Unsigned long and StringConvert. Reference: http://stackoverflow.com/questions/5723579/java-parse-and-unsigned-hex-string-into-a-signed-long http://stackoverflow.com/questions/7031198/java-signed-long-to-unsigned-long-string

LongStringConvertTest.java

import org.junit.Test;

import java.math.BigInteger;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.fail;

/**
 * @author ding.lid
 */
public class LongStringConvertTest {
    @Test
    public void test_long() throws Exception {
        String input = "7bdf55c4112011e3";

        Long result = Long.valueOf(input, 16);
        System.out.println(result);

        String output = Long.toHexString(result);
        System.out.println(output);

        assertEquals(input, output);
    }

    @Test
    public void test_long_overflow() throws Exception {
        String input = "8bdf55c4112011e3";

        try {
            Long.valueOf(input, 16);
            fail();
        } catch (NumberFormatException expected) {
            expected.printStackTrace();
        }
    }

    @Test
    public void test_unsignedLong() throws Exception {
        String input = "8bdf55c4112011e3";

        long value = toSignedLong(input);
        System.out.println(value);

        String output = toUnsignedLongString(value, 16);
        System.out.println(output);

        assertEquals(input, output);
    }

    @Test
    public void test_unsignedLong_Overflow() throws Exception {
        String input = "ffffffffffffffff";
        assertEquals(input, toUnsignedLongString(toSignedLong(input), 16));


        try {
            toSignedLong("10000000000000000");
        } catch (IllegalStateException expected) {
            expected.printStackTrace();
        }
    }

    private static final BigInteger TWO_64 = BigInteger.ONE.shiftLeft(64);

    private static String toUnsignedLongString(long l, int radix) {
        BigInteger b = BigInteger.valueOf(l);
        if (b.signum() < 0) {
            b = b.add(TWO_64);
        }
        return b.toString(radix);
    }

    private static long toSignedLong(String hex) {
        BigInteger big = new BigInteger(hex, 16);
        if (big.compareTo(TWO_64) >= 0) {
            throw new IllegalStateException("Big than 2 ^ 63 - 1: " + hex);
        }
        return big.longValue();
    }
}