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