/*
* 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
*
* http://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);
}
}