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'databene commons' is an open source Java library by Volker Bergmann. It provides extensions to the Java core library by utility classes, abstract concepts and concrete implementations.

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/*
 * Copyright (C) 2004-2015 Volker Bergmann ([email protected]).
 * All rights reserved.
 *
 * Licensed 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.databene.commons;

import java.io.Closeable;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.atomic.AtomicLong;

/**
 * Generates consecutive sequence values and persists sequence state in a properties file.
 * Created: 09.11.2013 09:04:51
 * @since 0.5.25
 * @author Volker Bergmann
 */

public class LocalSequenceProvider implements Closeable {
	
	private static Map INSTANCES = new HashMap();
	
	public static LocalSequenceProvider getInstance(String filename) {
		LocalSequenceProvider result = INSTANCES.get(filename);
		if (result == null) {
			result = new LocalSequenceProvider(filename);
			INSTANCES.put(filename, result);
		}
		return result;
	}
	

	private final String fileName;

	private boolean cached;

	private final Map counters;

	// Initialization --------------------------------------------------------------------------------------------------

	private LocalSequenceProvider(String fileName) {
		this(fileName, true);
	}

	private LocalSequenceProvider(String fileName, boolean cached) {
		this.fileName = fileName;
		this.cached = cached;
		this.counters = new HashMap();
		load();
	}

	// Properties ------------------------------------------------------------------------------------------------------

	public boolean isCached() {
		return cached;
	}

	public void setCached(boolean cached) {
		this.cached = cached;
	}
	
	
	// interface -------------------------------------------------------------------------------------------------------

	public long next(String sequenceName) {
		long result = getOrCreateCounter(sequenceName).incrementAndGet();
		if (!cached)
			save();
		return result;
	}

	@Override
	public void close() {
		save();
	}
	
	
	// static methods --------------------------------------------------------------------------------------------------

	public void save() {
		Map values = new HashMap();
		for (Map.Entry entry : counters.entrySet())
			values.put(entry.getKey(), String.valueOf(entry.getValue().get()));
		try {
			IOUtil.writeProperties(values, fileName);
		} catch (IOException e) {
			throw new RuntimeException(e);
		}
	}
	
	
	// private helpers -------------------------------------------------------------------------------------------------

	private void load() {
		if (IOUtil.isURIAvailable(fileName)) {
			try {
				Map values = IOUtil.readProperties(fileName);
				for (Map.Entry entry : values.entrySet())
					counters.put(entry.getKey(), new AtomicLong(Long.parseLong(entry.getValue())));
			} catch (Exception e) {
				throw new ConfigurationError(e);
			}
		}
	}

	private AtomicLong getOrCreateCounter(String name) {
		AtomicLong counter = counters.get(name);
		if (counter == null) {
			counter = new AtomicLong();
			counters.put(name, counter);
		}
		return counter;
	}

}