public class SnowFlake {
 // 起始的時(shí)間戳
 private final static long START_STMP = 1577808000000L; //2020-01-01
 // 每一部分占用的位數(shù)，就三個(gè)
 private final static long SEQUENCE_BIT = 12; //序列號(hào)占用的位數(shù)
 private final static long MACHINE_BIT = 5; //機(jī)器標(biāo)識(shí)占用的位數(shù)
 private final static long DATACENTER_BIT = 5; //數(shù)據(jù)中心占用的位數(shù)
 // 每一部分最大值
 private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
 private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
 private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);
 // 每一部分向左的位移
 private final static long MACHINE_LEFT = SEQUENCE_BIT;
 private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
 private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
 private long datacenterId; //數(shù)據(jù)中心
 private long machineId; //機(jī)器標(biāo)識(shí)
 private long sequence = 0L; //序列號(hào)
 private long lastStmp = -1L; //上一次時(shí)間戳

 public SnowFlake(long datacenterId, long machineId) {
  if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
   throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
  }
  if (machineId > MAX_MACHINE_NUM || machineId < 0) {
   throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
  }
  this.datacenterId = datacenterId;
  this.machineId = machineId;
 }

 //產(chǎn)生下一個(gè)ID
 public synchronized long nextId() {
  long currStmp = timeGen();
  if (currStmp < lastStmp) {
   throw new RuntimeException("Clock moved backwards. Refusing to generate id");
  }

  if (currStmp == lastStmp) {
   //if條件里表示當(dāng)前調(diào)用和上一次調(diào)用落在了相同毫秒內(nèi)，只能通過第三部分，序列號(hào)自增來判斷為唯一，所以+1.
   sequence = (sequence + 1) & MAX_SEQUENCE;
   //同一毫秒的序列數(shù)已經(jīng)達(dá)到最大，只能等待下一個(gè)毫秒
   if (sequence == 0L) {
    currStmp = getNextMill();
   }
  } else {
   //不同毫秒內(nèi)，序列號(hào)置為0
   //執(zhí)行到這個(gè)分支的前提是currTimestamp > lastTimestamp，說明本次調(diào)用跟上次調(diào)用對(duì)比，已經(jīng)不再同一個(gè)毫秒內(nèi)了，這個(gè)時(shí)候序號(hào)可以重新回置0了。
   sequence = 0L;
  }

  lastStmp = currStmp;
  //就是用相對(duì)毫秒數(shù)、機(jī)器ID和自增序號(hào)拼接
  return (currStmp - START_STMP) << TIMESTMP_LEFT //時(shí)間戳部分
    | datacenterId << DATACENTER_LEFT  //數(shù)據(jù)中心部分
    | machineId << MACHINE_LEFT    //機(jī)器標(biāo)識(shí)部分
    | sequence;        //序列號(hào)部分
 }

 private long getNextMill() {
  long mill = timeGen();
  while (mill <= lastStmp) {
   mill = timeGen();
  }
  return mill;
 }

 private long timeGen() {
  return System.currentTimeMillis();
 }
}

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {

 @Autowired
 public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
  converters.add(toStringConverter());
 }

 /**
  * BigDecimal Long 轉(zhuǎn)化為String
  *
  * @return
  */
 @Bean
 public MappingJackson2HttpMessageConverter toStringConverter() {
  MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
  ObjectMapper mapper = new ObjectMapper();
  SimpleModule simpleModule = new SimpleModule();
  simpleModule.addSerializer(BigDecimal.class, BigDecimalToStringSerializer.instance);
  simpleModule.addSerializer(Long.class, ToStringSerializer.instance);
  simpleModule.addSerializer(Long.TYPE, ToStringSerializer.instance);
  simpleModule.addSerializer(long.class, ToStringSerializer.instance);
  mapper.registerModule(simpleModule);
　　　　　// Include.Include.ALWAYS 默認(rèn)
　　　　　// Include.NON_DEFAULT 屬性為默認(rèn)值不序列化
　　　　　// Include.NON_EMPTY 屬性為 空（""） 或者為 NULL 都不序列化，則返回的json是沒有這個(gè)字段的。這樣對(duì)移動(dòng)端會(huì)更省流量
　　　　　// Include.NON_NULL 屬性為NULL 不序列化
　　　　　mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
　　　　　mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
　　　　　mapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_CONTROL_CHARS, true);// 允許出現(xiàn)特殊字符和轉(zhuǎn)義符
　　　　　mapper.configure(JsonParser.Feature.ALLOW_SINGLE_QUOTES, true); // 允許出現(xiàn)單引號(hào)

　　　　　converter.setObjectMapper(mapper);

　　　　　return converter;
 }

 @JacksonStdImpl
 static class BigDecimalToStringSerializer extends ToStringSerializer {
  public final static BigDecimalToStringSerializer instance = new BigDecimalToStringSerializer();

  public BigDecimalToStringSerializer() {
   super(Object.class);
  }

  public BigDecimalToStringSerializer(Class<?> handledType) {
   super(handledType);
  }

  @Override
  public boolean isEmpty(SerializerProvider prov, Object value) {
   if (value == null) {
    return true;
   }
   String str = ((BigDecimal) value).stripTrailingZeros().toPlainString();
   return str.isEmpty();
  }

  @Override
  public void serialize(Object value, JsonGenerator gen, SerializerProvider provider)
    throws IOException {
   gen.writeString(((BigDecimal) value).stripTrailingZeros().toPlainString());
  }

  @Override
  public JsonNode getSchema(SerializerProvider provider, Type typeHint) throws JsonMappingException {
   return createSchemaNode("string", true);
  }

  @Override
  public void serializeWithType(Object value, JsonGenerator gen,
          SerializerProvider provider, TypeSerializer typeSer)
    throws IOException {
   // no type info, just regular serialization
   serialize(value, gen, provider);
  }
 }
}