stateful command pattern

I was wondering what is the best way to represent an edit form in the context of domain model and I ended up with the command design pattern.

According to this: Using Command Design pattern commands should be immutable which is not what I need - I need stateful command with edi开发者_Go百科table parameters (the whole command will be edited in ui/form)

Why is it considered to be bad to have stateful command?

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EDIT: After some time it is now clear I was looking for the ViewModel pattern. That is the appropriate way to model any webapp screen. Basically it is stateful (per view instance) controller.

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You still want them to be immutable, because they can then be used to recreate the current state from a snapshot. But they can have all the parameters you want, as long as you make sure they cannot change after applying the command.

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if you want it mutable i would suggest using a FlyWeight Pattern instead. You can make it similar to a command pattern since its a hash of objects and it reuses the same objects if they exist already thus persisting the objects state.

You can think of FlyWeight as a group of singleton objects you can call on the fly (by a hash function).

So a flyweightfactory would house all your objects in a hash map and you could use the factory to retrieve the object maintaining its state.

http://www.avajava.com/tutorials/lessons/flyweight-pattern.html --> for anyone's reference.