java.util.UUID类来生成UUID
import java.util.UUID;public class UUIDGenerator {public static void main(String[] args) {//随机生成一个UUID对象UUID uuid = UUID.randomUUID();System.out.println("生成的UUID为：" + uuid.toString());//通过给定的字符串名称和命名空间生成UUID对象UUID uuid2 = UUID.nameUUIDFromBytes("example_name".getBytes());System.out.println("生成的UUID2为：" + uuid2.toString());}}/*优点：Java自带，无需引入额外的库和依赖；简单易用，一行代码就可以生成UUID。缺点：生成的UUID可能会重复，虽然重复的概率较小，但是在高并发的情况下还是有可能发生；无法控制生成的UUID的格式，只能生成标准的UUID*/Apache Commons IO库中的UUIDUtils类
import org.apache.commons.io.UUIDUtils;public class UUIDGenerator {public static void main(String[] args) {//随机生成一个UUID字符串String uuid = UUIDUtils.randomUUID().toString();System.out.println("生成的UUID为：" + uuid);}}/*三方库优缺点优点：可以生成唯一的UUID；很多开源库和框架都提供了UUID生成的支持。缺点：会增加项目的依赖和复杂度；不同的库实现方式不同，可能会影响生成的UUID的格式和唯一性。*/使用Google Guice库中的UUIDGenerator类生成UUID
import com.google.inject.Inject;import com.google.inject.name.Named;import java.util.UUID;public class UUIDGenerator {private final UUID uuid;@Injectpublic UUIDGenerator(@Named("randomUUID") UUID uuid) {this.uuid = uuid;}public UUID getUUID() {return uuid;}public static void main(String[] args) {UUIDGenerator generator = new UUIDGenerator(UUID.randomUUID());System.out.println("生成的UUID为：" + generator.getUUID().toString());}}使用JDK的MessageDigest类和SecureRandom类：可以通过Hash算法和随机数生成UUID
写法一：import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;import java.security.SecureRandom;import java.util.UUID;public class UUIDGenerator {public static void main(String[] args) throws NoSuchAlgorithmException {SecureRandom secureRandom = new SecureRandom();byte[] seed = secureRandom.generateSeed(16);MessageDigest md5 = MessageDigest.getInstance("MD5");md5.update(seed);UUID uuid = UUID.nameUUIDFromBytes(md5.digest());System.out.println("生成的UUID为：" + uuid.toString());}}写法二：import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;import java.util.Random;public class UUIDGenerator {public static String generateUUID() {String result = "";try {MessageDigest md = MessageDigest.getInstance("MD5");byte[] messageDigest = md.digest((System.currentTimeMillis() + new Random().nextInt(99999999) + "").getBytes());StringBuilder sb = new StringBuilder();for (byte b : messageDigest) {sb.append(String.format("%02x", b));}result = sb.toString();} catch (NoSuchAlgorithmException e) {e.printStackTrace();}return result;}}/*优点：可以通过Hash算法和随机数生成唯一的UUID，具有较高的唯一性；实现简单，无需引入额外的库和依赖。缺点：重复的概率比较难以预测，取决于生成的Hash值的分布情况；无法控制生成的UUID的格式，只能生成基于MD5或SHA-1的UUID。*/使用Snowflake算法生成UUID
Snowflake算法是Twitter开源的分布式ID生成算法，可以在多个节点上生成唯一的ID
import com.github.f4b6a3.uuid.UuidCreator;import com.github.f4b6a3.uuid.enums.UuidVariant;import com.github.f4b6a3.uuid.enums.UuidVersion;import com.github.f4b6a3.uuid.impl.TimeBasedUuidCreator;import java.time.Instant;public class UUIDGenerator {public static void main(String[] args) {UuidCreator creator = TimeBasedUuidCreator.withRandomNodeId();Instant now = Instant.now();long timestamp = now.getEpochSecond() * 1000 + now.getNano() / 1000000;String uuid = creator.create(UuidVersion.VERSION_TIME_BASED, timestamp).toString();System.out.println("生成的UUID为：" + uuid);}}/*优点：可以在分布式系统中生成唯一的ID，具有较高的唯一性和可读性；可以控制生成的ID的格式和信息。缺点：实现相对复杂，需要实现一个全局唯一的时钟服务；只适用于分布式系统，不适用于独立的单机系统。*/Snowflake算法第二种:
public class UUIDGenerator {/** 开始时间截 (2017-01-01) */private final long twepoch = 1483200000000L;/** 机器id所占的位数 */private final long workerIdBits = 5L;/** 数据标识id所占的位数 */private final long datacenterIdBits = 5L;/** 支持的最大机器id，结果是31 */private final long maxWorkerId = -1L ^ (-1L << workerIdBits);/** 支持的最大数据标识id，结果是31 */private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);/** 序列在id中占的位数 */private final long sequenceBits = 12L;/** 机器ID向左移12位 */private final long workerIdShift = sequenceBits;/** 数据标识id向左移17位(12+5) */private final long datacenterIdShift = sequenceBits + workerIdBits;/** 时间截向左移22位(5+5+12) */private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;/** 生成序列的掩码，这里为4095 */private final long sequenceMask = -1L ^ (-1L << sequenceBits);/** 工作机器id(0~31) */private long workerId = 0L;/** 数据中心id(0~31) */private long datacenterId = 0L;/** 毫秒内序列(0~4095) */private long sequence = 0L;/** 上次生成ID的时间截 */private long lastTimestamp = -1L;/** * 构造函数 * * @param workerId 工作ID (0~31) * @param datacenterId 数据中心ID (0~31) */public UUIDGenerator(long workerId, long datacenterId) {if (workerId > maxWorkerId || workerId < 0) {throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));}if (datacenterId > maxDatacenterId || datacenterId < 0) {throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));}this.workerId = workerId;this.datacenterId = datacenterId;}/** * 获得下一个ID (该方法是线程安全的) * * @return SnowflakeId */public synchronized long nextId() {long timestamp = timeGen();// 如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过，此时应当抛出异常if (timestamp < lastTimestamp) {throw new RuntimeException(String.format("Clock moved backwards.Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));}// 如果是同一时间生成的，则进行毫秒内序列if (lastTimestamp == timestamp) {sequence = (sequence + 1) & sequenceMask;// 毫秒内序列溢出if (sequence == 0) {// 阻塞到下一个毫秒,获得新的时间戳timestamp = tilNextMillis(lastTimestamp);}}// 时间戳改变，毫秒内序列重置else {sequence = 0L;}// 上次生成ID的时间截lastTimestamp = timestamp;// 移位并通过或运算拼到一起组成64位的IDreturn ((timestamp - twepoch) << timestampLeftShift) //| (datacenterId << datacenterIdShift) //| (workerId << workerIdShift) //| sequence;}/** * 阻塞到下一个毫秒，直到获得新的时间戳 * * @param lastTimestamp 上次生成ID的时间截 * @return 当前时间戳 */protected long tilNextMillis(long lastTimestamp) {long timestamp = timeGen();while (timestamp <= lastTimestamp) {timestamp = timeGen();}return timestamp;}/** * 返回以毫秒为单位的当前时间 * * @return 当前时间(毫秒) */protected long timeGen() {return System.currentTimeMillis();}}将时间戳和随机数作为种子生成UUID
import java.util.UUID;public class UUIDGenerator {public static void main(String[] args) {long time = System.currentTimeMillis();int random = (int) (Math.random() * Integer.MAX_VALUE);UUID uuid = new UUID(time, random);System.out.println("生成的UUID为：" + uuid.toString());}}使用Redis集群的redisson框架提供的RUID类生成UUID
import org.redisson.api.RUID;public class UUIDGenerator {public static void main(String[] args) {RUID ruid = RUID.randomUID();System.out.println("生成的UUID为：" + ruid.toString());}}利用SecureRandom类生成
import java.security.SecureRandom;import java.util.UUID;public class UUIDGenerator {public static String generateUUID() {return UUID.randomUUID().toString();}public static String generateSecureUUID() {SecureRandom random = new SecureRandom();byte[] bytes = new byte[16];random.nextBytes(bytes);return UUID.nameUUIDFromBytes(bytes).toString();}}三方库详细版
- Apache Commons:
引入以下Maven依赖
<dependency><groupId>commons-lang</groupId><artifactId>commons-lang</artifactId><version>2.6</version></dependency>java示例代码：
import org.apache.commons.lang3.StringUtils;import java.util.UUID;public class GenerateUUID {public static void main(String[] args) {UUID uuid = UUID.randomUUID();String uuidStr = StringUtils.remove(uuid.toString(), '-');System.out.println("UUID：" + uuidStr);}}Google Guava：
Google Guava库可以使用它的UUID类来生成UUID。需要引入以下Maven依赖：
<dependency><groupId>com.google.guava</groupId><artifactId>guava</artifactId><version>30.0-jre</version></dependency>java示例:
import com.google.common.base.CharMatcher;import java.util.UUID;public class GenerateUUID {public static void main(String[] args) {UUID uuid = UUID.randomUUID();String uuidStr = CharMatcher.is('-').removeFrom(uuid.toString());System.out.println("UUID：" + uuidStr);}}注意事项
之前提到了 Apache Commons 的 UUIDUtils 工具类，但是这个工具类实际上是用于字符串格式与 UUID 转化的，而不是生成 UUID。
如果你想要使用 Apache Commons 中的工具类来生成 UUID ，可以使用 RandomStringUtils 类中的 randomUUID() 方法。下面是一个简单示例：
import org.apache.commons.lang3.RandomStringUtils;public class GenerateUUID {public static void main(String[] args) {String uuid = RandomStringUtils.randomNumeric(8) + "-" +RandomStringUtils.randomNumeric(4) + "-" +RandomStringUtils.randomNumeric(4) + "-" +RandomStringUtils.randomNumeric(4) + "-" +RandomStringUtils.randomNumeric(12);System.out.println("UUID：" + uuid);}}/*上述代码中，RandomStringUtils的randomNumeric 方法用于生成指定长度的数字字符串，然后通过字符串拼接的方式生成UUID。需要注意的是，这种方式所生成的UUID并不是符合UUID标准规范的。*/