rrdmemorybackendfactory.java

jrobin,使用纯java实现的RRD数据库,使用RRD数据库来统计数据.

/* ============================================================
 * JRobin : Pure java implementation of RRDTool's functionality
 * ============================================================
 *
 * Project Info:  http://www.jrobin.org
 * Project Lead:  Sasa Markovic ([e-mail]);
 *
 * (C) Copyright 2003-2005, by Sasa Markovic.
 *
 * Developers:    Sasa Markovic ([e-mail])
 *
 *
 * This library is free software; you can redistribute it and/or modify it under the terms
 * of the GNU Lesser General Public License as published by the Free Software Foundation;
 * either version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License along with this
 * library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
 * Boston, MA 02111-1307, USA.
 */

package org.jrobin.core;

import java.io.IOException;
import java.util.HashMap;

/**
 * Factory class which creates actual {@link RrdMemoryBackend} objects. JRobin's support
 * for in-memory RRDs is still experimental. You should know that all active RrdMemoryBackend
 * objects are held in memory, each backend object stores RRD data in one big byte array. This
 * implementation is therefore quite basic and memory hungry but runs very fast.<p>
 * <p/>
 * Calling {@link RrdDb#close() close()} on RrdDb objects does not release any memory at all
 * (RRD data must be available for the next <code>new RrdDb(path)</code> call. To release allocated
 * memory, you'll have to call {@link #delete(String) delete(path)} method of this class.<p>
 */
public class RrdMemoryBackendFactory extends RrdBackendFactory {
	/**
	 * factory name, "MEMORY"
	 */
	public static final String NAME = "MEMORY";
	private HashMap<String, RrdMemoryBackend> backends = new HashMap<String, RrdMemoryBackend>();

	/**
	 * Creates RrdMemoryBackend object.
	 *
	 * @param id	   Since this backend holds all data in memory, this argument is interpreted
	 *                 as an ID for this memory-based storage.
	 * @param readOnly This parameter is ignored
	 * @return RrdMemoryBackend object which handles all I/O operations
	 * @throws IOException Thrown in case of I/O error.
	 */
	protected synchronized RrdBackend open(String id, boolean readOnly)
			throws IOException {
		RrdMemoryBackend backend;
		if (backends.containsKey(id)) {
			backend = backends.get(id);
		}
		else {
			backend = new RrdMemoryBackend(id);
			backends.put(id, backend);
		}
		return backend;
	}

	/**
	 * Method to determine if a memory storage with the given ID already exists.
	 *
	 * @param id Memory storage ID.
	 * @return True, if such storage exists, false otherwise.
	 */
	protected synchronized boolean exists(String id) {
		return backends.containsKey(id);
	}

	/**
	 * Removes the storage with the given ID from the memory.
	 *
	 * @param id Storage ID
	 * @return True, if the storage with the given ID is deleted, false otherwise.
	 */
	public boolean delete(String id) {
		if (backends.containsKey(id)) {
			backends.remove(id);
			return true;
		}
		else {
			return false;
		}
	}

	/**
	 * Returns the name of this factory.
	 *
	 * @return Factory name (equals to "MEMORY").
	 */
	public String getFactoryName() {
		return NAME;
	}
}