Java UUID 五个版本的区别及使用场景小结

import java.util.UUID;

public class UUIDVersion1Example {
    public static void main(String[] args) {
        // 生成一个版本1的UUID
        UUID uuid = UUID.nameUUIDFromBytes(("example").getBytes());
        System.out.println("Generated Version 1 UUID: " + uuid);
    }
}

import java.util.UUID;

public class UUIDVersion2Example {
    public static void main(String[] args) {
        // 生成一个版本2的UUID（Java标准库不直接支持，需要自定义实现）
        UUID uuid = UUID.fromString("1e4d5a6b-cdef-2abc-def0-1234567890ab");
        System.out.println("Generated Version 2 UUID: " + uuid);
    }
}

import java.util.UUID;

public class UUIDVersion3Example {
    public static void main(String[] args) {
        // 生成一个版本3的UUID
        UUID namespaceUUID = UUID.fromString("12345678-1234-1234-1234-123456789012");
        String name = "example";
        UUID uuid = UUID.nameUUIDFromBytes((namespaceUUID.toString() + name).getBytes());
        System.out.println("Generated Version 3 UUID: " + uuid);
    }
}

import java.util.UUID;

public class UUIDVersion4Example {
    public static void main(String[] args) {
        // 生成一个版本4的UUID
        UUID uuid = UUID.randomUUID();
        System.out.println("Generated Version 4 UUID: " + uuid);
    }
}

import java.math.BigInteger;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.UUID;

public class UUIDVersion5Example {
    public static void main(String[] args) {
        // 生成一个版本5的UUID
        UUID namespaceUUID = UUID.fromString("12345678-1234-1234-1234-123456789012");
        String name = "example";
        try {
            MessageDigest md = MessageDigest.getInstance("SHA-1");
            byte[] hashBytes = md.digest((namespaceUUID.toString() + name).getBytes(StandardCharsets.UTF_8));
            long msb = 0;
            long lsb = 0;
            for (int i = 0; i < 8; i++) {
                msb = (msb << 8) | (hashBytes[i] & 0xFF);
            }
            for (int i = 8; i < 16; i++) {
                lsb = (lsb << 8) | (hashBytes[i] & 0xFF);
            }
            msb &= 0x0FFFFFFFFFFFFFFFL;
            msb |= 0x5000000000000000L;
            lsb &= 0x3FFFFFFFFFFFFFFFL;
            lsb |= 0x8000000000000000L;
            UUID uuid = new UUID(msb, lsb);
            System.out.println("Generated Version 5 UUID: " + uuid);
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
    }
}