存储UUID为base64字符串

StackOverflow https://stackoverflow.com/questions/772802

题

我一直在尝试使用UUID作为数据库密钥。我想占用字节尽可能最少量的，同时仍保持UUID表示人类可读的。

我认为，我已经得到它下降到使用Base64和除去一些尾随“==”，似乎是不必要的存储我的目的22个字节。是否有使用这种方法的任何缺陷？

基本上我的测试代码并一串转换来获得UUID下降到22字节字符串，然后将其转换回一个UUID。

import java.io.IOException;
import java.util.UUID;

public class UUIDTest {

    public static void main(String[] args){
        UUID uuid = UUID.randomUUID();
        System.out.println("UUID String: " + uuid.toString());
        System.out.println("Number of Bytes: " + uuid.toString().getBytes().length);
        System.out.println();

        byte[] uuidArr = asByteArray(uuid);
        System.out.print("UUID Byte Array: ");
        for(byte b: uuidArr){
            System.out.print(b +" ");
        }
        System.out.println();
        System.out.println("Number of Bytes: " + uuidArr.length);
        System.out.println();


        try {
            // Convert a byte array to base64 string
            String s = new sun.misc.BASE64Encoder().encode(uuidArr);
            System.out.println("UUID Base64 String: " +s);
            System.out.println("Number of Bytes: " + s.getBytes().length);
            System.out.println();


            String trimmed = s.split("=")[0];
            System.out.println("UUID Base64 String Trimmed: " +trimmed);
            System.out.println("Number of Bytes: " + trimmed.getBytes().length);
            System.out.println();

            // Convert base64 string to a byte array
            byte[] backArr = new sun.misc.BASE64Decoder().decodeBuffer(trimmed);
            System.out.print("Back to UUID Byte Array: ");
            for(byte b: backArr){
                System.out.print(b +" ");
            }
            System.out.println();
            System.out.println("Number of Bytes: " + backArr.length);

            byte[] fixedArr = new byte[16];
            for(int i= 0; i<16; i++){
                fixedArr[i] = backArr[i];
            }
            System.out.println();
            System.out.print("Fixed UUID Byte Array: ");
            for(byte b: fixedArr){
                System.out.print(b +" ");
            }
            System.out.println();
            System.out.println("Number of Bytes: " + fixedArr.length);

            System.out.println();
            UUID newUUID = toUUID(fixedArr);
            System.out.println("UUID String: " + newUUID.toString());
            System.out.println("Number of Bytes: " + newUUID.toString().getBytes().length);
            System.out.println();

            System.out.println("Equal to Start UUID? "+newUUID.equals(uuid));
            if(!newUUID.equals(uuid)){
                System.exit(0);
            }


        } catch (IOException e) {
        }

    }


    public static byte[] asByteArray(UUID uuid) {

        long msb = uuid.getMostSignificantBits();
        long lsb = uuid.getLeastSignificantBits();
        byte[] buffer = new byte[16];

        for (int i = 0; i < 8; i++) {
            buffer[i] = (byte) (msb >>> 8 * (7 - i));
        }
        for (int i = 8; i < 16; i++) {
            buffer[i] = (byte) (lsb >>> 8 * (7 - i));
        }

        return buffer;

    }

    public static UUID toUUID(byte[] byteArray) {

        long msb = 0;
        long lsb = 0;
        for (int i = 0; i < 8; i++)
            msb = (msb << 8) | (byteArray[i] & 0xff);
        for (int i = 8; i < 16; i++)
            lsb = (lsb << 8) | (byteArray[i] & 0xff);
        UUID result = new UUID(msb, lsb);

        return result;
    }

}

输出：

UUID String: cdaed56d-8712-414d-b346-01905d0026fe
Number of Bytes: 36

UUID Byte Array: -51 -82 -43 109 -121 18 65 77 -77 70 1 -112 93 0 38 -2 
Number of Bytes: 16

UUID Base64 String: za7VbYcSQU2zRgGQXQAm/g==
Number of Bytes: 24

UUID Base64 String Trimmed: za7VbYcSQU2zRgGQXQAm/g
Number of Bytes: 22

Back to UUID Byte Array: -51 -82 -43 109 -121 18 65 77 -77 70 1 -112 93 0 38 -2 0 38 
Number of Bytes: 18

Fixed UUID Byte Array: -51 -82 -43 109 -121 18 65 77 -77 70 1 -112 93 0 38 -2 
Number of Bytes: 16

UUID String: cdaed56d-8712-414d-b346-01905d0026fe
Number of Bytes: 36

Equal to Start UUID? true
有帮助吗？

解决方案

您可以安全的将在该应用中填充“==”。如果你是基64文本解码回字节，大多数图书馆希望它在那里，但因为你只是使用生成的字符串作为重点，这不是一个问题。

我喜欢的Base-64，因为它的有限字符集看起来不像乱码，但也有碱基85个。它使用更多的字符和代码4个字节为5个字符，所以你可以让你的文字到20个字符。

其他提示

我也试图做同样的事情。我与它采用的形式6fcb514b-b878-4c9d-95b7-8dc3a7ce6fd8（这是在Java标准的UUID LIB生成）的UUID的Java应用程序的工作。在我来说，我需要的是能够降低得到这个UUID到30个字符或更少。我用的Base64，这些都是我的便利功能。希望他们将是有用的人作为解决方案并不明显，我的时候了。

<强>用法： 

String uuid_str = "6fcb514b-b878-4c9d-95b7-8dc3a7ce6fd8";
String uuid_as_64 = uuidToBase64(uuid_str);
System.out.println("as base64: "+uuid_as_64);
System.out.println("as uuid: "+uuidFromBase64(uuid_as_64));

<强>输出： 

as base64: b8tRS7h4TJ2Vt43Dp85v2A
as uuid  : 6fcb514b-b878-4c9d-95b7-8dc3a7ce6fd8

<强>功能 

import org.apache.commons.codec.binary.Base64;

private static String uuidToBase64(String str) {
    Base64 base64 = new Base64();
    UUID uuid = UUID.fromString(str);
    ByteBuffer bb = ByteBuffer.wrap(new byte[16]);
    bb.putLong(uuid.getMostSignificantBits());
    bb.putLong(uuid.getLeastSignificantBits());
    return base64.encodeBase64URLSafeString(bb.array());
}
private static String uuidFromBase64(String str) {
    Base64 base64 = new Base64(); 
    byte[] bytes = base64.decodeBase64(str);
    ByteBuffer bb = ByteBuffer.wrap(bytes);
    UUID uuid = new UUID(bb.getLong(), bb.getLong());
    return uuid.toString();
}

我在那里我做的几乎一模一样这样的应用程序。 22炭编码UUID。它工作正常。但是，这样一来我做的主要原因是，ID在Web应用程序的URI的暴露，以及36个字符是出现在一个URI的东西真的蛮大的。 22个字符还是有点长，但大家凑合。

下面是这种情况的Ruby代码：

  # Make an array of 64 URL-safe characters
  CHARS64 = ("a".."z").to_a + ("A".."Z").to_a + ("0".."9").to_a + ["-", "_"]
  # Return a 22 byte URL-safe string, encoded six bits at a time using 64 characters
  def to_s22
    integer = self.to_i # UUID as a raw integer
    rval = ""
    22.times do
      c = (integer & 0x3F)
      rval += CHARS64[c]
      integer = integer >> 6
    end
    return rval.reverse
  end

由于使用的base64，将有，如果他们出现在一个URI路径组件进行转义字符它不完全一样的base64编码。 Java的实现可能是完全不同的，因为你很可能有原始字节，而不是一个真正的大整数数组。

下面是我的代码，它使用org.apache.commons.codec.binary.Base64产生网址安全唯一的字符串，其长度为22个字符（和具有的独特性为UUID相同）。

private static Base64 BASE64 = new Base64(true);
public static String generateKey(){
    UUID uuid = UUID.randomUUID();
    byte[] uuidArray = KeyGenerator.toByteArray(uuid);
    byte[] encodedArray = BASE64.encode(uuidArray);
    String returnValue = new String(encodedArray);
    returnValue = StringUtils.removeEnd(returnValue, "\r\n");
    return returnValue;
}
public static UUID convertKey(String key){
    UUID returnValue = null;
    if(StringUtils.isNotBlank(key)){
        // Convert base64 string to a byte array
        byte[] decodedArray = BASE64.decode(key);
        returnValue = KeyGenerator.fromByteArray(decodedArray);
    }
    return returnValue;
}
private static byte[] toByteArray(UUID uuid) {
    byte[] byteArray = new byte[(Long.SIZE / Byte.SIZE) * 2];
    ByteBuffer buffer = ByteBuffer.wrap(byteArray);
    LongBuffer longBuffer = buffer.asLongBuffer();
    longBuffer.put(new long[] { uuid.getMostSignificantBits(), uuid.getLeastSignificantBits() });
    return byteArray;
}
private static UUID fromByteArray(byte[] bytes) {
    ByteBuffer buffer = ByteBuffer.wrap(bytes);
    LongBuffer longBuffer = buffer.asLongBuffer();
    return new UUID(longBuffer.get(0), longBuffer.get(1));
}

你不说你正在使用的数据库管理系统，但似乎RAW将是最好的方法，如果你关心节省空间。你只需要记住所有查询转换，否则你会冒一个巨大的性能下降。

但我要问：是真的字节昂贵你住的地方

下面是与JDK8引入java.util.Base64的示例：

import java.nio.ByteBuffer;
import java.util.Base64;
import java.util.Base64.Encoder;
import java.util.UUID;

public class Uuid64 {

  private static final Encoder BASE64_URL_ENCODER = Base64.getUrlEncoder().withoutPadding();

  public static void main(String[] args) {
    // String uuidStr = UUID.randomUUID().toString();
    String uuidStr = "eb55c9cc-1fc1-43da-9adb-d9c66bb259ad";
    String uuid64 = uuidHexToUuid64(uuidStr);
    System.out.println(uuid64); //=> 61XJzB_BQ9qa29nGa7JZrQ
    System.out.println(uuid64.length()); //=> 22
    String uuidHex = uuid64ToUuidHex(uuid64);
    System.out.println(uuidHex); //=> eb55c9cc-1fc1-43da-9adb-d9c66bb259ad
  }

  public static String uuidHexToUuid64(String uuidStr) {
    UUID uuid = UUID.fromString(uuidStr);
    byte[] bytes = uuidToBytes(uuid);
    return BASE64_URL_ENCODER.encodeToString(bytes);
  }

  public static String uuid64ToUuidHex(String uuid64) {
    byte[] decoded = Base64.getUrlDecoder().decode(uuid64);
    UUID uuid = uuidFromBytes(decoded);
    return uuid.toString();
  }

  public static byte[] uuidToBytes(UUID uuid) {
    ByteBuffer bb = ByteBuffer.wrap(new byte[16]);
    bb.putLong(uuid.getMostSignificantBits());
    bb.putLong(uuid.getLeastSignificantBits());
    return bb.array();
  }

  public static UUID uuidFromBytes(byte[] decoded) {
    ByteBuffer bb = ByteBuffer.wrap(decoded);
    long mostSigBits = bb.getLong();
    long leastSigBits = bb.getLong();
    return new UUID(mostSigBits, leastSigBits);
  }
}

在Base64编码UUID是URL安全，无填充。

下面是我用的UUID（梳状样式）。它包括一个UUID字符串或UUID类型转换为BASE64编码。我这样做，每64位，所以不与任何等号处理：

JAVA 

import java.util.Calendar;
import java.util.UUID;
import org.apache.commons.codec.binary.Base64;

public class UUIDUtil{
    public static UUID combUUID(){
        private UUID srcUUID = UUID.randomUUID();
        private java.sql.Timestamp ts = new java.sql.Timestamp(Calendar.getInstance().getTime().getTime());

        long upper16OfLowerUUID = this.zeroLower48BitsOfLong( srcUUID.getLeastSignificantBits() );
        long lower48Time = UUIDUtil.zeroUpper16BitsOfLong( ts );
        long lowerLongForNewUUID = upper16OfLowerUUID | lower48Time;
        return new UUID( srcUUID.getMostSignificantBits(), lowerLongForNewUUID );
    }   
    public static base64URLSafeOfUUIDObject( UUID uuid ){
        byte[] bytes = ByteBuffer.allocate(16).putLong(0, uuid.getLeastSignificantBits()).putLong(8, uuid.getMostSignificantBits()).array();
        return Base64.encodeBase64URLSafeString( bytes );
    }
    public static base64URLSafeOfUUIDString( String uuidString ){
    UUID uuid = UUID.fromString( uuidString );
        return UUIDUtil.base64URLSafeOfUUIDObject( uuid );
    }
    private static long zeroLower48BitsOfLong( long longVar ){
        long upper16BitMask =  -281474976710656L;
        return longVar & upper16BitMask;
    }
    private static void zeroUpper16BitsOfLong( long longVar ){
        long lower48BitMask =  281474976710656L-1L;
        return longVar & lower48BitMask;
    }
}
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