LazyHistoryDescr.java

/*
 * The MIT License
 *
 * Copyright 2013 Mirko Friedenhagen.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package hudson.plugins.jobConfigHistory;

import java.io.IOException;

import com.thoughtworks.xstream.mapper.CannotResolveClassException;

import hudson.XmlFile;

/**
 * Lazy loader for HistoryDescr as preparation for paging.
 *
 * @author Mirko Friedenhagen
 */
public class LazyHistoryDescr extends HistoryDescr {

	HistoryDescr historyDescr = HistoryDescr.EMPTY_HISTORY_DESCR;
	private final XmlFile historyDescriptionFile;

	/**
	 *
	 * @param historyDescriptionFile
	 */
	public LazyHistoryDescr(XmlFile historyDescriptionFile) {
		super(null, null, null, null, null, null);
		this.historyDescriptionFile = historyDescriptionFile;
	}

	/**
	 * {@inheritDoc}.
	 */
	@Override
	public String getUser() {
		return loadAndGetHistory().getUser();
	}

	/**
	 * {@inheritDoc}.
	 */
	@Override
	public String getUserID() {
		return loadAndGetHistory().getUserID();
	}

	/**
	 * {@inheritDoc}.
	 */
	@Override
	public String getOperation() {
		return loadAndGetHistory().getOperation();
	}

	/**
	 * {@inheritDoc}.
	 */
	@Override
	public String getCurrentName() {
		return loadAndGetHistory().getCurrentName();
	}

	/**
	 * {@inheritDoc}.
	 */
	@Override
	public String getOldName() {
		return loadAndGetHistory().getOldName();
	}

	/**
	 * {@inheritDoc}.
	 */
	@Override
	public String getTimestamp() {
		return loadAndGetHistory().getTimestamp();
	}

	/**
	 * Loads configurations on first access of any property.
	 * 
	 * @return historyDescr
	 */
	private HistoryDescr loadAndGetHistory() {
		if (historyDescr == HistoryDescr.EMPTY_HISTORY_DESCR) {
			try {
				historyDescr = (HistoryDescr) historyDescriptionFile.read();
			} catch (IOException ex) {
				throw new RuntimeException(
						"Unable to read " + historyDescriptionFile.getFile(),
						ex);
			} catch (CannotResolveClassException ex) {
				throw new RuntimeException(historyDescriptionFile.getFile()
						+ " is not a history description", ex);
			}
		}
		return historyDescr;
	}

}