OSGi and dynamic Java. An overview of dynamic modular applications using Swing and OSGi

Transcription

1 OSGi and dynamic Java An overview of dynamic modular applications using Swing and OSGi

2 Overview What is OSGi and what does it solve? OSGi bundles Lifecycle, installing, stopping and restarting Dynamic services Versioned bundle references

3 OSGi Open Standards Gateway initiative Formed to promote dynamic systems for embedded devices in 1999 Board composed of many different members Telecoms, software, automotive etc.

4 What does it do? Defines standard for modules a.k.a. Bundles OSGi provides open specification Several open-source engines Basis of several commercial tools

5 Problem Large are more complex than small systems Different parts evolve at different speeds Some parts need older versions than others E.g. only works with Xerces 2.4 but other parts need Xerces 2.6

6 Problem

7 Partial solution Build each part as separate Jar Maven does this; as do ant builds Define dependencies on those Jar names Use build tool that combines everything Doesn t solve the side-by-side problem

8 Improved solution Let each module declare its dependencies Dependencies can be versioned too Bind the modules together dynamically Can verify constraints met Allow modules to only see public API Can choose which packages to export

9 OSGi bundles Versioned, modular code

10 What is a bundle? Bundles are modular units Java code Resources Self-describing dependencies Just a JAR file with additional information!

11 What is a bundle? Manifest.MF Bundle-SymbolicName: org.example.helloworld Bundle-Name: HelloWorld example Bundle-Version: 1.0.0

12 Bundle Activator Runs code when a bundle is started/stopped Interacting with framework Examples Starting threads Listening to network sockets etc.

13 Bundle Activator HelloWorld.java package org.example; public class HelloWorld implements BundleActivator { public void start(bundlecontext c) { System.out.println( Hello World ); } public void stop(bundlecontext c) { System.out.println( Goodbye World ); } }

14 Bundle Activator Manifest.MF Bundle-SymbolicName: org.example.helloworld Bundle-Name: HelloWorld example Bundle-Version: Bundle-Activator: Import-Package: org.example.helloworld org.osgi.framework

15 A quick look at our first bundle...

16 Lifecycle

17 Bundle life cycle INSTALLED - framework has the bundle RESOLVED - all dependencies are met STARTING - getting ready to run ACTIVE - bundle is running STOPPING - shutting down

18 Installing a bundle Bundle installation can be done via URL Bundle.installBundle( OSGi tools provide ways of installing easily Equinox/Felix: install Knopflerfish: File -> Add bundle URL

19 Resolving and starting Resolution can happen automatically After installing/before starting Can also be done manually Start a bundle by numeric identifier Equinox/Felix: start 123 Knopflerfish: Bundle -> Start

20 Stopping and reinstalling Bundles can also be stopped Go back to RESOLVED state Can be updated Equinox/Felix: update 123 Knopflerfish: Bundle -> Update Can uninstall/install new bundles

21 A longer look at our second bundle...

22 Services

23 Bundle communication No bundle is an island Bundles can query for services Bundles can register services for others Data can be objects types Vector, String etc.

24 Service Registry Holds list of all services Mediates between bundles for services Informs listeners when services come/go ServiceTracker uses this information Can pass properties into a service E.g. username or other tokens

25 Services Services are registered by Java interfaces Find a service reference via bundle context Service reference returns the service Logically similar to HashMap of services Services can be registered with properties

26 Registering a service Bundle Activator start() method (usually) action = new ExampleAction(); properties = new Properties(); properties.put( tooltip, Using the action ); reference = context.registerservice( Action.class.getName(), action, properties);

27 Getting a service Bundle Activator start() method (usually) reference = context. getservicereference(action.class.getname()); // tooltip = reference.getproperty( tooltip ); action = (Action)context.getService(reference);

28 Dynamic services Services are dynamic and may come/go Service reference/service may be null/stale Should not cache references ServiceListener used to keep track ServiceTracker uses this for ease of use

29 ServiceTracker Bundle Activator start() method (usually) tracker = new ServiceTracker( context,action.class.getname(),null); tracker.open(); action = (Action)tracker.getService(); // tooltip = tracker.getservicereference() //.getproperty( tooltip );

30 Are you being served...

31 Dependencies

32 Dependencies A bundle can depend on other bundles Require-Bundle Import-Package Can export packages to dependents Export-Package

33 Exports and require HelloWorld Manifest.MF Bundle-SymbolicName: org.example.helloworld Export-Package: org.example Dependent Manifest.MF Bundle-SymbolicName: org.dependent Require-Bundle: org.example.helloworld

34 Exports and import HelloWorld Manifest.MF Bundle-SymbolicName: org.example.helloworld Export-Package: org.example Dependent Manifest.MF Bundle-SymbolicName: org.dependent Import-Package: org.example

35 Imports Only exported packages are visible E.g. org.example.internal.* invisible Imports/requires can be versioned Imports/requires acts as bundle classpath

36 Versions Versions are of the form major.minor.micro.qualifier major, minor and micro numeric zero if omitted qualifier is textual! <

37 Version ranges Ranges can be open or closed, or implicit [1.0.0,2.0.0) == <= version < (1.0.0,2.0.0] == < version <= x.y.z == [x.y.z, ) x.y == [x.y.0, ) x == [x.0.0, )

38 Versioned dependencies HelloWorld Manifest.MF Bundle-SymbolicName: org.example.helloworld Bundle-Version: Dependent Manifest.MF Bundle-SymbolicName: org.dependent Require-Bundle: org.example.helloworld; bundle-version=1.0.0

39 Multiple versions

40 Putting it all together...

41 The future of modular Java JSR 291 and JSR 277/294

42 OSGi/JSR291 OSGi now moving towards release 4.1 Been used for over 6 years (Java 1.2 days) Release 4 used for 1.5 years Proven solution for dynamic systems

43 OSGi-enabled software Open-source OSGi engines Knopflerfish Felix (neé Oscar) Equinox Libraries Spring OSGi

44 OSGi-enabled software Tools Lotus Notes Adobe Flex Application servers WebSphere 6.1 JOnAS 5

45 JSR277/294 Modular Java (Will) support modules as Jars (Will) have programmatic APIs only C.f. OSGi and declarative specifications Built-in to Java core by 2009? Makes a number of changes to Java spec

46 Comparison of JSR291 and JSR277/294 OSGi JSR277 Modules Yes Yes Any VM Yes >=1.7 SxS Yes No? Dynamic Yes No Updates Separate With VM Years use 6.5 0

47 Summary What is OSGi and what does it solve? OSGi bundles Lifecycle, installing, stopping and restarting Dynamic services Versioned bundle references

48 Questions

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