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  1. /**
  2. * twitter的snowflake算法 -- java实现
  3. *
  4. * @author beyond
  5. * @date 2016/11/26
  6. */
  7. public class SnowFlake {
  8.  
  9. /**
  10. * 起始的时间戳
  11. */
  12. private final static long START_STMP = 1480166465631L;
  13.  
  14. /**
  15. * 每一部分占用的位数
  16. */
  17. private final static long SEQUENCE_BIT = 12; //序列号占用的位数
  18. private final static long MACHINE_BIT = 5; //机器标识占用的位数
  19. private final static long DATACENTER_BIT = 5;//数据中心占用的位数
  20.  
  21. /**
  22. * 每一部分的最大值
  23. */
  24. private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
  25. private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
  26. private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);
  27.  
  28. /**
  29. * 每一部分向左的位移
  30. */
  31. private final static long MACHINE_LEFT = SEQUENCE_BIT;
  32. private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
  33. private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
  34.  
  35. private long datacenterId; //数据中心
  36. private long machineId; //机器标识
  37. private long sequence = 0L; //序列号
  38. private long lastStmp = -1L;//上一次时间戳
  39.  
  40. public SnowFlake(long datacenterId, long machineId) {
  41. if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
  42. throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
  43. }
  44. if (machineId > MAX_MACHINE_NUM || machineId < 0) {
  45. throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
  46. }
  47. this.datacenterId = datacenterId;
  48. this.machineId = machineId;
  49. }
  50.  
  51. /**
  52. * 产生下一个ID
  53. *
  54. * @return
  55. */
  56. public synchronized long nextId() {
  57. long currStmp = getNewstmp();
  58. if (currStmp < lastStmp) {
  59. throw new RuntimeException("Clock moved backwards. Refusing to generate id");
  60. }
  61.  
  62. if (currStmp == lastStmp) {
  63. //相同毫秒内,序列号自增
  64. sequence = (sequence + 1) & MAX_SEQUENCE;
  65. //同一毫秒的序列数已经达到最大
  66. if (sequence == 0L) {
  67. currStmp = getNextMill();
  68. }
  69. } else {
  70. //不同毫秒内,序列号置为0
  71. sequence = 0L;
  72. }
  73.  
  74. lastStmp = currStmp;
  75.  
  76. return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
  77. | datacenterId << DATACENTER_LEFT //数据中心部分
  78. | machineId << MACHINE_LEFT //机器标识部分
  79. | sequence; //序列号部分
  80. }
  81.  
  82. private long getNextMill() {
  83. long mill = getNewstmp();
  84. while (mill <= lastStmp) {
  85. mill = getNewstmp();
  86. }
  87. return mill;
  88. }
  89.  
  90. private long getNewstmp() {
  91. return System.currentTimeMillis();
  92. }
  93.  
  94. public static void main(String[] args) {
  95. SnowFlake snowFlake = new SnowFlake(2, 3);
  96.  
  97. for (int i = 0; i < (1 << 12); i++) {
  98. System.out.println(snowFlake.nextId());
  99. }
  100.  
  101. }
  102. }
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