DependencyManager can help: • define a configuration dependency • our component is started only when the configuration becomes available • updated(props) is invoked before other life cycle methods of DM
- 43. Configuration Dependencies // Define in the init() of your activator: manager.add(createService() .setImplementation(MyConfiguredService.class) .add(createConfigurationDependency() .setPid("my.service.pid")) );
- 44. HTTP service • provides Servlet API • whiteboard style registration of: • listeners • filters • servlets
- 45. HTTP service Example public class MyServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { resp.setStatus(HttpServletResponse.SC_OK); resp.getWriter().print("Hello World"); resp.flushBuffer(); } }
- 46. HTTP service Example // Define in the init() of your activator: Properties props = new Properties(); props.put("osgi.http.whiteboard.servlet.pattern", "/hello"); manager.add(createService() .setInterface(Servlet.class.getName(), props) .setImplementation(MyServlet.class) );
- 47. OSGi tooling • The popularity of frameworks depend on their ease of use • OSGi development lacked in this area for long
- 48. OSGi tooling • Enter Bndtools: • actively developed plugin for Eclipse • makes it really easy to develop for/with OSGi: • automatic rebuilding of bundles • hot-deployment of bundles • very good support for semantic versioning
- 50. Books • Building Modular Cloud Apps with OSGi • Paul Bakker & Bert Ertman • Java Application Architecture Modularity Patterns with Examples using OSGi • Kirk Knoernschild
- 51. Links • https://github.com/jawi/osgi-tutorial contains the demo project as shown during the demo • http://bndtools.org/ the home of the Bndtools plugin for Eclipse • http://bnd.bndtools.org/ contains lots of information about the nitty-gritty details of Bnd • http://luminis.eu my current employer