Ada's Programming Notebook: java.lang.NullPointerException: A null service reference is not allowed.

Problem: When trying to get a service from the BundleContext, NullPointerException is found.

public class Activator implements BundleActivator {
    ServiceReference helloServiceReference;
    public void start(BundleContext context) throws Exception {
        System.out.println("Hello World!!");
        helloServiceReference= context.getServiceReference(HelloService.class.getName());
        HelloService helloService =(HelloService)context.getService(helloServiceReference);
        System.out.println(helloService.sayHello());

    }
    public void stop(BundleContext context) throws Exception {
        System.out.println("Goodbye World!!");
        context.ungetService(helloServiceReference);
    }
}

org.osgi.framework.BundleException: Exception in com.javaworld.sample.helloworld.Activator.start() of bundle com.javaworld.sample.HelloWorld. at org.eclipse.osgi.framework.internal.core.BundleContextImpl.startActivator(BundleContextImpl.java:734) at org.eclipse.osgi.framework.internal.core.BundleContextImpl.start(BundleContextImpl.java:683) at org.eclipse.osgi.framework.internal.core.BundleHost.startWorker(BundleHost.java:381) at org.eclipse.osgi.framework.internal.core.AbstractBundle.resume(AbstractBundle.java:389) at org.eclipse.osgi.framework.internal.core.Framework.resumeBundle(Framework.java:1131) at org.eclipse.osgi.framework.internal.core.StartLevelManager.resumeBundles(StartLevelManager.java:559) at org.eclipse.osgi.framework.internal.core.StartLevelManager.resumeBundles(StartLevelManager.java:544) at org.eclipse.osgi.framework.internal.core.StartLevelManager.incFWSL(StartLevelManager.java:457) at org.eclipse.osgi.framework.internal.core.StartLevelManager.doSetStartLevel(StartLevelManager.java:243) at org.eclipse.osgi.framework.internal.core.StartLevelManager.dispatchEvent(StartLevelManager.java:438) at org.eclipse.osgi.framework.internal.core.StartLevelManager.dispatchEvent(StartLevelManager.java:1) at org.eclipse.osgi.framework.eventmgr.EventManager.dispatchEvent(EventManager.java:230) at org.eclipse.osgi.framework.eventmgr.EventManager$EventThread.run(EventManager.java:340) Caused by: java.lang.NullPointerException: A null service reference is not allowed. at org.eclipse.osgi.framework.internal.core.BundleContextImpl.getService(BundleContextImpl.java:586) at com.javaworld.sample.helloworld.Activator.start(Activator.java:20) at org.eclipse.osgi.framework.internal.core.BundleContextImpl$1.run(BundleContextImpl.java:711) at java.security.AccessController.doPrivileged(AccessController.java:251) at org.eclipse.osgi.framework.internal.core.BundleContextImpl.startActivator(BundleContextImpl.java:702) ... 12 more

Cause:

The ServiceReference can be null if no HelloService is registered, resulting in NullPointerException on line 6.
The HelloService object cannot be got, due to missing permissions, possible timing issues if the HelloService unregisters between lines 5 and 6, causing NullPointerException on line 6.
The HelloService may have become unusable, resulting in any RuntimeException subclass, most likely IllegalStateException on line 6.

Solution: Use ServiceTracker instead.

References

OSGi Service

Ada's Programming Notebook

21 Mar 2013

java.lang.NullPointerException: A null service reference is not allowed.

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