/
AbstractResourceWatcher.java
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/
AbstractResourceWatcher.java
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/*
* Licensed to ElasticSearch and Shay Banon under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. ElasticSearch 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.
*/
package org.elasticsearch.watcher;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
/**
* Abstract resource watcher framework, which handles adding and removing listeners
* and calling resource observer.
*/
public abstract class AbstractResourceWatcher<Listener> implements ResourceWatcher {
private final List<Listener> listeners = new CopyOnWriteArrayList<Listener>();
private boolean initialized = false;
@Override
public void init() {
if (!initialized) {
doInit();
initialized = true;
}
}
@Override
public void checkAndNotify() {
init();
doCheckAndNotify();
}
/**
* Registers new listener
*/
public void addListener(Listener listener) {
listeners.add(listener);
}
/**
* Unregisters a listener
*/
public void remove(Listener listener) {
listeners.remove(listener);
}
/**
* Returns a list of listeners
*/
protected List<Listener> listeners() {
return listeners;
}
/**
* Will be called once on initialization
*/
protected abstract void doInit();
/**
* Will be called periodically
* <p/>
* Implementing watcher should check resource and notify all {@link #listeners()}.
*/
protected abstract void doCheckAndNotify();
}