IdGenerator 唯一Id生成器
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public class IdGenerator {
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private final static long beginTs = 1483200000000L;
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private long lastTs = 0L;
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private long processId;
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private int processIdBits = 10;
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private long sequence = 0L;
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private int sequenceBits = 12;
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public IdGenerator() {
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}
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public IdGenerator(long processId) {
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if (processId > ((1 << processIdBits) - 1)) {
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throw new RuntimeException("进程ID超出范围,设置位数" + processIdBits + ",最大" + ((1 << processIdBits) - 1));
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}
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this.processId = processId;
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}
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protected long timeGen() {
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return System.currentTimeMillis();
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}
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public synchronized long nextId() {
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long ts = timeGen();
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// 刚刚生成的时间戳比上次的时间戳还小,出错
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if (ts < lastTs) {
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throw new RuntimeException("时间戳顺序错误");
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}
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// 刚刚生成的时间戳跟上次的时间戳一样,则需要生成一个sequence序列号
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if (ts == lastTs) {
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// sequence循环自增
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sequence = (sequence + 1) & ((1 << sequenceBits) - 1);
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// 如果sequence=0则需要重新生成时间戳
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if (sequence == 0) {
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// 且必须保证时间戳序列往后
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ts = nextTs(lastTs);
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}
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// 如果ts>lastTs,时间戳序列已经不同了,此时可以不必生成sequence了,直接取0
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} else {
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sequence = 0L;
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}
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// 更新lastTs时间戳
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lastTs = ts;
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return ((ts - beginTs) << (processIdBits + sequenceBits)) | (processId << sequenceBits) | sequence;
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}
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public Long nextShortId() {
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Long shortId = System.currentTimeMillis() / 100 % 1000000000;
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if (shortId < 100000000) {
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shortId += 100000000;
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}
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return shortId;
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}
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protected long nextTs(long lastTs) {
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long ts = timeGen();
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while (ts <= lastTs) {
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ts = timeGen();
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}
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return ts;
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}
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}
试一下这个算法的效率:
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public static void main(String[] args) throws Exception {
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// TODO Auto-generated method stub
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IdGenerator ig = new IdGenerator(1023);
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Long start = System.currentTimeMillis();
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Set<Long> set = new HashSet<Long>();
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for (int i = 0; i < 100000; i++) {
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set.add(ig.nextId());
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}
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System.out.println(set.size());
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System.out.println(System.currentTimeMillis() - start);
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}
结果:
set.size(): 100000
time:115