spring AlternativeJdkIdGenerator 源码
spring AlternativeJdkIdGenerator 代码
文件路径：/spring-core/src/main/java/org/springframework/util/AlternativeJdkIdGenerator.java
/*
* Copyright 2002-2015 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.util;
import java.math.BigInteger;
import java.security.SecureRandom;
import java.util.Random;
import java.util.UUID;
/**
* An {@link IdGenerator} that uses {@link SecureRandom} for the initial seed and
* {@link Random} thereafter, instead of calling {@link UUID#randomUUID()} every
* time as {@link org.springframework.util.JdkIdGenerator JdkIdGenerator} does.
* This provides a better balance between securely random ids and performance.
*
* @author Rossen Stoyanchev
* @author Rob Winch
* @since 4.0
*/
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);
}
}
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