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OSGi bootcamp - part 1

The document outlines the agenda and content from Day 1 of an OSGi Bootcamp led by Jan Willem Janssen, covering the introduction to OSGi, its core framework, and bundle creation. It discusses the history and evolution of OSGi, its current specifications, service-oriented architecture, and lifecycle management of bundles. Additionally, it includes technical aspects of service registration, event listening, and version management in OSGi.

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OSGi Bootcamp Day 1 Jan Willem Janssen
Agenda • Introduction to OSGi • The core framework • creating bundles, working with services, dealing with the dynamics and version resolution
OSGi history • Started as an embedded platform for the “home gateway” • Originally under the JCP as JSR-8 (1999) • OSGi alliance, consists of a large number of big companies, with the following mission: • Maintaining and publicising the OSGi specification • Certifying implementations • Organising events • Current version: OSGi Release 6
OSGi releases • R1: long ago :) • R2: October 2001 - JES, Oscar • R3: March 2003 - Knopflerfish • R4: August 2005 - Equinox • 4.1: May 2007 - small updates • 4.2: September 2009 - moving to the Enterprise • 4.3: April 2011 - generics & framework hooks • R5: June 2012 - generic resource/capability model • R6: June 2014 - framework updates • R7: 2016? - IoT ?
OSGi today OSGi technology is the dynamic module system for Java™ OSGi technology is Universal Middleware. OSGi technology provides a service-oriented, component- based environment for developers and offers standardized ways to manage the software lifecycle. These capabilities greatly increase the value of a wide range of computers and devices that use the Java™ platform.
OSGi Alliance • Expert Groups: • core platform (CPEG) • enterprise (EEG) • residential (REG) • IoT (IEG) • Working Groups: • marketing • requirements • technical steering committee
OSGi specification • Core • semantics • framework • core/mandatory services • Companion • optional services
Service Life%cycle Module OSGi Framework Java$Virtual$Machine Security Bundle Bundle Bundle OSGi%framework
OSGi Framework Layering Provides a publish/find/bind service model to for bundles to communicate in a decoupled way service module life-cycle Creates the concept of bundles that share classes in a controlled way according to constraints Manages the life cycle of bundles in a framework without requiring the VM be restarted
Module Layer (1/3) • A bundle is: • a JAR file • unit of deployment • own class loader • isolation • bundle classpath store Store.class Key.class store.fs StoreImpl.class FileSystem.class StreamU4l.class bundle store.fs.osgi Ac4vator.class META%INF/MANIFEST.MF Bundle%SymbolicName::store.fs Bundle%Version::1.0.2 Bundle%Classpath::.,:lib/fsuGl.jar Bundle%AcGvator: :store.fs.osgi.AcGvator
Module Layer (2/3) fs.nio3 Input.class Output.class store Store.class Key.class store.fs StoreImpl.class FileSystem.class StreamU4l.class bundle store.fs.osgi Ac4vator.class META%INF/MANIFEST.MF Bundle%SymbolicName::store.fs Bundle%Version::1.0.2 Bundle%Classpath::.,:lib/fsuGl.jar Bundle%AcGvator: :store.fs.osgi.AcGvator Export%Package::store:2.5.0 Import%package::fs.nio3:[1,:3)
Module Layer (3/3) ModuleBundle Bundle Bundle Bundle exports imports exports imports exports exports org.apache.u5l61.0 org.apache.u5l61.1org.apache.log62.3 org.apache.db61.4 • Consistency - ensures constraints are not violated • Class visibility - exporters may include/exclude specific classes • Bundle fragments - a single logical module in multiple physical bundles • Bundle dependencies - Allows for tight coupling when required
• Imagine bundle A somehow gets servlet instances from bundle B Importing & Exporting a Package (1/4) A B import javax.servlet export javax.servlet .class one3copy3of javax.servlet
• What if bundle A also wanted to get servlet instances somehow from bundle C? Importing & Exporting a Package (1/4) A B import javax.servlet export javax.servlet .class one3copy3of javax.servlet
• Bundle C could import from bundle B, but then it is dependent on it Importing & Exporting a Package (2/4) A B import javax.servlet export javax.servlet .class one3copy3of javax.servlet C import javax.servlet
• Bundle C could export its own servlet package, but bundle A could only see either C or B Importing & Exporting a Package (3/4) A C import javax.servlet export javax.servlet .class two3copies3of javax.servlet B export javax.servlet .class ???
Importing & Exporting a Package (4/4) • Bundle C could both import and export servlet to solve the dilemma A C import javax.servlet export1and1import javax.servlet .class B .class export1and1import javax.servlet
Advanced Consistency Checking • Sometimes more advanced consistency checking is necessary, consider this: Interface package org.foo.http; import javax.servlet; public interface HttpService { void registerServlet(Sting alias, Servlet servlet); } Metadata Export-Package: org.foo.http; version="1.0.0" Import-Package: javax.servlet; version="2.3.0"
Advanced Consistency Checking • Sometimes more advanced consistency checking is necessary, consider this: HTTP$ service A import javax.servlet version=2.3.0 export javax.servlet version=2.3.0 export org.foo.h=p
Advanced Consistency Checking • Sometimes more advanced consistency checking is necessary, consider this: HTTP$ service A import javax.servlet version=2.3.0 export javax.servlet version=2.3.0 export org.foo.h=p HTTP$ client import org.foo.h=p import javax.servlet version=2.4.0
Advanced Consistency Checking • Sometimes more advanced consistency checking is necessary, consider this: HTTP$ service A export javax.servlet version=2.3.0 export org.foo.h<p HTTP$ client B export javax.servlet version=2.4.0
Advanced Consistency Checking • Sometimes more advanced consistency checking is necessary, consider this: HTTP$ service A export javax.servlet version=2.3.0 export org.foo.h<p HTTP$ client B export javax.servlet version=2.4.0 This would result in a ClassCastException, why?
Advanced Consistency Checking • Sometimes more advanced consistency checking is necessary, consider this: HTTP$ service A export javax.servlet version=2.3.0 export org.foo.h<p HTTP$ client B export javax.servlet version=2.4.0
Advanced Consistency Checking • Sometimes more advanced consistency checking is necessary, consider this: HTTP$ service A export javax.servlet version=2.3.0 export org.foo.h<p HTTP$ client B export javax.servlet version=2.4.0 "uses" We need to declare such internal dependencies! Metadata Export-Package: org.foo.http; version=“1.0.0"; uses:="javax.servlet" Import-Package: javax.servlet; version="2.3.0"
Example Manifest Bundle-ManifestVersion: 2 
 Bundle-Name: Example Bundle
 Bundle-SymbolicName: net.luminis.example.bundle
 Bundle-Version: 1.0.0
 Import-Package: 
 org.osgi.framework;version=“1.3“, 
 org.osgi.service.event;version=“[1.1,2.0)“, 
 net.luminis.foo;resolution:=“optional“
 Export-Package: 
 org.osgi.service.event;uses:=org.osgi.framework;version=“1.1”
 
 X-MyBundleHeader:
 custom-attribute=“my-value”
Lifecycle Layer • Managed life cycle: - states for each bundle • Allows updating existing bundles - dynamically install, start, update, and uninstall Life%cycle start end install start stopuninstall installed star2ng stopping ac2veresolved uninstalled
Lifecycle Example Bundle OSGi+Framework provided package
Bundle OSGi+Framework Bundle Lifecycle Example install bundle
Lifecycle Example Bundle OSGi+Framework Bundle resolve bundle
Lifecycle Layer • The framework instantiates a class implementing BundleActivator • declared in the manifest • bootstraps your code by invoking start() • provides you a BundleContext for framework interaction
Lifecycle Layer public interface BundleContext {
 // …
 public Bundle[] getBundles();
 public Bundle installBundle(String location, InputStream input) 
 throws BundleException; public void addServiceListener(ServiceListener listener);
 public void addBundleListener(BundleListener listener);
 public void addFrameworkListener(FrameworkListener listener); public ServiceRegistration registerService(String clazz, 
 Object service, Dictionary properties); public ServiceReference[] getServiceReferences(String clazz, 
 String filter) throws InvalidSyntaxException; public Object getService(ServiceReference reference);
 // …
 }
Service Layer • OSGi framework 
 promotes service 
 oriented interaction 
 pattern among 
 bundles Service Log Store publish use use publish Prefs publish use Bundle Bundle Bundle Bundle Service' Provider Service' Requester Service' Registry publish interact find
Service Example Bundle OSGi+Framework provided package provided service
Service Example Bundle OSGi+Framework Bundle install bundle
Service Example Bundle OSGi+Framework Bundle resolve bundle
Service Example Bundle OSGi+Framework Bundle resolve service
Registering a service public class Activator implements BundleActivator {
 public void start(BundleContext context) throws Exception {
 Properties props = new Properties();
 props.put("author", "Jan Willem");
 
 context.registerService(
 MyService.class.getName(), new MyServiceImpl(), props);
 } public void stop(BundleContext context) throws Exception {
 // framework unregisters our services on our behalf…
 }
 }
Looking up and using a service 1. lookup a ServiceReference 2. get a reference to the service 3. invoke the method 4. (optional: unget the service)
Looking up and using a service ServiceReference reference = 
 context.getServiceReference(MyFirstService.class.getName());
 if (reference != null) {
 MyFirstService srv = 
 (MyFirstService) context.getService(reference);
 if (srv != null) {
 // use service
 // …
 context.ungetService(reference);
 } else {
 System.out.println("No service found");
 }
 } else {
 System.out.println("No service reference found!");
 }
Looking up using a query • You can both query on the service name and a filter condition • The filter condition allows you to query for properties • The filter syntax is similar to LDAP: • (key=value) or (&(name=john)(age>=18)) context.getServiceReferences(
 MyFirstService.class.getName(), 
 "(author=Jan Willem)");
Listening to the service registry • Using the bundle context, register as a ServiceListener • serviceChanged() will be invoked when a service is: • registered; • modified; • unregistering. public interface ServiceListener extends EventListener {
 public void serviceChanged(ServiceEvent event);
 }
Introducing the ServiceTracker • Makes the task of tracking services easier • You can just ask the ServiceTracker for a (list of) service(s) that match the conditions you specified • A ServiceTrackerCustomizer can be used to monitor changes or customise the service reference that is returned by the tracker • Found in org.osgi.util.tracker package
ServiceTracker example private ServiceTracker m_tracker; // initialise:
 m_tracker = new ServiceTracker(context, MyService.class.getName(), null);
 m_tracker.open(); 
 // usage:
 SomeService service = (SomeService) m_tracker.getService();
 if (service != null) {
 service.greet("John");
 }
 // cleanup:
 m_tracker.close();
Version Format • OSGi uses a 4-part version numbering scheme • <major>.<minor>.<micro>.<qualifier> • Major, minor, and micro are numeric values • Qualifier is a string value • Comparison (not always intuitive) • 1.0.0 < 1.9.9 < 1.10 • 1.0.0.beta > 1.0.0.alpha > 1.0.0
Version Format • Valid: • 1 • 1.10 • 1.9.9.alpha • 0.2.0.SNAPSHOT • Invalid: • 0.2.SNAPSHOT • 1.9.9-alpha
Version Range Format • Interval notation is used for version ranges • use '[' or ']' for inclusive values • use '(' or ')' for exclusive values
Version Range Format • Examples (quotes needed) • "[1.0.0,2.0.0)" == (1.0.0 <= v < 2.0.0) • "[1.1.2,1.2.3]" == (1.2.3 <= v <= 1.2.3) • "[1.1,2)" == (1.1.0 <= v < 2.0.0) • When a version range is expected, a single value represents an infinite range: • "1.0.0" == (1.0.0 <= v < ∞)
Semantic versioning • Major number change – signifies a backward incompatible update. • Minor number change – signifies a backward compatible update. • Micro number change – signifies an internal update (e.g., a bug fix or performance improvement). • Qualifier change – signifies a trivial internal change with “outward” noticeable difference, but nonetheless is a new artifact (e.g., line number refactoring).
Semantic versioning • OSGi whitepaper on semantic versioning • semver.org semantic versioning manifest
Downsides and Pitfalls <<"client">> Foo getBar() FooImpl <<"client">> Foo getBar() setBar() FooImpl uses implements update implements uses
Best Practice <<"client">> Foo FooImpl uses implements [1.0,/2.0) [1.0,/1.1)

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OSGi bootcamp - part 1

  • 1.
  • 2.
    Agenda • Introduction toOSGi • The core framework • creating bundles, working with services, dealing with the dynamics and version resolution
  • 3.
    OSGi history • Startedas an embedded platform for the “home gateway” • Originally under the JCP as JSR-8 (1999) • OSGi alliance, consists of a large number of big companies, with the following mission: • Maintaining and publicising the OSGi specification • Certifying implementations • Organising events • Current version: OSGi Release 6
  • 4.
    OSGi releases • R1:long ago :) • R2: October 2001 - JES, Oscar • R3: March 2003 - Knopflerfish • R4: August 2005 - Equinox • 4.1: May 2007 - small updates • 4.2: September 2009 - moving to the Enterprise • 4.3: April 2011 - generics & framework hooks • R5: June 2012 - generic resource/capability model • R6: June 2014 - framework updates • R7: 2016? - IoT ?
  • 5.
    OSGi today OSGi technologyis the dynamic module system for Java™ OSGi technology is Universal Middleware. OSGi technology provides a service-oriented, component- based environment for developers and offers standardized ways to manage the software lifecycle. These capabilities greatly increase the value of a wide range of computers and devices that use the Java™ platform.
  • 6.
    OSGi Alliance • ExpertGroups: • core platform (CPEG) • enterprise (EEG) • residential (REG) • IoT (IEG) • Working Groups: • marketing • requirements • technical steering committee
  • 7.
    OSGi specification • Core •semantics • framework • core/mandatory services • Companion • optional services
  • 8.
  • 9.
    OSGi Framework Layering Providesa publish/find/bind service model to for bundles to communicate in a decoupled way service module life-cycle Creates the concept of bundles that share classes in a controlled way according to constraints Manages the life cycle of bundles in a framework without requiring the VM be restarted
  • 10.
    Module Layer (1/3) •A bundle is: • a JAR file • unit of deployment • own class loader • isolation • bundle classpath store Store.class Key.class store.fs StoreImpl.class FileSystem.class StreamU4l.class bundle store.fs.osgi Ac4vator.class META%INF/MANIFEST.MF Bundle%SymbolicName::store.fs Bundle%Version::1.0.2 Bundle%Classpath::.,:lib/fsuGl.jar Bundle%AcGvator: :store.fs.osgi.AcGvator
  • 11.
  • 12.
    Module Layer (3/3) ModuleBundleBundle Bundle Bundle exports imports exports imports exports exports org.apache.u5l61.0 org.apache.u5l61.1org.apache.log62.3 org.apache.db61.4 • Consistency - ensures constraints are not violated • Class visibility - exporters may include/exclude specific classes • Bundle fragments - a single logical module in multiple physical bundles • Bundle dependencies - Allows for tight coupling when required
  • 13.
    • Imagine bundleA somehow gets servlet instances from bundle B Importing & Exporting a Package (1/4) A B import javax.servlet export javax.servlet .class one3copy3of javax.servlet
  • 14.
    • What ifbundle A also wanted to get servlet instances somehow from bundle C? Importing & Exporting a Package (1/4) A B import javax.servlet export javax.servlet .class one3copy3of javax.servlet
  • 15.
    • Bundle Ccould import from bundle B, but then it is dependent on it Importing & Exporting a Package (2/4) A B import javax.servlet export javax.servlet .class one3copy3of javax.servlet C import javax.servlet
  • 16.
    • Bundle Ccould export its own servlet package, but bundle A could only see either C or B Importing & Exporting a Package (3/4) A C import javax.servlet export javax.servlet .class two3copies3of javax.servlet B export javax.servlet .class ???
  • 17.
    Importing & Exportinga Package (4/4) • Bundle C could both import and export servlet to solve the dilemma A C import javax.servlet export1and1import javax.servlet .class B .class export1and1import javax.servlet
  • 18.
    Advanced Consistency Checking • Sometimesmore advanced consistency checking is necessary, consider this: Interface package org.foo.http; import javax.servlet; public interface HttpService { void registerServlet(Sting alias, Servlet servlet); } Metadata Export-Package: org.foo.http; version="1.0.0" Import-Package: javax.servlet; version="2.3.0"
  • 19.
    Advanced Consistency Checking • Sometimesmore advanced consistency checking is necessary, consider this: HTTP$ service A import javax.servlet version=2.3.0 export javax.servlet version=2.3.0 export org.foo.h=p
  • 20.
    Advanced Consistency Checking • Sometimesmore advanced consistency checking is necessary, consider this: HTTP$ service A import javax.servlet version=2.3.0 export javax.servlet version=2.3.0 export org.foo.h=p HTTP$ client import org.foo.h=p import javax.servlet version=2.4.0
  • 21.
    Advanced Consistency Checking • Sometimesmore advanced consistency checking is necessary, consider this: HTTP$ service A export javax.servlet version=2.3.0 export org.foo.h<p HTTP$ client B export javax.servlet version=2.4.0
  • 22.
    Advanced Consistency Checking • Sometimesmore advanced consistency checking is necessary, consider this: HTTP$ service A export javax.servlet version=2.3.0 export org.foo.h<p HTTP$ client B export javax.servlet version=2.4.0 This would result in a ClassCastException, why?
  • 23.
    Advanced Consistency Checking • Sometimesmore advanced consistency checking is necessary, consider this: HTTP$ service A export javax.servlet version=2.3.0 export org.foo.h<p HTTP$ client B export javax.servlet version=2.4.0
  • 24.
    Advanced Consistency Checking • Sometimesmore advanced consistency checking is necessary, consider this: HTTP$ service A export javax.servlet version=2.3.0 export org.foo.h<p HTTP$ client B export javax.servlet version=2.4.0 "uses" We need to declare such internal dependencies! Metadata Export-Package: org.foo.http; version=“1.0.0"; uses:="javax.servlet" Import-Package: javax.servlet; version="2.3.0"
  • 25.
    Example Manifest Bundle-ManifestVersion: 2
 Bundle-Name: Example Bundle
 Bundle-SymbolicName: net.luminis.example.bundle
 Bundle-Version: 1.0.0
 Import-Package: 
 org.osgi.framework;version=“1.3“, 
 org.osgi.service.event;version=“[1.1,2.0)“, 
 net.luminis.foo;resolution:=“optional“
 Export-Package: 
 org.osgi.service.event;uses:=org.osgi.framework;version=“1.1”
 
 X-MyBundleHeader:
 custom-attribute=“my-value”
  • 26.
    Lifecycle Layer • Managedlife cycle: - states for each bundle • Allows updating existing bundles - dynamically install, start, update, and uninstall Life%cycle start end install start stopuninstall installed star2ng stopping ac2veresolved uninstalled
  • 27.
  • 28.
  • 29.
  • 30.
    Lifecycle Layer • Theframework instantiates a class implementing BundleActivator • declared in the manifest • bootstraps your code by invoking start() • provides you a BundleContext for framework interaction
  • 31.
    Lifecycle Layer public interfaceBundleContext {
 // …
 public Bundle[] getBundles();
 public Bundle installBundle(String location, InputStream input) 
 throws BundleException; public void addServiceListener(ServiceListener listener);
 public void addBundleListener(BundleListener listener);
 public void addFrameworkListener(FrameworkListener listener); public ServiceRegistration registerService(String clazz, 
 Object service, Dictionary properties); public ServiceReference[] getServiceReferences(String clazz, 
 String filter) throws InvalidSyntaxException; public Object getService(ServiceReference reference);
 // …
 }
  • 32.
    Service Layer • OSGiframework 
 promotes service 
 oriented interaction 
 pattern among 
 bundles Service Log Store publish use use publish Prefs publish use Bundle Bundle Bundle Bundle Service' Provider Service' Requester Service' Registry publish interact find
  • 33.
  • 34.
  • 35.
  • 36.
  • 37.
    Registering a service publicclass Activator implements BundleActivator {
 public void start(BundleContext context) throws Exception {
 Properties props = new Properties();
 props.put("author", "Jan Willem");
 
 context.registerService(
 MyService.class.getName(), new MyServiceImpl(), props);
 } public void stop(BundleContext context) throws Exception {
 // framework unregisters our services on our behalf…
 }
 }
  • 38.
    Looking up andusing a service 1. lookup a ServiceReference 2. get a reference to the service 3. invoke the method 4. (optional: unget the service)
  • 39.
    Looking up andusing a service ServiceReference reference = 
 context.getServiceReference(MyFirstService.class.getName());
 if (reference != null) {
 MyFirstService srv = 
 (MyFirstService) context.getService(reference);
 if (srv != null) {
 // use service
 // …
 context.ungetService(reference);
 } else {
 System.out.println("No service found");
 }
 } else {
 System.out.println("No service reference found!");
 }
  • 40.
    Looking up usinga query • You can both query on the service name and a filter condition • The filter condition allows you to query for properties • The filter syntax is similar to LDAP: • (key=value) or (&(name=john)(age>=18)) context.getServiceReferences(
 MyFirstService.class.getName(), 
 "(author=Jan Willem)");
  • 41.
    Listening to theservice registry • Using the bundle context, register as a ServiceListener • serviceChanged() will be invoked when a service is: • registered; • modified; • unregistering. public interface ServiceListener extends EventListener {
 public void serviceChanged(ServiceEvent event);
 }
  • 42.
    Introducing the ServiceTracker •Makes the task of tracking services easier • You can just ask the ServiceTracker for a (list of) service(s) that match the conditions you specified • A ServiceTrackerCustomizer can be used to monitor changes or customise the service reference that is returned by the tracker • Found in org.osgi.util.tracker package
  • 43.
    ServiceTracker example private ServiceTrackerm_tracker; // initialise:
 m_tracker = new ServiceTracker(context, MyService.class.getName(), null);
 m_tracker.open(); 
 // usage:
 SomeService service = (SomeService) m_tracker.getService();
 if (service != null) {
 service.greet("John");
 }
 // cleanup:
 m_tracker.close();
  • 44.
    Version Format • OSGiuses a 4-part version numbering scheme • <major>.<minor>.<micro>.<qualifier> • Major, minor, and micro are numeric values • Qualifier is a string value • Comparison (not always intuitive) • 1.0.0 < 1.9.9 < 1.10 • 1.0.0.beta > 1.0.0.alpha > 1.0.0
  • 45.
    Version Format • Valid: •1 • 1.10 • 1.9.9.alpha • 0.2.0.SNAPSHOT • Invalid: • 0.2.SNAPSHOT • 1.9.9-alpha
  • 46.
    Version Range Format •Interval notation is used for version ranges • use '[' or ']' for inclusive values • use '(' or ')' for exclusive values
  • 47.
    Version Range Format •Examples (quotes needed) • "[1.0.0,2.0.0)" == (1.0.0 <= v < 2.0.0) • "[1.1.2,1.2.3]" == (1.2.3 <= v <= 1.2.3) • "[1.1,2)" == (1.1.0 <= v < 2.0.0) • When a version range is expected, a single value represents an infinite range: • "1.0.0" == (1.0.0 <= v < ∞)
  • 48.
    Semantic versioning • Majornumber change – signifies a backward incompatible update. • Minor number change – signifies a backward compatible update. • Micro number change – signifies an internal update (e.g., a bug fix or performance improvement). • Qualifier change – signifies a trivial internal change with “outward” noticeable difference, but nonetheless is a new artifact (e.g., line number refactoring).
  • 49.
    Semantic versioning • OSGiwhitepaper on semantic versioning • semver.org semantic versioning manifest
  • 50.
    Downsides and Pitfalls <<"client">>Foo getBar() FooImpl <<"client">> Foo getBar() setBar() FooImpl uses implements update implements uses
  • 51.