org.elasticsearch.watcher.AbstractResourceWatcher Maven / Gradle / Ivy
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* Licensed to Elasticsearch 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.io.IOException;
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 implements ResourceWatcher {
private final List listeners = new CopyOnWriteArrayList<>();
private boolean initialized = false;
@Override
public void init() throws IOException {
if (!initialized) {
doInit();
initialized = true;
}
}
@Override
public void checkAndNotify() throws IOException {
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 listeners() {
return listeners;
}
/**
* Will be called once on initialization
*/
protected abstract void doInit() throws IOException;
/**
* Will be called periodically
*
* Implementing watcher should check resource and notify all {@link #listeners()}.
*/
protected abstract void doCheckAndNotify() throws IOException;
}