ClassCastException using OSGi bundles in a Maven project

Question

I am quite a newbie with OSGi and struggeling with including bundles into my Maven project.

I created an API bundle and an implementation bundle using the mave-bundle-plugin. In my major project (a Maven project), I tried to get the service of the implemented bundle from a ServiceTracker using the Felix Framework. When I finally try to cast the obtained service into the correct type, I receive a ClassCastException.

API Maven project:

public interface ParserTestService {
    String validForStage();
}

API POM:

<artifactId>ParserTest</artifactId>
<version>0.0.2-SNAPSHOT</version>
<packaging>bundle</packaging>

<build>
    <plugins>
        <plugin> 
            <groupId>org.apache.felix</groupId>
            <artifactId>maven-bundle-plugin</artifactId>
            <extensions>true</extensions>
            <configuration>
                <instructions>
                    <Bundle-SymbolicName>${pom.groupId}.${pom.artifactId}</Bundle-SymbolicName>
                    <Bundle-Vendor>Apache-Felix</Bundle-Vendor>
                    <Bundle-Version>0.0.1</Bundle-Version>
                    <Export-Service>de.ParserTestService</Export-Service>    
                </instructions>
            </configuration>
        </plugin>
    </plugins>
</build>

<dependencies>
    <dependency>
        <groupId>org.apache.felix</groupId>
        <artifactId>org.apache.felix.framework</artifactId>
        <version>2.0.4</version>
    </dependency>
</dependencies>

Impl Maven project:

public class ParserImplService implements ParserTestService {
    public String validForStage() {
        return "S";
    }
}

Impl POM:

<artifactId>ParserTestVersion1</artifactId>
<version>0.0.2-SNAPSHOT</version>
<packaging>bundle</packaging>

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.felix</groupId>
            <artifactId>maven-bundle-plugin</artifactId>
            <extensions>true</extensions>
            <configuration>
                <instructions>
                    <Bundle-SymbolicName>${pom.groupId}.${pom.artifactId}</Bundle-SymbolicName>
                    <Bundle-Vendor>Apache-Felix</Bundle-Vendor>
                    <Bundle-Version>0.0.1</Bundle-Version>
                    <Bundle-Activator>de.Activator</Bundle-Activator>
                    <Export-Package>de</Export-Package>
                    <Export-Service>de.ParserImplService</Export-Service>
                    <Import-Package>org.osgi.framework</Import-Package>
                </instructions>
            </configuration>
        </plugin>
    </plugins>
</build>

<dependencies>
    <dependency>
        <groupId>org.apache.felix</groupId>
        <artifactId>org.apache.felix.framework</artifactId>
        <version>2.0.4</version>
        <type>bundle</type>
    </dependency>
    <dependency>
        <groupId>de</groupId>
        <artifactId>ParserTest</artifactId>
        <version>0.0.2-SNAPSHOT</version>
        <type>bundle</type>
    </dependency>
</dependencies>

Maven created two jar-files with the following Manifest files:

Manifest-Version: 1.0
Bnd-LastModified: 1340890655296
Build-Jdk: 1.6.0_24
Built-By: br_s1
Bundle-ManifestVersion: 2
Bundle-Name: Parser Test Interface
Bundle-SymbolicName: de.ParserTest
Bundle-Vendor: Apache-Felix
Bundle-Version: 0.0.1
Created-By: Apache Maven Bundle Plugin
Export-Package: de;version="0.0.1"
Export-Service: de.ParserTestService
Tool: Bnd-1.50.0

Manifest-Version: 1.0
Bnd-LastModified: 1340890661890
Build-Jdk: 1.6.0_24
Built-By: br_s1
Bundle-Activator: de.Activator
Bundle-ManifestVersion: 2
Bundle-Name: Parser Test
Bundle-SymbolicName: de.ParserTestVersion1
Bundle-Vendor: Apache-Felix
Bundle-Version: 0.0.1
Created-By: Apache Maven Bundle Plugin
Export-Package: de;version="0.0.1"
Export-Service: de.ParserImplService
Import-Package: org.osgi.framework;version="[1.5,2)"
Tool: Bnd-1.50.0

In my Major Maven project, I setup and started a Felix framework. In the subfolder "bundles", I copied the jar-files created by the Maven deployment process above. In the install-routine, I tried to install these bundles and start them:

public class HostActivator implements BundleActivator {
...
    public BundleContext getContext()
    {
        return m_context;
    }
...
}

public class HostApplication
{
    private HostActivator m_activator = null;
    private Felix m_felix = null;
    private ServiceTracker m_tracker = null;

    public HostApplication()
    {
        Map<String, Object> configMap = new HashMap<String, Object>();
        configMap.put(Constants.FRAMEWORK_SYSTEMPACKAGES_EXTRA, "de.test; version=1.0.0");
        m_activator = new HostActivator();
        List<BundleActivator> list = new ArrayList<BundleActivator>();
        list.add(m_activator);
        configMap.put(FelixConstants.SYSTEMBUNDLE_ACTIVATORS_PROP, list);

        m_felix = new Felix(configMap);
        m_felix.start();

        m_tracker = new ServiceTracker(m_activator.getContext(), ParserTestService.class.getName(), null);
        m_tracker.open();
    }

    public void installBundlesFromDir() {

        File dir = new File("bundles");
        for (File f : dir.listFiles()) {
            try {
                Bundle b = m_felix.getBundleContext().installBundle("file:"+f.getAbsolutePath());
                b.start();

                ServiceReference sr = m_felix.getBundleContext().getServiceReference(ParserTestService.class.getName());

                ParserTestService service = (ParserTestService) m_felix.getBundleContext().getService(sr);

            } catch (BundleException e) {
                System.err.println("could not load bundle "+f.getAbsolutePath());
            }
        }        

    }
}

The corresponding POM:

<artifactId>parserUse</artifactId>
<version>0.0.1-SNAPSHOT</version>

<dependencies>
    <dependency>
        <groupId>org.apache.felix</groupId>
        <artifactId>org.apache.felix.framework</artifactId>
        <version>2.0.4</version>
    </dependency>            
    <dependency>
        <groupId>de</groupId>
        <artifactId>ParserTestVersion1</artifactId>
        <version>0.0.2-SNAPSHOT</version>
    </dependency>
    <dependency>
        <groupId>de</groupId>
        <artifactId>ParserTest</artifactId>
        <version>0.0.2-SNAPSHOT</version>
    </dependency>
</dependencies>

When I try to call the install routine, however, I receive a ClassCastException:

java.lang.ClassCastException: de.ParserImplService cannot be cast to de.ParserTestService

I already checked the class loaders

ParserTestService.class.getClassLoader()

and

(m_felix.getBundleContext().getService(sr)).getClass().getClassLoader()

and they are different from each other.

I always have thought OSGi would take care of the class loading for me.

Does anyone has a clue what I am doing wrong? Any help is appreciated!

Thanks in advance, Sebastian

Answer 1

I finally found a way to solve this problem, but only by avoiding Felix and using Equinox instead.

1.) The API exports only the package <Export-Package>de</Export-Package>

2.) The Impl exports nothing. It only defines the activator and its imports

<Bundle-Activator>de.Activator</Bundle-Activator>
<Import-Package>org.osgi.framework;de</Import-Package>

3.) I replaced the whole HostApplication using Equinox:

public class HostApplication {
    private BundleContext bundleContext;

    public HostApplication(String profileName) {
        BundleContext bc = null;
        Properties frameworkProperties = readCustomProfile(profileName);

        frameworkProperties.put("osgi.clean", "true");
        frameworkProperties.put("osgi.console", "true");

        Map<String, String> frameworkPropertiesMap = new HashMap<String, String>();
        for (Object o : frameworkProperties.keySet()) {
            frameworkPropertiesMap.put((String) o,
                    (String) frameworkProperties.getProperty((String) o));
        }

        EclipseStarter.setInitialProperties(frameworkPropertiesMap);
        bc = EclipseStarter.startup(new String[] { "-console", "-dev", "bin" },    null);
    }

   public boolean containsIegm(String stage, byte[] msg) {

        try {
            ServiceReference serviceReference = bundleContext.getServiceReference(ParserTest.class.getName());
            return ((ParserImplService) bundleContext.getService(serviceReference)).containsIegm(msg);

        } catch (Exception ex) {
            ex.printStackTrace();
        }

        return false;
    }

    public void installBundlesFromDir() {

        File dir = new File("bundles");
        int i = 0;
        for (File f : dir.listFiles()) {
            try {
                Bundle b = bundleContext.installBundle("file:"+ f.getAbsolutePath());
                b.start();
            } catch (BundleException e) {
                System.err.println("could not load bundle "    + f.getAbsolutePath());
            }
        }

    }
}

I tried exactly the same with Felix by using the BundleContext of m_felix (see question) and removed the HostActivator completly (I know realize it is not necessary in my app). However, I could not make it work.

Anyways, with Equinox it is equally easy to embedd an OSGi framework in non-OGSi/non-bundle applications.

Thanks everyone for their help! Sebastian

Answer 2

Both bundles are exporting "de". This means that there will be two name spaces called "de".
The bundle Bundle-SymbolicName: de.ParserTestVersion1 should import "de" and get it from the other bundle