# 发号器功能增强，对时间回撤有更强的处理能力。

1. 使用缓存存储 120 秒内的计数器。当时间回撤低于 120 秒时，到缓存中找计数器。
2. 使用 AtomicInteger 替换 synchronized 关键字保证原子性。
3. 现在性能大约每秒 13w

src/main/java/cn/quantgroup/xyqb/Utils/IDGenerator.java

 package cn.quantgroup.xyqb.Utils;
 
+import com.google.common.cache.CacheBuilder;
+import com.google.common.cache.CacheLoader;
+import com.google.common.cache.LoadingCache;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.data.redis.core.StringRedisTemplate;
@@ -9,21 +14,30 @@ import javax.annotation.PostConstruct;
 import java.text.SimpleDateFormat;
 import java.util.Date;
 import java.util.Locale;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 
 /**
  * 注意事项：
  * 1. 使用前在配置文件内配置 DATA_CENTER_ID
- *
- *
+ * <p>
+ * <p>
  * Created by zhiguo.liu on 2017/5/18.
  */
 @Component
 public class IDGenerator {
 
+    private static final Logger LOGGER = LoggerFactory.getLogger(IDGenerator.class);
+
 
     private static final String REDIS_WORK_ID_KEY = "GLOBAL:WORK:ID:";
     private static final String ID_FORMAT = "yyyyMMddHHmmss";
 
+    private static Lock lock = new ReentrantLock();
+
     // data center，默认为 1
     private static int DATA_CENTER_ID = 1;
     private static int WORKER_ID = 0;
@@ -32,15 +46,31 @@ public class IDGenerator {
     // 最高每秒发号 100w
     private static final int MAX_COUNT = 999999;
 
-    private static long COUNTER = 0L;
-    private static long MAX_TIME_SECOND = 0L;
+    private static AtomicInteger COUNTER = new AtomicInteger(0);
+    private static long MAX_TIME_SECOND;
 
-    // 当前时间戳字符串
-    private static String CURRENT_TIME_STR;
     // Worker ID 字符串
     private static String WORKER_ID_STR;
     // data center 字符串
     private static String DATA_CENTER_STR;
+    // 最长回退时间，120 秒
+    private static int MAX_BACK_SECOND = 120;
+    static{
+        Date now = new Date();
+        Long timeSecond = now.getTime() / 1000;
+        MAX_TIME_SECOND = timeSecond;
+
+    }
+
+    private static LoadingCache cache = CacheBuilder.newBuilder()
+            .expireAfterWrite(MAX_BACK_SECOND, TimeUnit.SECONDS)
+            .build(new CacheLoader<Long, AtomicInteger>() {
+                @Override
+                public AtomicInteger load(Long key) throws Exception {
+                    return new AtomicInteger(0);
+                }
+            });
+
 
     @Autowired
     private StringRedisTemplate redis;
@@ -53,7 +83,6 @@ public class IDGenerator {
     @PostConstruct
     public void init() {
         WORKER_ID = (int) (redis.opsForValue().increment(REDIS_WORK_ID_KEY + DATA_CENTER_ID, 1) % MAX_WORK_ID);
-
         WORKER_ID_STR = String.format("%04d", WORKER_ID);
         DATA_CENTER_STR = String.format("%03d", DATA_CENTER_ID);
     }
@@ -62,26 +91,48 @@ public class IDGenerator {
     /**
      * 1. 需要获取 dataCenterId 和 workeId
      */
-    public synchronized static String getId(String prefix) {
+    public static String getId(String prefix) {
         Date now = new Date();
         Long timeSecond = now.getTime() / 1000;
+
+        Integer counter = 0;
         if (timeSecond > MAX_TIME_SECOND) {
-            MAX_TIME_SECOND = timeSecond;
-            CURRENT_TIME_STR = new SimpleDateFormat(ID_FORMAT, Locale.SIMPLIFIED_CHINESE).format(now);
-            COUNTER = 0;
+            lock.lock();
+            if(timeSecond > MAX_TIME_SECOND){
+                cache.put(MAX_TIME_SECOND, COUNTER);
+                COUNTER = new AtomicInteger(0);
+                MAX_TIME_SECOND = timeSecond;
+            }
+            lock.unlock();
+        }
+        if(timeSecond == MAX_TIME_SECOND){
+            counter = COUNTER.incrementAndGet();
+        }
+        // 时间回退时到 cache 里拿，或者直接抛出错误
+        if (timeSecond < MAX_TIME_SECOND) {
+            if (timeSecond + MAX_BACK_SECOND < MAX_TIME_SECOND) {
+                throw new RuntimeException("时间回撤, 请稍后再试");
+            }
+            try {
+                AtomicInteger historyCounter = (AtomicInteger) cache.get(timeSecond);
+                counter = historyCounter.incrementAndGet();
+            } catch (ExecutionException e) {
+                LOGGER.error("取出缓存时出错");
+            }
         }
 
-        // 达到计数器上上限，或时间回退时, 休眠半秒并重试
-        if (COUNTER >= MAX_COUNT || timeSecond < MAX_TIME_SECOND) {
+        // 达到计数器上上限, 休眠半秒并重试
+        if (counter >= MAX_COUNT) {
             try {
                 Thread.sleep(500);
                 return getId(prefix);
             } catch (InterruptedException e) {
-                e.printStackTrace();
+                LOGGER.error("发号器休眠时发生错误:{}", e);
             }
         }
 
-        return prefix + CURRENT_TIME_STR + DATA_CENTER_STR + WORKER_ID_STR + String.format("%06d", ++COUNTER);
+        String currentTimeStr = new SimpleDateFormat(ID_FORMAT, Locale.SIMPLIFIED_CHINESE).format(now);
+        return prefix + currentTimeStr + DATA_CENTER_STR + WORKER_ID_STR + String.format("%06d", counter);
     }
 
 }