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From Wilder Rodrigues <>
Subject Re: [DISCUSS] Moving to Java 8
Date Thu, 30 Apr 2015 19:55:05 GMT
Hi Marcus,

Apologies for taking so much time to reply to your email, but was, and still am, quite busy.

I would only use reflection if that was the only way to do it. The use of reflection usually
makes the code more complex, which is not good when we have java developers in all different
levels (from jr. do sr) working with cloudstack. It also makes us lose the type safety, which
might also harm the exception handling if not done well. In addition, if we need to refactor
something, the IDE is no longer going to do few things because the refection code cannot be

If someone will need to extend the LibvirtComputingResource that would be no problem with
the approach I’m using. The CitrixResourceBase also has quite few sub-classes and it works
just fine.

I will document on the wiki page how it should be done when sub-classing the LibvirtComputingResource

In a quick note/snippet, one would do:

public class EkhoComputingResource extends LibvirtComputingResource {

    public Answer executeRequest(final Command cmd) {

        final LibvirtRequestWrapper wrapper = LibvirtRequestWrapper.getInstance();
        try {
            return wrapper.execute(cmd, this);
        } catch (final Exception e) {
            return Answer.createUnsupportedCommandAnswer(cmd);

In the flyweight where I keep the wrapper we could have ():

        final Hashtable<Class<? extends Command>, CommandWrapper> linbvirtCommands
= new Hashtable<Class<? extends Command>, CommandWrapper>();
        linbvirtCommands.put(StopCommand.class, new LibvirtStopCommandWrapper());

        final Hashtable<Class<? extends Command>, CommandWrapper> ekhoCommands
= new Hashtable<Class<? extends Command>, CommandWrapper>();
        linbvirtCommands.put(StopCommand.class, new EkhoStopCommandWrapper());

        resources.put(LibvirtComputingResource.class, linbvirtCommands);
        resources.put(EkhoComputingResource.class, ekhoCommands);

But that is needed only if the StopCommand has a different behaviour for the EkhoComputingResource.

Once a better version of the documentation is on the wiki, I will let you know.

On other matters, I’m also adding unit tests for all the changes. We already went from 4%
to 13.6% coverage in the KVM hypervisor plugin. The code I already refactored has 56% of coverage.

You can see all the commits here:


On 23 Apr 2015, at 17:26, Marcus <<>>

Great to see someone working on it. What sorts of roadblocks came out
of reflection? How does the wrapper design solve the pluggability
issue? This is pretty important to me, since I've worked with several
companies now that end up subclassing LibvirtComputingResource in
order to handle their own Commands on the hypervisor from their
server-side plugins, and changing their 'resource' to that in Since the main agent class needs to be set at agent
join, this is harder to manage than it should be.

I mentioned the reflection model because that's how I tend to handle
the commands when subclassing LibvirtComputingResource. I haven't had
any problems with it, but then again I haven't tried to refactor 5500
lines into that model, either.

On Thu, Apr 23, 2015 at 1:17 AM, Wilder Rodrigues
<<>> wrote:
Hi Marcus,

I like the annotation idea, but reflection is trick because it hides some
information about the code.

Please, have a look at the CitrixResourceBase after the refactor I did. It
became quite smaller and test coverage was improved.


The same patter is being about to Libvirt stuff. The coverage on the KVM
hypervisor plugin already went from 4 to 10.5% after refactoring 6 commands


On 22 Apr 2015, at 23:06, Marcus <> wrote:

Kind of a tangent, but I'd actually like to see some work done to
clean up LibvirtComputing resource. One model I've prototyped that
seems to work is to create an annotation, such as
'KVMCommandExecutor', with a 'handles' property. With this annotation,
you implement a class that handles, e.g. StartCommand, etc. Then in
LibvirtComputingResource, the 'configure' method fetches all of these
executors via reflection and stores them in an object. Then, instead
of having all of the 'instanceof' lines in LibvirtComputingResource,
the executeRequest method fetches the executor that handles the
incoming command and runs it.

I think this would break up LibvirtComputingResource into smaller,
more testable and manageable chunks, and force things like config and
utility methods to move to a more sane location, as well. As a bonus,
this model makes things pluggable. Someone could ship KVM plugin code
containing standalone command executors that are discovered at runtime
for things they need to run at the hypervisor level.

On Tue, Apr 21, 2015 at 6:27 AM, Wilder Rodrigues
<> wrote:

Hi all,

Yesterday I started working on the LibvirtComputingResource class in order
to apply the same patterns I used in the CitrixResourceBase + add more unit
tests to it After 10 hours of work I got a bit stuck with the 1st test,
which would cover the refactored LibvirtStopCommandWrapper. Why did I get
stuck? The class used a few static methods that call native libraries, which
I would like to mock. However, when writing the tests I faced problems with
the current Mockito/PowerMock we are using: they are simply not enough for
the task.

What did I do then? I added a dependency to EasyMock and PowerMock-EasyMock
API. It worked almost fine, but I had to add a “-noverify” to both my
Eclipse Runtime configuration and also to the
cloud-plugin-hypervisor-kvm/pom.xml file. I agree that’s not nice, but was
my first attempt of getting it to work. After trying to first full build I
faced more problems related to ClassDefNotFoundExpcetion which were
complaining about Mockito classes. I then found out that adding the
PowerMockRunner to all the tests classes was going to be a heavy burden and
would also mess up future changes (e.g. the -noverify flag was removed from
Java 8, thus adding it now would be a problem soon).

Now that the first 2 paragraphs explain a bit about the problem, let’s get
to the solution: Java 8

The VerifyError that I was getting was due to the use of the latest EasyMock
release (3.3.1). I tried to downgrade it to 3.1/3.2 but it also did not
work. My decision: do not refactor if the proper tests cannot be added. This
left me with one action: migrate to Java 8.

There were mentions about Java 8 in february[1] and now I will put some
energy in making it happen.

What is your opinion on it?

Thanks in advance.


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