BooleanComparator.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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.apache.metamodel.util;

import java.util.Comparator;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Comparator of booleans
 */
public final class BooleanComparator implements Comparator<Object> {

	private static final Logger logger = LoggerFactory
			.getLogger(BooleanComparator.class);

	private static BooleanComparator _instance = new BooleanComparator();

	private BooleanComparator() {
	}

	public static Comparator<Object> getComparator() {
		return _instance;
	}

	public static Comparable<Object> getComparable(Object object) {
		final Boolean b = toBoolean(object);
		return new Comparable<Object>() {

			@Override
			public boolean equals(Object obj) {
				return _instance.equals(obj);
			}

			public int compareTo(Object o) {
				return _instance.compare(b, o);
			}

			@Override
			public String toString() {
				return "BooleanComparable[boolean=" + b + "]";
			}
		};
	}

	public int compare(Object o1, Object o2) {
		if (o1 == null && o2 == null) {
			return 0;
		}
		if (o1 == null) {
			return -1;
		}
		if (o2 == null) {
			return 1;
		}
		Boolean b1 = toBoolean(o1);
		Boolean b2 = toBoolean(o2);
		return b1.compareTo(b2);
	}

	public static Boolean toBoolean(Object o) {
		if (o == null) {
			return null;
		}

		if (o instanceof Boolean) {
			return (Boolean) o;
		}
		if (o instanceof String) {
			try {
				return parseBoolean((String) o);
			} catch (IllegalArgumentException e) {
				logger.warn(
						"Could not convert String '{}' to boolean, returning false", o);
				return false;
			}
		}
		if (o instanceof Number) {
			int i = ((Number) o).intValue();
			return i >= 1;
		}
		
		logger.warn(
				"Could not convert '{}' to boolean, returning false",
				o);
		return false;
	}

	/**
	 * Parses a string and returns a boolean representation of it. To parse the
	 * string the following values will be accepted, irrespective of case.
	 * <ul>
	 * <li>true</li>
	 * <li>false</li>
	 * <li>1</li>
	 * <li>0</li>
	 * <li>yes</li>
	 * <li>no</li>
	 * <li>y</li>
	 * <li>n</li>
	 * </ul>
	 * 
	 * @param string
	 *            the string to parse
	 * @return a boolean
	 * @throws IllegalArgumentException
	 *             if the string provided is null or cannot be parsed as a
	 *             boolean
	 */
	public static boolean parseBoolean(String string)
			throws IllegalArgumentException {
		if (string == null) {
			throw new IllegalArgumentException("string cannot be null");
		}
		string = string.trim();
		if ("true".equalsIgnoreCase(string) || "1".equals(string)
				|| "y".equalsIgnoreCase(string)
				|| "yes".equalsIgnoreCase(string)) {
			return true;
		} else if ("false".equalsIgnoreCase(string) || "0".equals(string)
				|| "n".equalsIgnoreCase(string)
				|| "no".equalsIgnoreCase(string)) {
			return false;
		} else {
			throw new IllegalArgumentException(
					"Could not get boolean value of string: " + string);
		}
	}

	public static boolean isBoolean(Object o) {
		if (o instanceof Boolean) {
			return true;
		}
		if (o instanceof String) {
			if ("true".equalsIgnoreCase((String) o)
					|| "false".equalsIgnoreCase((String) o)) {
				return true;
			}
		}
		return false;
	}

}