[CHAIN-51] Add a possibility for listening for events during command execution

• Type: New Feature
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: API
• Assignee: Unassigned
• Reporter: Santiago Basulto
• Created: 06/Sep/10 16:47
• Updated: 04/Jul/13 19:26

Description

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.