CPF Value Object

CPF.java

import java.util.stream.IntStream;

public class CPF {

	private final String root;
	private final String checksum;
	private final int    regionCode;
	private final Region region;

	public CPF(String baseValue) {
		String numericCharacters = stripNonNumericCharacters(baseValue);
		validateInput(numericCharacters);

		String rootCandidate     = numericCharacters.substring(0, 9);
		String checksumCandidate = numericCharacters.substring(9);
		validateChecksum(rootCandidate, checksumCandidate);

		root       = rootCandidate;
		checksum   = checksumCandidate;
		regionCode = Integer.parseUnsignedInt(String.valueOf(numericCharacters.charAt(8)));
		region     = Region.fromCode(regionCode);
	}

	private String stripNonNumericCharacters(String value) {
		return value.trim().replaceAll("\\D", "");
	}

	private void validateInput(String value) {
		if (value == null || value.isEmpty()) {
			throw new IllegalArgumentException("CPF deve ser informado");
		}
		if (!value.matches("\\d{11}")) {
			throw new IllegalArgumentException("CPF deve conter 11 dígitos numéricos");
		}
		// Se o CPF informado for uma repetição de um mesmo algarismo (ex.: "11111111111"), será considerado inválido
		if (value.equals(String.valueOf(value.charAt(0)).repeat(11))) {
			throw new IllegalArgumentException("CPF inválido");
		}
	}

	private void validateChecksum(String root, String checksum) {
		if (!checksum.equals(getChecksumFor(root))) {
			throw new IllegalArgumentException("CPF inválido");
		}
	}

	private String getChecksumFor(String root) {
		StringBuilder resultChecksum = new StringBuilder();
		StringBuilder tempRoot       = new StringBuilder(root);

		int firstSum = IntStream.range(0, 9)
		                        .map(i -> Character.getNumericValue(tempRoot.toString().charAt(i)) * (i + 1))
		                        .sum();
		int firstDigit = (firstSum % 11) % 10;

		resultChecksum.append(firstDigit);
		tempRoot.append(firstDigit);

		int secondSum = IntStream.range(0, 10)
		                         .map(i -> Character.getNumericValue(tempRoot.toString().charAt(i)) * i)
		                         .sum();
		int secondDigit = (secondSum % 11) % 10;

		resultChecksum.append(secondDigit);

		return resultChecksum.toString();
	}

	@Override
	public String toString() {
		return root.substring(0, 3) + '.'
				+ root.substring(3, 6) + '.'
				+ root.substring(6, 9)
				+ '-' + checksum.substring(0, 2);
	}

}

Region.java

public enum Region {

	RS(0),
	DF_GO_MS_MT_TO(1),
	AC_AM_AP_PA_RO_RR(2),
	CE_MA_PI(3),
	AL_PB_PE_RN(4),
	BA_SE(5),
	MG(6),
	ES_RJ(7),
	SP(8),
	PR_SC(9);

	private final int code;

	Region(int code) {
		this.code = code;
	}

	public static Region fromCode(int code) {
		for (Region region : values()) {
			if (region.code == code) {
				return region;
			}
		}
		return null;
	}
}