class MyClass{
    public String generateSecretToken() {
        Random r = new Random();
        return Long.toHexString(r.nextLong());
    }
}

import org.apache.commons.codec.binary.Hex;

class Class {
    String generateSecretToken() {
        SecureRandom secRandom = new SecureRandom();

        byte[] result = new byte[32];
        secRandom.nextBytes(result);
        return Hex.encodeHexString(result);
    }
}