org.elasticsearch.watcher.AbstractResourceWatcher Maven / Gradle / Ivy

Go to download
/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the "Elastic License
 * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
 * Public License v 1"; you may not use this file except in compliance with, at
 * your election, the "Elastic License 2.0", the "GNU Affero General Public
 * License v3.0 only", or the "Server Side Public License, v 1".
 */
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 == false) {
            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;

}