UUID.java

package io.vivarium.util;

import java.io.Serializable;

import com.google.common.io.BaseEncoding;
import com.google.common.primitives.Longs;
import com.googlecode.gwtstreamer.client.Streamable;

/**
 * Guava based UUID implementation for compatibility with GWT. This class can be used as a plug in replacement for the
 * standard java.util.UUID, but it's worth noting that GWT does not support SecureRandom, so this UUID implementation
 * does not provide the same guarantee of entropy. It's much preferable to generate UUIDs from the java.util.UUID and
 * convert into this class before sending to GWT if possible.
 *
 * @author John H. Uckele
 */
public class UUID implements Serializable, Streamable
{
    private static final long serialVersionUID = -3965221404087809719L;
    private static final BaseEncoding ENCODING = BaseEncoding.base16().lowerCase();
    private final long _long1;
    private final long _long2;

    private UUID()
    {
        _long1 = 0;
        _long2 = 0;
    }

    private UUID(long long1, long long2)
    {
        _long1 = long1;
        _long2 = long2;
    }

    public static UUID randomUUID()
    {
        // This is compatible with a real UUID, but it is not cryptographically secure. In an isolated environment, the
        // cycle time of this UUID generator is only 2^64-1, but there are also 2^64-1 different possible cycles, so
        // collisions should remain improbable.
        long long1 = (Rand.getInstance().getRandomLong()
                | 0b00000000_00000000_00000000_00000000_00000000_00000000_01000000_00000000L)
                & 0b11111111_11111111_11111111_11111111_11111111_11111111_01001111_11111111L;
        long long2 = (Rand.getInstance().getRandomLong2()
                | 0b10000000_00000000_00000000_00000000_00000000_00000000_00000000_00000000L)
                & 0b10111111_11111111_11111111_11111111_11111111_11111111_11111111_11111111L;

        return new UUID(long1, long2);
    }

    @Override
    public String toString()
    {
        StringBuilder sb = new StringBuilder();

        // encode first long
        byte[] bytes1 = Longs.toByteArray(_long1);
        sb.append(ENCODING.encode(bytes1, 0, 4)).append('-');
        sb.append(ENCODING.encode(bytes1, 4, 2)).append('-');
        sb.append(ENCODING.encode(bytes1, 6, 2)).append('-');
        // encode second long
        byte[] bytes2 = Longs.toByteArray(_long2);
        sb.append(ENCODING.encode(bytes2, 0, 2)).append('-');
        sb.append(ENCODING.encode(bytes2, 2, 6));

        return sb.toString();
    }

    public static UUID fromString(String s)
    {
        s = s.replaceAll("-", "").toLowerCase();

        // decode first long
        byte[] bytes1 = ENCODING.decode(s.substring(0, 16));
        long long1 = Longs.fromByteArray(bytes1);

        // decode second long
        byte[] bytes2 = ENCODING.decode(s.substring(16, 32));
        long long2 = Longs.fromByteArray(bytes2);

        return new UUID(long1, long2);
    }

    @Override
    public int hashCode()
    {
        return toString().hashCode();
    }

    @Override
    public boolean equals(Object that)
    {
        return this.toString().equals(String.valueOf(that));
    }
}