zookeeper Java api - curator 5.6.0

# Pub-Sub Example <!-- Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. --> This example models a publish and subscribe system (note: it is not meant for production) using the strongly typed modeled APIs in Apache Curator. ## Design Notes In this example, there are three models that can be published: `Instance`, `LocationAvailable` and `UserCreated`. Instances have an `InstanceType`; LocationAvailable and UserCreated both have a `Priority` and are associated with a `Group`. (Note: these names/objects are meant for illustrative purposes only and are completely contrived) Each model is stored at a unique path in ZooKeeper: * Instance: `/root/pubsub/instances/TYPE/ID` * LocationAvailable: `/root/pubsub/messages/locations/GROUP/PRIORITY/ID` * UserCreated: `/root/pubsub/messages/users/GROUP/PRIORITY/ID` All models are stored using a TTL so that they automatically get deleted after 10 minutes. ## Clients This example uses the "typed" models (`TypedModelSpec`, etc.). The typed paths, models and clients are meant to be created early in your application and re-used as needed. Thus, you can model your ZooKeeper usage and the rest of your application can use them without worrying about correct paths, types, etc. `TypedModeledFramework` is a template that produces a `ModeledFramework` by applying parameters to the `TypedZPath` in the contained `TypedModelSpec`. Curator provides variants that accept from 1 to 10 parameters (`TypedModeledFramework`, `TypedModeledFramework2`, `TypedModeledFramework3`, etc.). In this example, the TypedModeledFrameworks are defined in `Clients.java`. E.g. ``` public static final TypedModeledFramework2<LocationAvailable, Group, Priority> locationAvailableClient = TypedModeledFramework2.from( ModeledFramework.builder(), builder(LocationAvailable.class), "/root/pubsub/messages/locations/{group}/{priority}" ); ``` ## Publisher `Publisher.java` shows how to use the ModeledFramework to write models. There are methods to write single instances and to write lists of instances in a transaction. Each publish method resolves the appropriate typed client and then calls its `set()` method with the given model. ## Subscriber `Subscriber.java` uses CachedModeledFrameworks to listen for changes on the parent nodes for all of the models in this example. Each of the methods resolves the appropriate typed client and then starts the cache (via `cached()`). ## SubPubTest `SubPubTest.java` is a class that exercises this example. * `start()` uses `Subscriber` to start a `CachedModeledFramework` for each combination of the Instance + InstanceType, LocationAvailable + Group + Priority, and UserCreated + Group + Priority. It then adds a simple listener to each cache that merely prints the class name and path whenever an update occurs (see `generalListener()`). * `start()` also starts a scheduled task that runs every second. This task calls `publishSomething()` * `publishSomething()` randomly publishes either a single Instance, LocationAvailable, UserCreated or a list of those. `SubPubTest.java` has a `main()` method. When you run you should see something similar to this: ``` Publishing 9 instances Subscribed Instance @ /root/pubsub/instances/proxy/1 Subscribed Instance @ /root/pubsub/instances/web/2 Subscribed Instance @ /root/pubsub/instances/cache/4 Subscribed Instance @ /root/pubsub/instances/proxy/9 Subscribed Instance @ /root/pubsub/instances/database/3 Subscribed Instance @ /root/pubsub/instances/cache/5 Subscribed Instance @ /root/pubsub/instances/database/6 Subscribed Instance @ /root/pubsub/instances/cache/7 Subscribed Instance @ /root/pubsub/instances/cache/8 Publishing 1 userCreated Subscribed UserCreated @ /root/pubsub/messages/users/main/high/10 Publishing 9 locationsAvailable Subscribed LocationAvailable @ /root/pubsub/messages/locations/admin/low/11 Subscribed LocationAvailable @ /root/pubsub/messages/locations/admin/medium/12 Subscribed LocationAvailable @ /root/pubsub/messages/locations/admin/medium/13 Subscribed LocationAvailable @ /root/pubsub/messages/locations/admin/medium/14 Subscribed LocationAvailable @ /root/pubsub/messages/locations/admin/medium/16 Subscribed LocationAvailable @ /root/pubsub/messages/locations/admin/high/15 Subscribed LocationAvailable @ /root/pubsub/messages/locations/admin/medium/17 ... ``` It runs for 1 minute and then exits.