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From "Niall Pemberton (JIRA)" <j...@apache.org>
Subject [jira] Updated: (CHAIN-51) New Features for the project.
Date Wed, 15 Sep 2010 14:56:32 GMT

     [ https://issues.apache.org/jira/browse/CHAIN-51?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Niall Pemberton updated CHAIN-51:
---------------------------------

    Attachment: CHAIN-51-Alternative-Listener-proposal.patch

I have some comments about your suggestions - but before that Commons Chain is pretty dormant
- I did the last bugfix release back in May 2008, but Chain hasn't had any real development
since at least 2006. It would probably be a good idea to try to find a committer willing to
commit your work, before putting any  more effort on this - otherwise you may be wasting your
time. Having said that, here are my comments.

There is some general work needed to your contribution before it would be ready to commit.
If you fixed them and re-submitted, then it would reduce the work needed to be done by a committer
and probably increase the chances that it would be accepted:
    * Create a patch (rather than rar file) - see http://commons.apache.org/patches.html
    * Change the package names from your "ar.com.santiagobasulto" to "org.apache.commons.chain"
    * Add the ASF license headers to your source files: http://www.apache.org/legal/src-headers.html
    * The tests are currently mixed in with the rest of the source code - move them to follow
the commons chain directory structure (tests are in "src/test/java") and make them JUnit tests
like the rest of Chain's tests

In its current form your contribution requires a minimum of JDK 1.6 and Commons Chain is currently
supporting a minimum of JDK 1.3. Changing the minimum JDK version is probably  not going to
be an issue - but the only thing in your work that requires JDK 1.6 rather than JDK 1.5 is
the  use of @Override markers for implementations of interfaces (which JDK 1.5 doesn't allow).
I think JDK 1.5 would be a good minimum version and removing @Override for interface implementations
would not be a great loss.

I have some comments about the implementation in general - apologies, they are probably disorganized
and some may contradict others(!) - but here goes:
    * I would drop the PaneHandler and StreamHandler implementations - I think those implementations
are too specific for a Commons component and don't add enough value to be included
    * I don't like the way the new Action interface extends the existing Command interface
- which then requires a new ActionChain interface to provide the Chain equivalent. IMO it
would be better to have this as a completely separate interface that any Command or Chain
could implement. To make that workable requires adding a "get" method for the handler/listeners

    * I think it would be better to use the java's  "listener" concept
        * rename Action to CommandHandler and
        * rename ActionHandler to CommandListener and extend the EventListener marker interface
        * Create a CommandEvent object that extends EventObject and is used as a parameter
to the listener methods
        * Remove the "fail" method from the listener and add "Exception" as a property of
CommandEvent. The "done" method then gets called whether the execution is successful or throws
an exception.
    * We could then modify the existing ChainBase to implement CommandHandler and call listeners
for itself and for the Commands it executes. This way anything using ChainBase would get this
automatically built in

{code}
public interface CommandHandler {
	void addListener(CommandListener c);
	boolean removeListener(CommandListener c);
	Iterable<CommandListener> getListeners();
}
{code}

{code}
public interface CommandListener extends EventListener {
	void start(CommandEvent event);
	void finish(CommandEvent event);
}
{code}


{code}
public class CommandEvent extends EventObject {

    private final Context context;
    private final Exception exception;

    public CommandEvent(Command command, Context context, Exception exception) {
        super(command);
        this.context = context;
        this.exception = exception;
    }

    public Context getContext() {
        return context;
    }

    public Exception getException() {
        return exception;
    }

}
{code}


> New Features for the project.
> -----------------------------
>
>                 Key: CHAIN-51
>                 URL: https://issues.apache.org/jira/browse/CHAIN-51
>             Project: Commons Chain
>          Issue Type: New Feature
>            Reporter: Santiago Basulto
>         Attachments: actions-src.rar, CHAIN-51-Alternative-Listener-proposal.patch
>
>   Original Estimate: 240h
>  Remaining Estimate: 240h
>
> I'm proposing a change to the project. Did not know how to do it, so asked in the mailing
list and told me to make the proposal here.
> I'll comment a little about my changes. It needs a lot of refactoring and documenting,
but i'd like to comment the main idea behind it, so you can give your opinion. I have faced
some problems with names. I did not want to rename commons.chain classes, as a matter of respect,
so some names can seem weird, it can change.
> First of all, i needed more "control" over my commands. I like to have everything logged,
and several commands were used in GUI apps, so i needed more User interaction. Then, i decide
to provide the main Interface (Command) some other methods, just to can track what is it doing.
I made a new interface called Action (i use the other name given to this pattern). I extend
it from Command, just becouse i didn't want to change everything, and can keep using my old
Commands.
> This new Interface, Action, has two new methods:
> 	void registerHandler(ActionHandler c);
> 	boolean removeHandler(ActionHandler c); //true if the handler was present, false otherwise
> The main idea behind this was to have a Handler object that can track the "moves and
states" of the Action (or Command) class. It's something similar to the Observer Pattern.
An action "can" (optionally, if doesn't want to register a handler, it's a simple Command)
register a Handler, and comunicate things about itself. So, i have an Interface called ActionHandler.
It has three methods: 
> 	
> 	void start(Action a);
> 	void done(Action a);
> 	void fail(Action a,Exception e);
> Then, for example, the action "can" invoke start method from its handler, to comunicate
it that has started executing. It's really simple, but helped me big time.
> Something great about the Action Interface, is that it only sais that you can register
a handler, not the number of handlers. So, a Class implementing Action can register a number
of handlers (file logger handler, GUI tool for comunicating the user, console logger, etc)
and inform about the progress to all of them. If it's not needed to comunicate, this class
can just execute silently.
> So, this is the main change, but with this little change i needed to do something with
the chain. So i just made the Chain interface extend the Action interface. Of course, can
be another class, something like ActionChain that implements the Action Interface, and let
Chain untouched.
> I've attached a simpler version of my source code. With just the basic classes and a
package for test it. I've developed some other classes, for example, Action implementations
that register several ActionHandlers. I'm currently working on a "BlockingQueueChain", it's
a chain that can execute all its Commands (or Actions) in parallel. Obviusly, there are not
so many cases when this Chain can be used. If someone is interested i will can send the source
code.
> Ok, i think that's all. Hope you can tell me if this is a good idea, or not. Or simply,
whether i should start a new "branch" of the project to no interfere with Commons Chain.

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