Apache Felix - Example 3 Continued: Testing Service Unregistration

Apache Felix Tutorial Example 3 walks the user through an implementation of a simple dictionary service. At the end of the tutorial, it describes a use case in which the dictionary service is unregistered. Under this scenario, the code in the example should throw a null pointer exception.

 I was curious how to force this use case and came up with the following additional steps to experiment with unregistering the service while the client was using it. We just need access to another shell so that we can have the client running in one shell, and stop the service in a second shell.

1. Begin, by downloading the Remote Shell bundle under the subprojects section of the download page.
2. Install and start the Remote Shell bundle. This will provide remote access to the Felix shell via Telnet.

   start file:/path/to/download/org.apache.felix.shell.remote-1.1.2.jar
   

3. Open your preferred Telnet application, such as putty, and set the port to 6666 and the host to localhost.
4. In your original shell (not the remote) start the example 3 client.

   g! lb | grep Client
   START LEVEL 1
      ID|State      |Level|Name
      12|Resolved   |    1|Dictionary Client (1.0.0)
   g! start 12
   Enter a blank line to exit.
   Enter a word:
   testing
   No match found!
   

5. Find the ID of the English dictionary service and stop it.

   g! lb | grep English
    10|Resolved  |   1|English dictionary (1.0.0)
   g! stop 10
   

6. Lastly, go back to the shell running the dictionary client and enter a new word. You should now receive a null pointer exception!

   Enter a word:
   testing2
   org.osgi.framework.BundleException: Activator start error in bundle [12].
           at org.apache.felix.framework.Felix.activateBundle(Felix.java:2027)
           at org.apache.felix.framework.Felix.startBundle(Felix.java:1895)
           at org.apache.felix.framework.BundleImpl.start(BundleImpl.java:944)
           at org.apache.felix.gogo.command.Basic.start(Basic.java:729)
           at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
           at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
           at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
           at java.lang.reflect.Method.invoke(Unknown Source)
           at org.apache.felix.gogo.runtime.Reflective.invoke(Reflective.java:137)
           at org.apache.felix.gogo.runtime.CommandProxy.execute(CommandProxy.java:82)
           at org.apache.felix.gogo.runtime.Closure.executeCmd(Closure.java:477)
           at org.apache.felix.gogo.runtime.Closure.executeStatement(Closure.java:403)
           at org.apache.felix.gogo.runtime.Pipe.run(Pipe.java:108)
           at org.apache.felix.gogo.runtime.Closure.execute(Closure.java:183)
           at org.apache.felix.gogo.runtime.Closure.execute(Closure.java:120)
           at org.apache.felix.gogo.runtime.CommandSessionImpl.execute(CommandSessionImpl.java:89)
           at org.apache.felix.gogo.shell.Console.run(Console.java:62)
           at org.apache.felix.gogo.shell.Shell.console(Shell.java:203)
           at org.apache.felix.gogo.shell.Shell.gosh(Shell.java:128)
           at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
           at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
           at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
           at java.lang.reflect.Method.invoke(Unknown Source)
           at org.apache.felix.gogo.runtime.Reflective.invoke(Reflective.java:137)
           at org.apache.felix.gogo.runtime.CommandProxy.execute(CommandProxy.java:82)
           at org.apache.felix.gogo.runtime.Closure.executeCmd(Closure.java:477)
           at org.apache.felix.gogo.runtime.Closure.executeStatement(Closure.java:403)
           at org.apache.felix.gogo.runtime.Pipe.run(Pipe.java:108)
           at org.apache.felix.gogo.runtime.Closure.execute(Closure.java:183)
           at org.apache.felix.gogo.runtime.Closure.execute(Closure.java:120)
           at org.apache.felix.gogo.runtime.CommandSessionImpl.execute(CommandSessionImpl.java:89)
           at org.apache.felix.gogo.shell.Activator.run(Activator.java:75)
           at java.lang.Thread.run(Unknown Source)
   Caused by: java.lang.NullPointerException
           at com.gastongonzalez.felix.tutorial.example3.Activator.start(Unknown Source)
           at org.apache.felix.framework.util.SecureAction.startActivator(SecureAction.java:641)
           at org.apache.felix.framework.Felix.activateBundle(Felix.java:1977)
           ... 32 more
   java.lang.NullPointerException
   

Apache Felix - Bundle Installation and NoClassDefFoundError

I am on day two of a long journey to master OSGi. As such, I have been working through the OSGi tutorials on the Apache Felix site. As I continue down this path, I thought I would document the issues that I encounter as a novice, hopefully, helping others at my same level.

This afternoon, I tried installing a new bundle (felix-tutorial-example5.jar) and received a java.lang.NoClassDefFoundError exception for the ServiceTracker class. As it turns out, I forgot to import the org.osgi.util.tracker package in my manifest. So next time you receive a NoClassDefFoundError exception when installing a bundle, check that you have all of your import packages defined.

The Solution:

Import-Package: org.osgi.framework, 
 org.osgi.util.tracker,
 com.gastongonzalez.felix.tutorial.example2.service

The Problem:

g! felix:start file:/c:/temp/felix-tutorial-example5.jar
org.osgi.framework.BundleException: Activator start error in bundle [28].
        at org.apache.felix.framework.Felix.activateBundle(Felix.java:2027)
        at org.apache.felix.framework.Felix.startBundle(Felix.java:1895)
        at org.apache.felix.framework.BundleImpl.start(BundleImpl.java:944)
        at org.apache.felix.gogo.command.Basic.start(Basic.java:729)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at org.apache.felix.gogo.runtime.Reflective.invoke(Reflective.java:137)
        at org.apache.felix.gogo.runtime.CommandProxy.execute(CommandProxy.java:82)
        at org.apache.felix.gogo.runtime.Closure.executeCmd(Closure.java:477)
        at org.apache.felix.gogo.runtime.Closure.executeStatement(Closure.java:403)
        at org.apache.felix.gogo.runtime.Pipe.run(Pipe.java:108)
        at org.apache.felix.gogo.runtime.Closure.execute(Closure.java:183)
        at org.apache.felix.gogo.runtime.Closure.execute(Closure.java:120)
        at org.apache.felix.gogo.runtime.CommandSessionImpl.execute(CommandSessionImpl.java:89)
        at org.apache.felix.gogo.shell.Console.run(Console.java:62)
        at org.apache.felix.gogo.shell.Shell.console(Shell.java:203)
        at org.apache.felix.gogo.shell.Shell.gosh(Shell.java:128)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
        at java.lang.reflect.Method.invoke(Unknown Source)
        at org.apache.felix.gogo.runtime.Reflective.invoke(Reflective.java:137)
        at org.apache.felix.gogo.runtime.CommandProxy.execute(CommandProxy.java:82)
        at org.apache.felix.gogo.runtime.Closure.executeCmd(Closure.java:477)
        at org.apache.felix.gogo.runtime.Closure.executeStatement(Closure.java:403)
        at org.apache.felix.gogo.runtime.Pipe.run(Pipe.java:108)
        at org.apache.felix.gogo.runtime.Closure.execute(Closure.java:183)
        at org.apache.felix.gogo.runtime.Closure.execute(Closure.java:120)
        at org.apache.felix.gogo.runtime.CommandSessionImpl.execute(CommandSessionImpl.java:89)
        at org.apache.felix.gogo.shell.Activator.run(Activator.java:75)
        at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NoClassDefFoundError: org/osgi/util/tracker/ServiceTracker
        at com.gastongonzalez.felix.tutorial.example5.Activator.start(Unknown Source)
        at org.apache.felix.framework.util.SecureAction.startActivator(SecureAction.java:641)
        at org.apache.felix.framework.Felix.activateBundle(Felix.java:1977)
        ... 32 more
Caused by: java.lang.ClassNotFoundException: org.osgi.util.tracker.ServiceTracker not found by[28]
        at org.apache.felix.framework.BundleWiringImpl.findClassOrResourceByDelegation(BundleWiringImpl.java:1460)
        at org.apache.felix.framework.BundleWiringImpl.access$400(BundleWiringIm
pl.java:72)
        at org.apache.felix.framework.BundleWiringImpl$BundleClassLoader.loadCla
ss(BundleWiringImpl.java:1843)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        ... 35 more
java.lang.NoClassDefFoundError: org/osgi/util/tracker/ServiceTracker