对于分布式系统环境，主键id的设计很关键，什么自增intid那些是绝对不用的，比较早的时候，大部分系统都用uuid/guid来作为主键，优点是方便又能解决问题，缺点是插入时因为uuid/guid的不规则导致每插入一条数据就需要重新排列一次，性能低下；也有人提出用uuid/guid转long的方式，可以很明确的告诉你，这种方式long不能保证唯一，大并发下会有重复long出现，所以也不可取，这个主键设计问题曾经是很多公司系统设计的一个头疼点，所以大部分公司愿意牺牲一部分性能而直接采用简单粗暴的uuid/guid来作为分布式系统的主键；
twitter开源了一个snowflake算法，俗称雪花算法；就是为了解决分布式环境下生成不同id的问题；该算法会生成19位的long型有序数字，mysql中用bigint来存储（bigint长度为20位）；该算法应该是目前分布式环境中主键id最好的解决方案之一了；
好，废话不多说，直接上算法实现
我要评论 1 package com.anson;
2
3 import java.lang.management.managementfactory;
4 import java.net.inetaddress;
5 import java.net.networkinterface;
6
7 //雪花算法代码实现
8 public class idworker {
9 // 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）
10 private final static long twepoch = 1288834974657l;
11 // 机器标识位数
12 private final static long workeridbits = 5l;
13 // 数据中心标识位数
14 private final static long datacenteridbits = 5l;
15 // 机器id最大值
16 private final static long maxworkerid = -1l ^ (-1l << workeridbits);
17 // 数据中心id最大值
18 private final static long maxdatacenterid = -1l ^ (-1l << datacenteridbits);
19 // 毫秒内自增位
20 private final static long sequencebits = 12l;
21 // 机器id偏左移12位
22 private final static long workeridshift = sequencebits;
23 // 数据中心id左移17位
24 private final static long datacenteridshift = sequencebits + workeridbits;
25 // 时间毫秒左移22位
26 private final static long timestampleftshift = sequencebits + workeridbits + datacenteridbits;
27
28 private final static long sequencemask = -1l ^ (-1l << sequencebits);
29 /* 上次生产id时间戳 */
30 private static long lasttimestamp = -1l;
31 // 0，并发控制
32 private long sequence = 0l;
33
34 private final long workerid;
35 // 数据标识id部分
36 private final long datacenterid;
37
38 public idworker(){
39 this.datacenterid = getdatacenterid(maxdatacenterid);
40 this.workerid = getmaxworkerid(datacenterid, maxworkerid);
41 }
42 /**
43 * @param workerid
44 * 工作机器id
45 * @param datacenterid
46 * 序列号
47 */
48 public idworker(long workerid, long datacenterid) {
49 if (workerid > maxworkerid || workerid < 0) {
50 throw new illegalargumentexception(string.format("worker id can't be greater than %d or less than 0", maxworkerid));
51 }
52 if (datacenterid > maxdatacenterid || datacenterid < 0) {
53 throw new illegalargumentexception(string.format("datacenter id can't be greater than %d or less than 0", maxdatacenterid));
54 }
55 this.workerid = workerid;
56 this.datacenterid = datacenterid;
57 }
58 /**
59 * 获取下一个id
60 *
61 * @return
62 */
63 public synchronized long nextid() {
64 long timestamp = timegen();
65 if (timestamp < lasttimestamp) {
66 throw new runtimeexception(string.format("clock moved backwards. refusing to generate id for %d milliseconds", lasttimestamp - timestamp));
67 }
68
69 if (lasttimestamp == timestamp) {
70 // 当前毫秒内，则+1
71 sequence = (sequence + 1) & sequencemask;
72 if (sequence == 0) {
73 // 当前毫秒内计数满了，则等待下一秒
74 timestamp = tilnextmillis(lasttimestamp);
75 }
76 } else {
77 sequence = 0l;
78 }
79 lasttimestamp = timestamp;
80 // id偏移组合生成最终的id，并返回id
81 long nextid = ((timestamp - twepoch) << timestampleftshift)
82 | (datacenterid << datacenteridshift)
83 | (workerid << workeridshift) | sequence;
84
85 return nextid;
86 }
87
88 private long tilnextmillis(final long lasttimestamp) {
89 long timestamp = this.timegen();
90 while (timestamp <= lasttimestamp) {
91 timestamp = this.timegen();
92 }
93 return timestamp;
94 }
95
96 private long timegen() {
97 return system.currenttimemillis();
98 }
99
100 /**
101 * <p>
102 * 获取 maxworkerid
103 * </p>
104 */
105 protected static long getmaxworkerid(long datacenterid, long maxworkerid) {
106 stringbuffer mpid = new stringbuffer();
107 mpid.append(datacenterid);
108 string name = managementfactory.getruntimemxbean().getname();
109 if (!name.isempty()) {
110 /*
111 * get jvmpid
112 */
113 mpid.append(name.split("@")[0]);
114 }
115 /*
116 * mac + pid 的 hashcode 获取16个低位
117 */
118 return (mpid.tostring().hashcode() & 0xffff) % (maxworkerid + 1);
119 }
120
121 /**
122 * <p>
123 * 数据标识id部分
124 * </p>
125 */
126 protected static long getdatacenterid(long maxdatacenterid) {
127 long id = 0l;
128 try {
129 inetaddress ip = inetaddress.getlocalhost();
130 networkinterface network = networkinterface.getbyinetaddress(ip);
131 if (network == null) {
132 id = 1l;
133 } else {
134 byte[] mac = network.gethardwareaddress();
135 id = ((0x000000ff & (long) mac[mac.length - 1])
136 | (0x0000ff00 & (((long) mac[mac.length - 2]) << 8))) >> 6;
137 id = id % (maxdatacenterid + 1);
138 }
139 } catch (exception e) {
140 system.out.println(" getdatacenterid: " + e.getmessage());
141 }
142 return id;
143 }
144 }
package com.anson;
/**
* @description: todo
* @author: anson
* @date: 2019/10/7 22:16
* @version: 1.0
*/
public class snow
{
public static void main(string[] args) throws exception
{
try
{
idworker idw = new idworker(1,1);
long ids = idw.nextid();
for(int i=0;i<10000;i++)
{
ids = idw.nextid();
system.out.println(ids);
}
}
catch (exception ex)
{
}
}
}
结果如下图：
程序生成了19位的有序数字，这个既解决了分布式id生成唯一性问题，也解决了性能问题，建议系统id设计都采用该算法生成。
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