FOR REVIEW: CURATOR-397, Strongly typed Model DSL

[Jordan Zimmerman <jo...@jordanzimmerman.com>]

Hey folks,

I have a new feature PR that needs review: https://github.com/apache/curator/pull/211 <https://github.com/apache/curator/pull/211>

This new feature allows code like this:

// let "client" be a CuratorFramework instance

ZPath path = ZPath.parse(...);    // whatever path you need
JacksonModelSerializer<Person> serializer = JacksonModelSerializer.build(Person.class);
ModeledAsyncCuratorFramework<MyModel> modeled = ModeledAsyncCuratorFramework.wrap(client, path, serializer);

...

public void writePerson(String id, Person p) {
    modeled.at(id).create(p);   // note this is an async operation
}

public void readPerson(String id, Consumer<Person> receiver) {
    modeled.at(id).read().whenComplete((person, exception) -> {
        if ( exception != null ) {
            ...
        } else {
            receiver.accept(person);
        }
    });
}
I've also added wrappers so that NodeCache, PathChildrenCache and TreeCache can have modeled usages.

E.g.

// given a model class "Person"

ModeledTreeCache<Person> cache = ModeledTreeCache.wrap(makeTreeCache(), serializer);
ModeledCacheListener<Person> listener = event -> {
    switch ( event.getType() ) {
        case ModeledCacheEventType.NODE_ADDED:
            Person person = event.getNode().getModel();
            handleNewPerson(person);
            break;
        ...
    }
};
cache.getListenable().addListener(listener);