如何在Java中創建第5類UUID？

Question

在蟒蛇，做一個類型5 UUID我們可以簡單做到：

import uuid 
print uuid.uuid5(uuid.NAMESPACE_URL, 'my string') 

翻翻java documentation for java.util.UUID，我看不出如何做到這一點。首先，類型5沒有提及。他們有一個類型3，但簽名是：

nameUUIDFromBytes(byte[] name) 
Static factory to retrieve a type 3 (name based) UUID based on the specified byte array. 

我們怎樣才能在Java中的5類UUID？

Answer 1

您可以按照https://stackoverflow.com/a/28776880/1452094中提出的代碼自己實現它。 然而，這確實需要一些擺弄，因爲j.u.UUID構造函數需要很長時間。

從Java 8開始，標準庫似乎不支持類型5.但第三方庫（如「Apache Commons Id」）具有支持它的UUID實現。

編輯：這裏是一個全功能的實現：

import java.nio.charset.Charset; 
import java.security.MessageDigest; 
import java.security.NoSuchAlgorithmException; 
import java.util.Objects; 
import java.util.UUID; 

public class UUIDType5 { 
    private static final Charset UTF8 = Charset.forName("UTF-8"); 
    public static final UUID NAMESPACE_DNS = UUID.fromString("6ba7b810-9dad-11d1-80b4-00c04fd430c8"); 
    public static final UUID NAMESPACE_URL = UUID.fromString("6ba7b811-9dad-11d1-80b4-00c04fd430c8"); 
    public static final UUID NAMESPACE_OID = UUID.fromString("6ba7b812-9dad-11d1-80b4-00c04fd430c8"); 
    public static final UUID NAMESPACE_X500 = UUID.fromString("6ba7b814-9dad-11d1-80b4-00c04fd430c8"); 

    public static UUID nameUUIDFromNamespaceAndString(UUID namespace, String name) { 
     return nameUUIDFromNamespaceAndBytes(namespace, Objects.requireNonNull(name, "name == null").getBytes(UTF8)); 
    } 

    public static UUID nameUUIDFromNamespaceAndBytes(UUID namespace, byte[] name) { 
     MessageDigest md; 
     try { 
      md = MessageDigest.getInstance("SHA-1"); 
     } catch (NoSuchAlgorithmException nsae) { 
      throw new InternalError("SHA-1 not supported"); 
     } 
     md.update(toBytes(Objects.requireNonNull(namespace, "namespace is null"))); 
     md.update(Objects.requireNonNull(name, "name is null")); 
     byte[] sha1Bytes = md.digest(); 
     sha1Bytes[6] &= 0x0f; /* clear version  */ 
     sha1Bytes[6] |= 0x50; /* set to version 5  */ 
     sha1Bytes[8] &= 0x3f; /* clear variant  */ 
     sha1Bytes[8] |= 0x80; /* set to IETF variant */ 
     return fromBytes(sha1Bytes); 
    } 

    private static UUID fromBytes(byte[] data) { 
     // Based on the private UUID(bytes[]) constructor 
     long msb = 0; 
     long lsb = 0; 
     assert data.length >= 16; 
     for (int i = 0; i < 8; i++) 
      msb = (msb << 8) | (data[i] & 0xff); 
     for (int i = 8; i < 16; i++) 
      lsb = (lsb << 8) | (data[i] & 0xff); 
     return new UUID(msb, lsb); 
    } 

    private static byte[] toBytes(UUID uuid) { 
     // inverted logic of fromBytes() 
     byte[] out = new byte[16]; 
     long msb = uuid.getMostSignificantBits(); 
     long lsb = uuid.getLeastSignificantBits(); 
     for (int i = 0; i < 8; i++) 
      out[i] = (byte) ((msb >> ((7 - i) * 8)) & 0xff); 
     for (int i = 8; i < 16; i++) 
      out[i] = (byte) ((lsb >> ((15 - i) * 8)) & 0xff); 
     return out; 
    } 
} 

爲了驗證它的工作原理我跑到下面的代碼：

public static void main(String[] args) { 
    UUID test = UUIDType5.nameUUIDFromNamespaceAndString(NAMESPACE_URL, "google.com"); 
    System.out.println(test); 
    System.out.println(test.version()); 
} 

此創建的輸出：

fedb2fa3- 8f5c-5189-80e6-f563dd1cb8f9

驗證對官方Python實現：

>>>打印（uuid.uuid5（uuid.NAMESPACE_URL， 'google.com'））

fedb2fa3-8f5c-5189 -80e6-f563dd1cb8f9