1. public class IdGenerator {
2.  
    
3.  
   private final static long beginTs = 1483200000000L;
4.  
    
5.  
   private long lastTs = 0L;
6.  
    
7.  
   private long processId;
8.  
   private int processIdBits = 10;
9.  
    
10.  
    private long sequence = 0L;
11.  
    private int sequenceBits = 12;
12.  
     
13.  
    public IdGenerator() {
14.  
    }
15.  
     
16.  
    public IdGenerator(long processId) {
17.  
    if (processId > ((1 << processIdBits) – 1)) {
18.  
    throw new RuntimeException(“进程ID超出范围，设置位数” + processIdBits + “，最大” + ((1 << processIdBits) – 1));
19.  
    }
20.  
    this.processId = processId;
21.  
    }
22.  
     
23.  
    protected long timeGen() {
24.  
    return System.currentTimeMillis();
25.  
    }
26.  
     
27.  
    public synchronized long nextId() {
28.  
    long ts = timeGen();
29.  
    // 刚刚生成的时间戳比上次的时间戳还小，出错
30.  
    if (ts < lastTs) {
31.  
    throw new RuntimeException(“时间戳顺序错误”);
32.  
    }
33.  
    // 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
34.  
    if (ts == lastTs) {
35.  
    // sequence循环自增
36.  
    sequence = (sequence + 1) & ((1 << sequenceBits) – 1);
37.  
    // 如果sequence=0则需要重新生成时间戳
38.  
    if (sequence == 0) {
39.  
    // 且必须保证时间戳序列往后
40.  
    ts = nextTs(lastTs);
41.  
    }
42.  
    // 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
43.  
    } else {
44.  
    sequence = 0L;
45.  
    }
46.  
    // 更新lastTs时间戳
47.  
    lastTs = ts;
48.  
    return ((ts – beginTs) << (processIdBits + sequenceBits)) | (processId << sequenceBits) | sequence;
49.  
    }
50.  
     
51.  
    public Long nextShortId() {
52.  
    Long shortId = System.currentTimeMillis() / 100 % 1000000000;
53.  
    if (shortId < 100000000) {
54.  
    shortId += 100000000;
55.  
    }
56.  
    return shortId;
57.  
    }
58.  
     
59.  
    protected long nextTs(long lastTs) {
60.  
    long ts = timeGen();
61.  
    while (ts <= lastTs) {
62.  
    ts = timeGen();
63.  
    }
64.  
    return ts;
65.  
    }
66.  
     
67.  
    }

试一下这个算法的效率：

1.  
   public static void main(String[] args) throws Exception {
2.  
   // TODO Auto-generated method stub
3.  
   IdGenerator ig = new IdGenerator(1023);
4.  
   Long start = System.currentTimeMillis();
5.  
   Set<Long> set = new HashSet<Long>();
6.  
   for (int i = 0; i < 100000; i++) {
7.  
   set.add(ig.nextId());
8.  
   }
9.  
   System.out.println(set.size());
10.  
    System.out.println(System.currentTimeMillis() – start);
11.  
    }

结果：

set.size(): 100000
time：115