Validator of national identification number used in the Czech Republic.

RCValidator.java

import static java.util.Calendar.DAY_OF_MONTH;
import static java.util.Calendar.MONTH;
import static java.util.Calendar.YEAR;

import java.util.Calendar;

/**
 * 
 * Validator of national identification number used in the Czech Republic.
 * 
 * See wiki <a href="http://cs.wikipedia.org/wiki/Rodn%C3%A9_%C4%8D%C3%ADslo">http://cs.wikipedia.org/wiki/Rodn%C3%A9_%C4%8D%C3%ADslo</a>
 * 
 * @author banterCZ
 */
public class RCValidator {

	/**
	 * Validates the given national identification number. 
	 * 
	 * @param value to validate (without slash, e.g. 7310285169), may be <code>null</code> or an empty string but returns <code>false</code> in that case
	 * @return <code>true</code> when number is valid, <code>false</code> otherwise
	 */
	public boolean isValid(String value) {
		if (value == null) {
			return false;
		}
		
		if (value.length() < 9 || value.length() > 10) {
			return false;
		}
		
		int year;
		int month;
		int day;
		
		try {
			year = Integer.parseInt(value.substring(0, 2));
			month = Integer.parseInt(value.substring(2, 4));
			day = Integer.parseInt(value.substring(4, 6));
		} catch (NumberFormatException e) {
			return false;
		}
		
		if (value.length() == 9 && (year >= 54)) {
			return false;
		}
		
		if (value.length() == 10) {
			long mod = Long.parseLong(value.substring(0, 9)) % 11;
			int lastNumber = Integer.parseInt(value.substring(9));
			if (mod == 10) {
				if (lastNumber != 0) {
					return false;
				}
			} else if (lastNumber != mod) {					
				return false;
			}
		}
		
		return isDayAndMonthValid(value, year, month, day);
	}

	private boolean isDayAndMonthValid(String value, int year, int month, int day) {
		year = getYearWithHunders(year, value);
		month = getRealMonth(year, month);

		if (month == 0 || month > 12) {
			return false;
		}

		if (day == 0) {
			return false;
		}

		Calendar calendar = Calendar.getInstance();
		calendar.clear();
		calendar.set(YEAR, year);
		calendar.set(MONTH, month - 1);
		
		int daysInMonth = calendar.getActualMaximum(DAY_OF_MONTH);
		
		if (daysInMonth < day) {
			return false;
		}
		
		return true;
	}

	/**
	 * Removes possible offset (20, 50, or 70).
	 * 
	 * @param year
	 * @param month may be with offset
	 * @return month without offset
	 */
	private int getRealMonth(int year, int month) {
		if ((month > 70) && (year > 2003)) {
			month -= 70;
		} else if (month > 50) {
			month -= 50;
		} else if ((month > 20) && (year > 2003)) {
			month -= 20;
		}
		return month;
	}

	/**
	 * Possible problem. People born before 1954 usually have the national identification number of length 9 but might be also 10.
	 * Little bit risky for somebody who is hundred-year old.
	 * 
	 * @param year
	 * @param value
	 * @return
	 */
	private int getYearWithHunders(int year, String value) {
		if (value.length() == 9) {
			return year + 1900;
		}
		
		if (year > Calendar.getInstance().get(YEAR) % 100) {
			return year + 1900;
		} else {
			return year + 2000;
		}
		
	}
}

RCValidatorTest.java

import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

import org.junit.Before;
import org.junit.Test;

/**
 * Test for {@link RCValidator}.
 * 
 * @author banterCZ
 */
public class RCValidatorTest {
	
	private RCValidator validator;
	
	@Before
	public void setUp() {
		validator = new RCValidator();
	}

	@Test
	public void nullValue() {
		boolean result = validator.isValid(null);
		assertFalse(result);
	}
	
	@Test
	public void empty() {
		boolean result = validator.isValid("");
		assertFalse(result);
	}
	
	@Test
	public void numberFormatException() {
		boolean result = validator.isValid("x123456789");
		assertFalse(result);
	}
	
	/**
	 * Only 8 instead of 9 or 10 numbers.
	 */
	@Test
	public void invalidLengthShort() {
		boolean result = validator.isValid("73602851");
		assertFalse(result);
	}
	
	/**
	 * Too many characters, 11 instead of 9 or 10 numbers.
	 */
	@Test
	public void invalidLengthLong() {
		boolean result = validator.isValid("73102851691");
		assertFalse(result);
	}
	
	/**
	 * 731028/5169
	 */
	@Test
	public void validNormalMan() {
		boolean result = validator.isValid("7310285169");
		assertTrue(result);
	}
	
	/**
	 * 736000/5158
	 */
	@Test
	public void invalidDayZero() {
		boolean result = validator.isValid("7360005158");
		assertFalse(result);
	}
	
	/**
	 * 736033/5158
	 */
	@Test
	public void invalidDay() {
		boolean result = validator.isValid("7360335158");
		assertFalse(result);
	}
	
	/**
	 * 120230/0011
	 */
	@Test
	public void invalidDayFebruary() {
		boolean result = validator.isValid("1202300011");
		assertFalse(result);
	}
	
	/**
	 * 2011-02-29
	 */
	@Test
	public void invalidLeapYear() {
		boolean result = validator.isValid("1102290002");
		assertFalse(result);
	}
	
	/**
	 * 2012-02-29
	 */
	@Test
	public void validLeapYear() {
		boolean result = validator.isValid("1202290001");
		assertTrue(result);
	}
	
	/**
	 * Only about 1000 existing birthNumbers
	 * 
	 * 840501/1330
	 */
	@Test
	public void validExceptionMod11() {
		boolean result = validator.isValid("8405011330");
		assertTrue(result);
	}
	
	/**
	 * 840501/133
	 * @see #validExceptionMod11()
	 */
	@Test
	public void invalidExceptionMod11() {
		boolean result = validator.isValid("8405011331");
		assertFalse(result);
	}
	
	/**
	 * 835607/8656
	 */
	@Test
	public void invalid() {
		boolean result = validator.isValid("8356078656");
		assertFalse(result);
	}
	
	/**
	 * 530506/1234
	 * May happen, but default length for years 1953 and earlier is 9.
	 */
	@Test
	public void oldValid10() {
		boolean result = validator.isValid("5305061234");
		assertTrue(result);
	}
	
	/**
	 * 530506/123
	 */
	@Test
	public void oldValid9() {
		boolean result = validator.isValid("530506123");
		assertTrue(result);
	}
	
	/**
	 * 530506/12
	 */
	@Test
	public void oldInvalid8() {
		boolean result = validator.isValid("53050612");
		assertFalse(result);
	}
	
	/**
	 * 540506/123
	 */
	@Test
	public void newInvalid8() {
		boolean result = validator.isValid("540506123");
		assertFalse(result);
	}
	
	/**
	 * 120203/1237
	 */
	@Test
	public void validAfter2K() {
		boolean result = validator.isValid("1202031237");
		assertTrue(result);
	}
	
	/**
	 * 128231/0007
	 */
	@Test
	public void monthOffset70() {
		boolean result = validator.isValid("1282310007");
		assertTrue(result);
	}
	
	/**
	 * 038231/0005
	 */
	@Test
	public void invalidMonthOffset70() {
		boolean result = validator.isValid("0382310005");
		assertFalse(result);
	}
	
	/**
	 * 126231/0005
	 */
	@Test
	public void monthOffset50() {
		boolean result = validator.isValid("1262310005");
		assertTrue(result);
	}
	
	/**
	 * 123231/0002
	 */
	@Test
	public void monthOffset20() {
		boolean result = validator.isValid("1232310002");
		assertTrue(result);
	}
	
	/**
	 * 033231/0000
	 */
	@Test
	public void invalidMonthOffset20() {
		boolean result = validator.isValid("0332310000");
		assertFalse(result);
	}
	
	/**
	 * 120001/0009
	 */
	@Test
	public void invalidMonth() {
		boolean result = validator.isValid("1200010009");
		assertFalse(result);
	}
	
}

    /**
     * Invalid (non-numeric) characters: 123456/foo!
     */
    @Test
    public void invalidCharacters() {
        boolean result = validator.isValid("123456foo!");
        assertFalse(result);
    }

    /**
     * Minus sign: -20101/000
     */
    @Test
    public void negativeYear() {
        boolean result = validator.isValid("-20101000");
        assertFalse(result);
    }