OSGi Enablement For Apache Tuscany
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OSGi Enablement For Apache Tuscany

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OSGi Enablement for Apache Tuscany

OSGi Enablement for Apache Tuscany

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OSGi Enablement For Apache Tuscany OSGi Enablement For Apache Tuscany Presentation Transcript

  • OSGi Enablement for Apache Tuscany Raymond Feng [email_address]
  • Overview
  • Motivations
    • Provide modularity for Tuscany to formalize/enforce the SPI contracts and minimize the package dependencies across modules
    • Enable Tuscany to work with OSGi environment such as JEE application servers, Eclipse RCP or Spring DM
    • Provide versioning and isolation so that Tuscany extensions can depend on different versions of the same library
    • Provide lifecycle management for extensions: install/uninstall/start/stop a module
    View slide
  • Objectives
    • Tuscany runtime will be able to run in both non-OSGi and OSGi environment
      • No OSGi APIs should be used for non-OSGi specific modules
    • Build a consistent OSGi story to facilitate developing, building, launching, running and testing Tuscany
      • Makes developers’ life a bit easier to work with OSGi
    View slide
  • What problems do we try to solve?
    • Turning Tuscany modules into OSGi bundles
    • Turning 3 rd party dependencies into OSGi bundles
    • Developing, building, launching, running and testing with OSGi
    • Producing distributions that are compatible with the OSGi bundle structure in an efficient way (in one-two minutes)
  • Turning Tuscany modules into OSGi bundles
  • Creating bundles for Tuscany modules
    • Modularize Tuscany after the maven modules
      • One OSGi bundle per maven module
      • Be consistent for build, packaging and runtime
      • Much easier to aggregating than decomposing
    • Developers are responsible for authoring and maintaining MANIFEST.MF (instead of MF generation tools)
      • Tooling friendly
      • Developers pay more attentions to the dependencies
  • Things to consider to create an OSGi bundle for a module
    • Add META-INF/MANIFEST.MF (don’t stop here …)
    • Clean up module dependencies and package visibilities
    • Prepare for code changes
      • Service Discovery
      • ClassLoading
  • Rules of thumb
    • Identify the absolutely necessary SPI packages that need to be exported
      • Don't try to export everything
      • For model modules, try to only export the package that contains the interfaces
      • Try not to export any package from the xxx-runtime moudles
      • Any classes that can be accessed via the ExtensionPointRegistry using interfaces should not be exported
    • Only import other packages when it's needed
      • For example, we used to have a lot of modules pull in assembly for just a constant for the SCA namespace
      • Avoid DynamicImport-Package=*
      • Avoid Require-Bundle
    • Do not export "private" packages as a workaround or hack which can fail the "clean SPI". Refactor things into SPIs if necessary
  • Granularity Discussion
    • 180+ bundles cumbersome
    • Multiple bundles required to enable one capability
    • Much debate about right level of granularity (flexibility vs. usability)
    • Some opinions
      • Fine-grained bundles suitable for developer view
      • Features/Profiles used to “group” bundles to provide a user view
        • Inspired by Eclipse Features
  • Dealing with 3 rd party jars
  • Handling 3 rd party jars
    • We have to live with the reality:
      • Many 3 rd party jars are not OSGi bundles. No repo is available to get all converted bundles
        • We need to convert them (build time, run time)
      • Some of the 3 rd party bundles are broken (w/ bogus MF)
        • We need to fix them (replacing the MF)
      • More and more 3 rd party jars are upgraded to be OSGi bundles
        • We should be able to incrementally consume 3 rd party jars as OSGi bundles
  • Converting 3 rd party jars to OSGi bundles
    • A folder bundle is created to represent a 3 rd party jar
    • The folder structure looks like:
      • jaxb-impl-2.1.12
        • META-INF
          • MANIFEST.MF
        • jaxb-impl-2.1.12.jar
    • It is non-invasive and flexible
      • The original jar is not changed (avoid legal, signature issues)
      • Multiple jars can be easily aggregated (control the bundle granularity)
      • The MANIFEST.MF can be easily customized
    third-party.jar MANIFEST Bundle-Classpath: third-party.jar Dynamic-Import-Package: * Export-Package: ... ... third-party.jar Install OSGi Framework third-party-osgi.jar third-party.jar MANIFEST Bundle-Classpath: third-party.jar Import-Package: ... Export-Package: ... ...
  • Sample META-INF/MANIFEST.MF
    • Manifest-Version: 1.0
    • Bundle-ManifestVersion: 2
    • Bundle-SymbolicName: com.sun.xml.bind.jaxb-impl
    • Bundle-Name: com.sun.xml.bind.jaxb-impl
    • Bundle-Version: 2.1.12
    • DynamicImport-Package : javax.transaction;version="1.1",javax.transacti
    • on.xa;version="1.1",*
    • Bundle-ClassPath : jaxb-impl-2.1.12.jar
    • Export-Package : com.sun.xml.bind.v2.schemagen;version=2.1.12,com.sun.x
    • ml.bind.v2.util;version=2.1.12,com.sun.xml.txw2.annotation;version=2.
    • 1.12,com.sun.xml.bind.v2.model.runtime;version=2.1.12,com.sun.xml.bin
    • d.v2.runtime;version=2.1.12,com.sun.xml.txw2.output;version=2.1.12,co
    • m.sun.xml.bind.v2;version=2.1.12,com.sun.istack;version=2.1.12,com.su
    • n.xml.bind.v2.runtime.property;version=2.1.12,com.sun.xml.bind.v2.run
    • time.unmarshaller;version=2.1.12,com.sun.xml.bind.v2.model.nav;versio
    • n=2.1.12,com.sun.xml.bind.marshaller;version=2.1.12,com.sun.xml.bind.
    • v2.runtime.reflect.opt;version=2.1.12,com.sun.xml.bind.v2.runtime.out
    • put;version=2.1.12,com.sun.xml.txw2;version=2.1.12,com.sun.xml.bind.v
    • 2.schemagen.xmlschema;version=2.1.12,com.sun.xml.bind.v2.runtime.refl
    • ect;version=2.1.12,com.sun.xml.bind.v2.model.impl;version=2.1.12,com.
    • sun.xml.bind.unmarshaller;version=2.1.12,com.sun.xml.bind.util;versio
    • n=2.1.12,com.sun.xml.bind;version=2.1.12,com.sun.istack.localization;
    • version=2.1.12,META-INF.services;partial=true;mandatory:=partial,com.
    • sun.xml.bind.v2.model.annotation;version=2.1.12,com.sun.xml.bind.api.
    • impl;version=2.1.12,com.sun.xml.bind.api;version=2.1.12,com.sun.xml.b
    • ind.v2.model.core;version=2.1.12,com.sun.xml.bind.v2.bytecode;version
    • =2.1.12,com.sun.xml.bind.v2.schemagen.episode;version=2.1.12,com.sun.
    • xml.bind.annotation;version=2.1.12
  • Developing Tuscany with OSGi
  • Checking out source code and building with maven
    • Check out the Tuscany source code from SVN
      • svn co https://svn.apache.org/repos/asf/tuscany/java/sca/
    • Run maven build
      • mvn clean install -fn
    • Generate Eclipse projects
      • mvn -Peclipse
  • Setting up Eclipse PDE
    • Download Eclipse (w/ plugin development)
      • http://www.eclipse.org/downloads/download.php?file=/technology/epp/downloads/release/galileo/SR1/eclipse-jee-galileo-SR1-win32.zip
    • Configure PDE target platform
      • File  Open File
        • <tuscany>scadistributionall argetfeatures uscany-pde35.target
      • Click on “Set as target platform”
    • Load Tuscany modules into Eclipse
      • File  Import …  General  Import Existing Projects …
  • What’s happening during the Tuscany build?
    • Validating OSGi constraints to report bundle resolution issues during compilation
    • Generating PDE project so that Tuscany modules can be loaded in Eclipse to leverage the nice OSGi tooling
    • Generating OSGi bundles for 3 rd party jars
    • Generating PDE target platform definitions so that 3 rd party bundles can be used in Eclipse as plugin dependencies
    • Generating Equinox configuration so that Tuscany distribution can be directly loaded as an OSGi framework
  • Maven/OSGi Tools provided by Tuscany
    • Maven-bundle-plugin
      • Generates bundles for 3 rd party jars
      • Generates OSGi enabled PDE projects
      • Version 1.0.4 released at 10/09/2009
    • Maven-eclipse-compiler
      • Expose OSGi aware Eclipse JDT compiler
      • Expose Eclipse OSGi bundle validation
      • Version 1.0.1 released on 04/07/2009
    • Maven-osgi-junit-plugin
      • JUnit tests in a OSGi enabled environment
      • Version 1.0 released on 10/28/2009
    • https://svn.apache.org/repos/asf/tuscany/maven-plugins/trunk /
  • Development Time
    • Eclipse PDE provides nice OSGi tooling
      • Graphical editor for MANIFEST.MF (w/ additional tools to analyze/calculate dependencies)
      • Plugin Dependencies Classpath Container
      • Compilation errors/warning for OSGi constraint violations (w/ Quick Fix suggestions)
      • OSGi test environment to validate and launch OSGi framework (w/ console)
  • Runtime
    • Provide a SCA node launcher to start an OSGi runtime and run SCA application with the OSGi-enabled Tuscany runtime
    • We need to use Tuscany's service discovery mechanism to discover and instantiate the factories
        • Change how JDK factories such as XMLInputFactory, XPathFactory, and DocumentBuilderFactory, are discovered and instantiated
        • XMLInputFactory.newInstance() used the JSE service provider pattern which doesn't work with OSGi
    • Adjust the code that assumes there is a flat thread context classloader that can access all the classes in the Tuscany runtime
        • With OSGi, there is a network of classloaders (one classloader per module) and the class visibility is constrained by the OSGi headers such as Import-Package and Export-Package
        • The classloader for the current class is a good starting point for Class.forName() with OSGi
  • Launching OSGi framework within Eclipse PDE
  • Launching OSGi from Tuscany distribution
    • Equinox:
      • java -jar osgi-3.5.0-v20090520.jar -clean -console -configuration ..featuresconfiguration
    • http://cwiki.apache.org/confluence/display/TUSCANYxDOCx2x/Running+Tuscany+SCA+2.x+with+Equinox+and+Felix
  • Testing Tuscany with OSGi
  • A few options
    • Tuscany maven-osgi-junit plugin
      • Generate two bundles for the main and test classes respectively. The test bundle is a fragment of the main bundle.
        • For example, the plugin generates the following bundles for sample-calculator-osgi.jar: * sample-calculator-osgi-osgi.jar * sample-calculator-osgi-osgi-tests.jar
      • Find the EquinoxHost class from tuscany-node-launcher-equinox and create an instance
      • Start the equinox runtime
      • Set up the classloader for surefire so that it uses OSGi classloading for the test cases with the test bundle.
      • Delegate to surefire to run the unit tests
    • Apache Felix junit4osgi
      • http://felix.apache.org/site/apache-felix-ipojo-junit4osgi.html
  • Trouble-shooting OSGi related issues
  • Common traps
    • System packages need to be explicitly imported, such as javax.xml.namespace
    • Be careful of TCCL (ThreadContext Classloader)
      • No well-defined TCCL in OSGi
      • Equinox uses ContextFinder to find the closest class on the calling stack that is loaded by an OSGi bundle
      • JDK and some 3 rd party libraries uses service discover pattern relying on TCCL being able to load/see everything
  • Some tips
    • Most common exceptions:
      • ClassNotFoundException
      • NoClassDefFoundError
    • Bundle is not resolved:
      • Missing Import-Package (including system packages from the JDK)
      • Split package from Export-Package
      • Different versions of the same package are exported
      • Chain of bundle resolution (Exported packages from unresolved bundle cannot be seen.)
  • Useful Links
    • http://cwiki.apache.org/autoexport-2.2.9/TUSCANYxDOCx2x/osgi-enablement-for-tuscany-runtime.html
    • Infoq.com articles:
      • http:// www.infoq.com /articles/modular-java-what-is-it
      • http:// www.infoq.com /articles/modular-java-static-modularity
      • http://www.infoq.com/articles/modular-java-dynamic-modularity
    • http://www.dynamicjava.org/