com.kaka.util.NanoId Maven / Gradle / Ivy
package com.kaka.util;
import java.security.SecureRandom;
import java.util.Random;
/**
* A class for generating unique String IDs.
*
* The implementations of the core logic in this class are based on NanoId, a JavaScript
* library by Andrey Sitnik released under the MIT license. (https://github.com/ai/nanoid)
*
* @author David Klebanoff
*/
public class NanoId {
/**
* NanoIdUtils instances should NOT be constructed in standard programming.
* Instead, the class should be used as NanoIdUtils.randomNanoId();.
*/
private NanoId() {
//Do Nothing
}
/**
* The default random number generator used by this class.
* Creates cryptographically strong NanoId Strings.
*/
public static final SecureRandom DEFAULT_NUMBER_GENERATOR = new SecureRandom();
/**
* The default alphabet used by this class.
* Creates url-friendly NanoId Strings using 64 unique symbols.
*/
public static final char[] DEFAULT_ALPHABET =
"_-0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();
/**
* The default size used by this class.
* Creates NanoId Strings with slightly more unique values than UUID v4.
*/
public static final int DEFAULT_SIZE = 21;
/**
* Static factory to retrieve a url-friendly, pseudo randomly generated, NanoId String.
*
* The generated NanoId String will have 21 symbols.
*
* The NanoId String is generated using a cryptographically strong pseudo random number
* generator.
*
* @return A randomly generated NanoId String.
*/
public static String randomNanoId() {
return randomNanoId(DEFAULT_NUMBER_GENERATOR, DEFAULT_ALPHABET, DEFAULT_SIZE);
}
/**
* Static factory to retrieve a NanoId String.
*
* The string is generated using the given random number generator.
*
* @param random The random number generator.
* @param alphabet The symbols used in the NanoId String.
* @param size The number of symbols in the NanoId String.
* @return A randomly generated NanoId String.
*/
public static String randomNanoId(final Random random, final char[] alphabet, final int size) {
if (random == null) {
throw new IllegalArgumentException("random cannot be null.");
}
if (alphabet == null) {
throw new IllegalArgumentException("alphabet cannot be null.");
}
if (alphabet.length == 0 || alphabet.length >= 256) {
throw new IllegalArgumentException("alphabet must contain between 1 and 255 symbols.");
}
if (size <= 0) {
throw new IllegalArgumentException("size must be greater than zero.");
}
final int mask = (2 << (int) Math.floor(Math.log(alphabet.length - 1) / Math.log(2))) - 1;
final int step = (int) Math.ceil(1.6 * mask * size / alphabet.length);
final StringBuilder idBuilder = new StringBuilder();
while (true) {
final byte[] bytes = new byte[step];
random.nextBytes(bytes);
for (int i = 0; i < step; i++) {
final int alphabetIndex = bytes[i] & mask;
if (alphabetIndex < alphabet.length) {
idBuilder.append(alphabet[alphabetIndex]);
if (idBuilder.length() == size) {
return idBuilder.toString();
}
}
}
}
}
}