How to Generate a UUID in Java

Basic Usage of java.util.UUID

Java has provided the built-in java.util.UUID class since version 1.5, requiring no additional dependencies. UUID.randomUUID() generates UUID v4 (random) and is the most commonly used method. The UUID class also provides methods for parsing, comparing, and formatting UUIDs. UUID objects are immutable and thread-safe, safe to use in concurrent environments.

import java.util.UUID;

public class UUIDExample {
    public static void main(String[] args) {
        // 生成 UUID v4
        UUID uuid = UUID.randomUUID();
        System.out.println(uuid);                    // 标准格式
        System.out.println(uuid.toString());          // 同上
        System.out.println(uuid.toString().toUpperCase()); // 大写
        System.out.println(uuid.toString().replace("-", "")); // 无连字符

        // 获取 UUID 字段
        System.out.println(uuid.version());    // 4
        System.out.println(uuid.variant());    // 2 (IETF)
        System.out.println(uuid.getMostSignificantBits());
        System.out.println(uuid.getLeastSignificantBits());

        // 解析 UUID 字符串
        UUID parsed = UUID.fromString("550e8400-e29b-41d4-a716-446655440000");
        System.out.println(parsed.version()); // 4

        // 从字节数组创建
        byte[] bytes = new byte[16]; // 需要填充
        UUID fromBytes = new UUID(
            java.nio.ByteBuffer.wrap(bytes, 0, 8).getLong(),
            java.nio.ByteBuffer.wrap(bytes, 8, 8).getLong()
        );
    }
}

Using UUID Primary Keys in Spring Boot

// Spring Boot + JPA 实体示例
import jakarta.persistence.*;
import java.util.UUID;

@Entity
@Table(name = "orders")
public class Order {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(columnDefinition = "uuid", updatable = false)
    private UUID id;

    // 或者手动指定生成方式
    @Id
    @Column(nullable = false, updatable = false)
    private UUID id = UUID.randomUUID();

    private String customerName;
    private double amount;

    // 使用 @GenericGenerator (Hibernate)
    // @GeneratedValue(generator = "uuid2")
    // @GenericGenerator(name = "uuid2", strategy = "uuid2")
    // private String id;
}

UUID as REST API Path Parameter

// Spring MVC Controller 示例
import org.springframework.web.bind.annotation.*;
import java.util.UUID;

@RestController
@RequestMapping("/api/users")
public class UserController {

    @GetMapping("/{id}")
    public ResponseEntity getUser(@PathVariable UUID id) {
        // Spring 自动将路径参数字符串转换为 UUID 对象
        // 如果格式不合法，自动返回 400 Bad Request
        return userService.findById(id)
            .map(ResponseEntity::ok)
            .orElse(ResponseEntity.notFound().build());
    }

    @PostMapping
    public ResponseEntity createUser(@RequestBody CreateUserRequest request) {
        UUID newId = UUID.randomUUID();
        User user = userService.create(newId, request);
        URI location = URI.create("/api/users/" + newId);
        return ResponseEntity.created(location).body(user);
    }
}

UUID String Validation

import java.util.UUID;
import java.util.regex.Pattern;

public class UUIDValidator {

    private static final Pattern UUID_PATTERN = Pattern.compile(
        "^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-7][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}$"
    );

    // 方法1：使用正则表达式（严格格式检查）
    public static boolean isValidUUID(String str) {
        return str != null && UUID_PATTERN.matcher(str).matches();
    }

    // 方法2：使用 UUID.fromString（会接受一些非标准格式）
    public static boolean isValidUUIDLoose(String str) {
        try {
            UUID.fromString(str);
            return true;
        } catch (IllegalArgumentException e) {
            return false;
        }
    }
}

Efficient Batch UUID Generation

import java.util.UUID;
import java.util.List;
import java.util.ArrayList;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class BatchUUIDGenerator {

    // 生成指定数量的 UUID 列表
    public static List generate(int count) {
        return IntStream.range(0, count)
            .mapToObj(i -> UUID.randomUUID().toString())
            .collect(Collectors.toList());
    }

    // 生成无连字符格式
    public static List generateCompact(int count) {
        return IntStream.range(0, count)
            .mapToObj(i -> UUID.randomUUID().toString().replace("-", ""))
            .collect(Collectors.toList());
    }

    public static void main(String[] args) {
        List uuids = generate(1000);
        System.out.println("Generated: " + uuids.size() + " UUIDs");
        System.out.println("First: " + uuids.get(0));
    }
}

Using UUID in Kotlin

// Kotlin 示例（使用 Java UUID 类）
import java.util.UUID

// 基本用法
val id: UUID = UUID.randomUUID()
val idStr: String = id.toString()

// 扩展函数让代码更简洁
fun String.toUUID(): UUID = UUID.fromString(this)
fun String.toUUIDOrNull(): UUID? = try { UUID.fromString(this) } catch (e: IllegalArgumentException) { null }

// 使用
val uuid = "550e8400-e29b-41d4-a716-446655440000".toUUID()
val maybeUuid = "invalid".toUUIDOrNull() // null

// data class 中使用
data class Product(
    val id: UUID = UUID.randomUUID(),
    val name: String,
    val price: Double
)