isbnvalidator.java

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package de.fhm.jkf.bookshop.clsv;

import java.util.StringTokenizer;

/*
 * <br><br><center><table border="1" width="80%"><hr>
 * <strong>
 * <a href="http://jkf.sourceforge.net">The JKF Project</a>
 * </strong>
 * <p>
 * Copyright (C) 2003 by Theodor Willax
 * <p>
 * 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.
 * <p>
 * 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.
 * <p>
 * You should have received a copy of the <a href="http://www.gnu.org/copyleft/lesser.html">
 * GNU Lesser General Public License</a> along with this library; if not, write to
 * the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
 * MA  02111-1307  USA
 * <hr></table></center>
 */

/**
 * Checks if a given ISBN is correct.
 * <br>
 * What is the format of a ISBN?<br>
 * Every ISBN consists of ten digits and whenever
 * it is printed it is preceded by the letters ISBN.
 * The ten-digit number is divided into four parts
 * of variable length, each part separated by a hyphen.
 * See <a href="http://www.isbn.org/standards/home/isbn/us/isbnqa.asp#Q3">
 * www.isbn.org</a> for detailed information about a isbn.
 * <br>
 * The preceding letters "ISBN" will be left an it would be an error
 * if the are contained in the string which should be checked.
 * 
 * @version $$Revision: 1.1 $$
 * @author Theodor Willax
 */
public class IsbnValidator {
	/**
	 * Validates if the given <code>String</code> is a valid ISBN.
	 * 
	 * @return IsbnValidatorResult type
	 * @see de.fhm.jkf.bookshop.clsv.IsbnValidatorResult
	 */
	public IsbnValidatorResult isIsbn(String isbn) {
		if (isbn == null || !this.isLengthOk(isbn)) {
			return IsbnValidatorResult.VALIDATION_ERROR_LENGTH;
		}

		if (!this.isHyphenCountOk(isbn)) {
			return IsbnValidatorResult.VALIDATION_ERROR_HYPHEN_COUNT;
		}

		if (!this.isPartCompositionOk(isbn)) {
			return IsbnValidatorResult.VALIDATION_ERROR_PART_COMPOSITION;
		}
		return IsbnValidatorResult.VALIDATION_SUCCESS;
	}

	/**
	 * Validates if the length of the given ISBN is ok.
	 * It must have 10 digits plus 3 hyphens (= 13).
	 * 
	 * @return true if length is ok, false otherwise.
	 */
	private boolean isLengthOk(String isbn) {
		return isbn.length() == 13;
	}

	/**
	 * ISBN's must have exactly 3 hyphens. Hyphens can not be
	 * side by side, there is always at least one digit between.
	 * 
	 * returns true if number and position of hyphens is ok, false otherwise.
	 */
	private boolean isHyphenCountOk(String isbn) {
		// do we have 3 hyphens
		int idx = 0, idxOld = 0, hyphenCount = 0;
		while ((idxOld = isbn.indexOf('-', idx)) != -1) {
			// 2 hyphens side by side are not allowed
			if (idxOld + 1 == idx) {
				hyphenCount = 0;
				break;
			}
			idx = idxOld + 1;
			hyphenCount++;
		}
		return hyphenCount == 3;
	}

	/**
	 * A ISBN consists of four valid parts, each separated
	 * by a hyphen.
	 * 
	 * @return true if all parts are ok, false otherwise.
	 */
	private boolean isPartCompositionOk(String isbn) {
		boolean parts = false;
		int i = 0;
		StringTokenizer tokenizer = new StringTokenizer(isbn, "-");
		while (tokenizer.hasMoreElements()) {
			i++;
			String token = tokenizer.nextToken();
			if (i != 4) {
				try {
					Integer.parseInt(token);
				} catch (NumberFormatException e) {
					return false;
				}
			} else {
				if (token.length() != 1) {
					return false;
				}
				// the last token can be one digit or 'X'
				if (token.equals("X")) {
					return true;
				}
				try {
					Integer.parseInt(token);
				} catch (NumberFormatException e) {
					return false;
				}
				return true;
			}
		}
		return false;
	}
}