Java – Using a UUID as a Database Primary Key, Java type is a byte[]

Are there any issues with using a byte[] as a primary key in a JPA Entity?

I want to use a UUID as my primary key, but stored as a string I feel it will be too large.

I was thinking of doing something like this to store the ID as a byte[] and set it as my Entity's ID:

    public static byte[] byteArray(UUID uuid) {
        long lsb = uuid.getLeastSignificantBits();
        long msb = uuid.getMostSignificantBits();

        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        DataOutputStream dos = new DataOutputStream(bos);
        try {
            dos.writeLong(lsb);
            dos.writeLong(msb);
            dos.flush();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        byte[] data = bos.toByteArray();
//      System.out.println("Byte Array Length "+data.length);
        return data;

    }

Will I have any trouble putting indexes on this in the DB? I am using both Postgres and HSQL. I am using Hibernate as my JPA provider.