JDK之UUID

系统管理员 2022-05-11 02:20 235阅读 0赞

## 运用 ##

### 示例 ###

public static void main(String[] args) { 
        System.out.println("格式前的UUID ： " + UUID.randomUUID().toString());
        System.out.println("格式前的UUID ： " + UUID.randomUUID().toString().length());
        System.out.println("格式化后的UUID ：" + UUID.randomUUID().toString().replace("-", ""));
        System.out.println("格式化后的UUID ：" + UUID.randomUUID().toString().replace("-", "").length());
    }

### 结果 ###

格式前的UUID ： f6429b4c-21b3-43d8-a10f-765ac15e52c1
    格式前的UUID ： 36
    格式化后的UUID ：52ecf5405f4f424cab92254426fe1baa
    格式化后的UUID ：32

## 源码 ##

/** * Static factory to retrieve a type 4 (pseudo randomly generated) UUID. * * The {@code UUID} is generated using a cryptographically strong pseudo * random number generator. * * @return A randomly generated {@code UUID} */
    public static UUID randomUUID() { 
        SecureRandom ng = Holder.numberGenerator;
    
        byte[] randomBytes = new byte[16];
        ng.nextBytes(randomBytes);
        randomBytes[6]  &= 0x0f;  /* clear version */
        randomBytes[6]  |= 0x40;  /* set to version 4 */
        randomBytes[8]  &= 0x3f;  /* clear variant */
        randomBytes[8]  |= 0x80;  /* set to IETF variant */
        return new UUID(randomBytes);
    }
    
    /* * Private constructor which uses a byte array to construct the new UUID. */
    private UUID(byte[] data) { 
        long msb = 0;
        long lsb = 0;
        assert data.length == 16 : "data must be 16 bytes in length";
        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);
        this.mostSigBits = msb;
        this.leastSigBits = lsb;
    }

## Spring Core自定义的UUID生成器 ##

package org.springframework.util;
    
    import java.math.BigInteger;
    import java.security.SecureRandom;
    import java.util.Random;
    import java.util.UUID;
    
    public class AlternativeJdkIdGenerator implements IdGenerator { 
    
    	private final Random random;
    
    
    	public AlternativeJdkIdGenerator() { 
    		SecureRandom secureRandom = new SecureRandom();
    		byte[] seed = new byte[8];
    		secureRandom.nextBytes(seed);
    		this.random = new Random(new BigInteger(seed).longValue());
    	}
    
    
    	@Override
    	public UUID generateId() { 
    		byte[] randomBytes = new byte[16];
    		this.random.nextBytes(randomBytes);
    
    		long mostSigBits = 0;
    		for (int i = 0; i < 8; i++) { 
    			mostSigBits = (mostSigBits << 8) | (randomBytes[i] & 0xff);
    		}
    
    		long leastSigBits = 0;
    		for (int i = 8; i < 16; i++) { 
    			leastSigBits = (leastSigBits << 8) | (randomBytes[i] & 0xff);
    		}
    
    		return new UUID(mostSigBits, leastSigBits);
    	}
    
    }