OSGi Best Practices - Tim Ward

Legal> IBM and WebSphere are trademarks or registered trademarks of International Business Machines Corp., registered in many jurisdictions worldwide.> Java and all Java-based trademarks and logos are trademarks or registered trademarks of Oracle and/or its affiliates.> OSGi and the OSGi logo are trademarks or registered trademarks of the OSGi Alliance> Other product and service names might be trademarks of IBM or other companies. A current list of IBM trademarks is available on the Web at “Copyright and trademark information” at www.ibm.com/legal/copytrade.shtml 2 Page 2 OSGi Alliance Community Event 2011© 2008-2011. All Rights Reserved, 21.09.11 © IBM Corp. 2011

Modularization in Java Jar> Jars have no modularization Package characteristics – No “jar scoped” access modifiers. Class Class Class – No means for a jar to declare its Package dependencies. Class Class – No versioning. Class Package Class Class Class Page 4 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

Problems with Global Java ClassPath Java VM party common resolver axis xerces rt assetmaint catalina mail ezmorph xmlapisBegin jce hhfacility base jenks servlets xmlrpcHere jsse pos. datafile jakarta jetty xmlgraphics plugin content entity log4j looks sunjce_prov. manufact. widget httpunit jdbm dnsns product … mx4j bsf Class .. bi rome batik bsh Not marketing workflow jpos18 fop velocity Found Exception workeffort ecommerce jcl tomcat ws-commons ebay oagis barcode4j poi geronimo minerva … freemarker lucene .. minilang googlebase serializer jdom json accounting order naming commons xalan guiapp ofbiz jython derby wsdl4j Page 5 OSGi Alliance Community Event 2011© 2008-2011. All Rights Reserved, 21.09.11 © IBM Corp. 2011

webA.warProblems with EARs/WARs WEB-INF/classes/servletA.class WEB-INF/lib/spring.jar WEB-INF/lib/commons-logging.jar WEB-INF/lib/junit.jar…Enterprise Applications have isolated webB.war WEB-INF/classes/servletB.classclasspaths but… WEB-INF/lib/spring.jar WEB-INF/lib/commons-logging.jar WEB-INF/lib/junit.jar… webC.war WEB-INF/classes/servletC.class> No Sharing WEB-INF/lib/spring.jar – Common libraries/frameworks in apps WEB-INF/lib/commons-logging.jar WEB-INF/lib/junit.jar… and memory> Version conflicts plankton.v1 plankton.v2 Page 6 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

What is OSGi?“The dynamic module system for Java”> Mature 10-year old technology> Governed by OSGi Alliance: http://www.osgi.org> Used inside just about all Java-based middleware – IBM WebSphere, Oracle WebLogic, Red Hat JBoss, Sun GlassFish, Paremus Service Fabric, Eclipse Platform, Apache Geronimo, (non-exhaustive list) http://www.osgi.org/wiki/uploads/News/2008_09_16_worldwide_market.pdf Package Jar Package Jar Explicit exports Clas Clas Clas Clas Clas Clas ss Package ss Package s s Clas Clas Clas Clas Clas Clas ss ss s Explicit dependencies s Page 8 OSGi Alliance Community Event 2011© 2008-2011. All Rights Reserved, 21.09.11 © IBM Corp. 2011

OSGi Bundles and Class Loading OSGi Bundle – A jar containing: Classes and resources. Bundle Class Loading OSGi Bundle manifest. Each bundle has its own loader. What’s in the manifest: No flat or monolithic classpath. Bundle-Version: Multiple versions of bundles can live concurrently. Class sharing and visibility decided by declarative dependencies, not Import-Package: What packages by class loader hierarchies. from other bundles does this bundle depend upon? OSGi framework works out the dependencies including versions. Export-Package: What packages from this bundle are visible and reusable outside of the bundle?Manifest-Version: 1.0Bundle-ManifestVersion: 2Bundle-Name: MyService bundleBundle-SymbolicName: com.sample.myserviceBundle-Version: 1.0.0Bundle-Activator: com.sample.myservice.ActivatorImport-Package: com.something.i.need;version="1.1.2"Export-Package: com.myservice.api;version="1.0.0" Page 9 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

OSGi Service Registry• Service • An object associated with a list of classes (usually interfaces) it provides • Dynamic (can come and go), framed by bundle lifecycle • Services are the primary means of collaboration between bundles. S Page 11 OSGi Alliance Community Event 2011© 2008-2011. All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP1 - Use Import-Package not Require-Bundle Require-Bundle – Tightly coupled with a particular bundle with the specified symbolic name and version – High coupling between bundles MANIFEST.MF – Import all packages ... Require-Bundle: com.ibm.ws.service;bundle-version=2.0.0 – Bundle version management• Import-Package – Can wire to any bundles exporting the specified package – Loose coupling between bundles – Only import the package you need MANIFEST.MF ... – Package version management Import-Package: com.ibm.ws.service.api;version=2.0.0 Page 13 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP2 - Avoid split packages• Split package – A package is exported by two bundles at the same version and the set of classes provided by each bundle differs.• Why? – Leads to the use of Require-Bundle, compromising the extent to which systems using the bundles can be extended and maintained.• How? – Keep all of the classes from any one package in a single bundle Page 14 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP2 - Split Package examples API A Implementation C org.hal.api 1.0.0 org.hal.a 1.0.0 API B Bundle C has to use Require-Bundle to org.hal.api 1.0.0 ensure that it has classes from both parts of the API Figure 1. Consumers of split packages need to use the Require-Bundle headerPage 15 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP2 - Split Package examples API A Implementation C org.hal.a 1.0.0 org.hal.api 1.0.0 Figure 2. A complete package exported from a single bundle maintains high bundle cohesionPage 16 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP3 - Version bundles and packages• What is semantic versioning? – Uses a major.minor.micro.qualifier numbering scheme • Major - Packages with versions that have different major parts are not compatible both for providers as well as consumers. • Minor – API enhancement, e.g. adding methods to an API • Micro – bug fixing • Qualifier – identifier such as timestamp • Example: 1.1.2.20101122am, 1.0.0, 2.0 – Changes in major: a binary incompatible, minor: enhanced API, micro: no API changes• Why? – Clients can protect themselves against API changes that might break them. Page 17 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP3 - Version bundles and packagesexamples API A org.hal.a 1.0.0 Implementation A Client A Imports: Imports: org.hal.a [1.0, 1.1) org.hal.a [1.0, 2.0) API B org.hal.a 1.0.0 Figure 3: A client and an implementation can use either of two equivalently versioned packages Implementation A API A Client A Imports: Imports: org.hal.a [1.0, 1.1) org.hal.a 1.0.0 org.hal.a [1.0, 2.0) Implementation B API B Client B Imports: Imports: org.hal.a 1.1.0 org.hal.a [1.1, 1.2) org.hal.a [1.1, 2.0) Figure 4: How a client and implementation are affected differently by a minor API version change Page 18 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP3 - Version bundles andpackages examples Implementation A Client A Imports: org.hal.a 1.0.0 Imports: org.hal.a [1.0, 1.1) org.hal.a [1.0, 2.0) API A Implementation B API B Client B Imports: Imports: org.hal.a [2.0, 2.1) org.hal.a 2.0.0 org.hal.a [2.0, 3.0) Figure 5. How clients and implementations are similarly affected by a major API version change Page 19 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP4 - Separate API from Implementations• Why? – Great flexibility – Many implementation bundles → enable more services provided – Reduce package dependencies → reduce circular dependencies• How? – Put API classes in one bundle – Put implementation classes in a separate bundle Page 20 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP4 - Separate API andimplementation examples API + Implementation Client org.hal.myapi org.hal.b.client org.hal.a.impl Both API and implementation packages imported by clientFigure 6. Badly designed provider bundle where the API and implementation classes are in the same bundle Page 21 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP5 - Share services not implementations• Use the OSGi service registry to construct instances• Why? – Able to obtain an instance of an implementation without knowing which one – Achieve a loosely coupling of client, API and implementation• How? – Register an instance of the API interface in the OSGi service registry – Register an implementation of the OSGi ServiceFactory interface in the OSGi service registry. Page 22 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP4 & 5 - examples API Client org.hal.myapi org.hal.b.client Implementation org.hal.a.impl API and implementation packages in different bundles but still imported by client Figure 7. Badly designed provider bundles where the API and implementation classes have been separatedPage 23 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP4 & 5 - examples API Client org.hal.myapi org.hal.b.client Implementation org.hal.a.impl Client and implementation in separate bundles, both import API. Client uses implementation through a service defined by the API. Figure 8: Well designed provider bundles where the API and implementation classes have been separatedPage 24 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

Using services can be hard!private BundleContext ctx; @Override public void serviceChanged(ServiceEvent event)private AtomicReference<LogService> ls = new {AtomicReference<LogService>(); ServiceReference ref = event.getServiceReference();private AtomicReference<ServiceReference> lr = newAtomicReference<ServiceReference>(); if (ls.get() == null && event.getType() == ServiceEvent.REGISTERED) {public void start(BundleContext ctx) throws ls.set((LogService) ctx.getService(ref));InvalidSyntaxException{ } else if (ls.get() != null && event.getType() == ServiceEvent.UNREGISTERING &&this.ctx = ctx; ref == lr.get()) {ctx.addServiceListener(this, ref = ctx.getServiceReference(LogService.class.getName());"(objectClass=org.osgi.service.log.LogService)"); if (ref != null) {ServiceReference ref =ctx.getServiceReference(LogService.class.getName()); ls.set((LogService) ctx.getService(ref));if (ref != null) { lr.set(ref);ls.set((LogService) ctx.getService(ref)); }lr.set(ref); }} }} Page 25 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP6 - Use Blueprint dependencies injected publishes consumes service service OSGI-INF/blueprint/ A static assembly and blueprint.xml configuration of components (POJOs) Blueprint bundle• Specifies a Dependency Injection container, standardizing established Spring conventions• Configuration and dependencies declared in XML “module blueprint”, which is a standardization of Spring “application context” XML. – Extended for OSGi: publishes and consumes components as OSGi services• Simplifies unit test outside either Java EE or OSGi r/t.• The Blueprint DI container can be a part of the server runtime (compared to the Spring container which is part of the application.) Page 26 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP6 - Blueprint service-bundle examplesBilling service bundle<blueprint> <service ref=”service” interface = ”org.example.bill.BillingService” /> <bean id=”service” scope=”prototype” class=”org.example.bill.impl.BillingServiceImpl” /> Billing</blueprint> -“prototype” scope indicates a new instance is created by the container for each use.public interface BillingService { -“singleton” scope is the default. void bill(Order o);} Page 27 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP6 - Blueprint client-bundle examplese-Commerce bundle<blueprint> <bean id=”shop” class=”org.example.ecomm.ShopImpl”> <property name=”billingService” ref=”billingService” /> </bean> e-Commerce <reference id=”billingService” interface=”org.example.bill.BillingService” /></blueprint>public class ShopImpl { -injected service reference -service can change over timeprivate BillingService billingService; -can be temporarily absentvoid setBillingService(BillingService srv) { billingService = srv; without the bundle caring } -managed by Blueprint containervoid process(Order o) { billingService.bill(o); }} Page 28 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP7 – Make Bundles LooselyCoupled & Highly Cohesive FileSystemAPI SomeotherAPI TransactionsAPI API Implementation org.hal.log.impl org.hal.log.api org.hal.log.impl org.hal.fslog.impl DBAPI JPAAPI Hairball effect – one bundle has many package dependenciesFigure 9. Poorly purposed system where a single bundle provides multiple implementations of the same API Page 29 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

BP7 – Make Bundles LooselyCoupled & Highly Cohesive FileSystemAPI API Implementation org.hal.log.api org.hal.fslog.impl Implementation Implementation Implementation org.hal.DBlog.impl org.hal.DBlog.impl org.hal.DBlog.impl DBAPI DBAPI DBAPI Figure 10. A well purposed system where each implementation of an API is provided by a separate bundlePage 30 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

Summary – OSGi Best Practices> BP1 - Use Import-Package instead of Require-Bundle> BP2 - Avoid split packages> BP3 - Version bundles and packages> BP4 - Separate API from implementations> BP5 - Share services not implementations> BP6 - Use Blueprint> BP7 - Make bundles loosely coupled & highly cohesive Page 31 OSGi Alliance © 2008-2011 . All Rights Reserved, 21.09.11 © IBM Corp. 2011

Quiz – What best practices are used? blog-apiWeb application bundle JNDI EM WEB-INF/ Blogging Blog META-INF/ web.xml Service OSGI-INF/blueprint/ persistence.xml blueprint.xml Persistence Service blog-servlet OSGI-INF/blueprint/ blog blueprint.xml blog-persistence Page 32 OSGi Alliance Community Event 2011© 2008-2011. All Rights Reserved, 21.09.11 © IBM Corp. 2011

Additional References OSGi Best Practiceswww.ibm.com/developerworks/websphere/techjournal/1007_charters/1007_charters.html Enterprise OSGi YouTube Channel: www.youtube.com/user/EnterpriseOSGi For more information on Enterprise OSGi take a look at Enterprise OSGi in Action : http://www.manning.com/cummins Page 34 OSGi Alliance Community Event 2011© 2008-2011. All Rights Reserved, 21.09.11 © IBM Corp. 2011

OSGi Best Practices - Tim Ward

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