这个名字老记不住，一到用的时候就想不起来，还得翻以前的项目各种找。。。

在此特此记录吧

1 public class IDFactory {  2   3     private static final Logger LOGGER = LoggerFactory.getLogger(IDFactory.class);  4     /**  5      * 使用Bitset标记所有已使用的id
  6      * 不限定大小，以至于能达到 {
    @link Integer#MAX_VALUE}  7      */  8     private final BitSet idList;  9  10     /** 11      * 同步锁 12      */ 13     private final ReentrantLock lock; 14  15     /** 16      * 标记下一个int的索引 17      */ 18     private volatile int nextIndex = 0; 19  20     private IDFactory() { 21         idList = new BitSet(); 22         lock = new ReentrantLock(); 23         lockIds(0); 24  25         LOGGER.info("IDFactory: " + getUsedCount() + " id's used."); 26     } 27  28     private static class SingletonHolder { 29         protected static final IDFactory INSTANCE = new IDFactory(); 30     } 31  32     public static final IDFactory getInstance() { 33         return SingletonHolder.INSTANCE; 34     } 35  36     /** 37      * 下一个可用的int值 38      *  39      * @return 40      */ 41     public int nextId() { 42         try { 43             lock.lock(); 44  45             int id; 46             if (nextIndex == Integer.MIN_VALUE) { 47                 id = Integer.MIN_VALUE; 48             } else { 49                 id = idList.nextClearBit(nextIndex); 50             } 51  52             // 当id超过Integer#MAX_VALUE后的下一个int值将是Integer#MIN_VALUE，即已经用光了 53             if (id == Integer.MIN_VALUE) { 54                 LOGGER.error("All id's are used!",new Exception("All id's are used!")); 55             } 56             idList.set(id); 57  58             // It ok to have Integer OverFlow here, on next ID request IDFactory 59             // will throw error 60             nextIndex = id + 1; 61             return id; 62         } finally { 63             lock.unlock(); 64         } 65     } 66  67     /** 68      * 告诉生成器已使用了那些int值 69      *  70      * @param ids 71      *            ids to lock 72      */ 73     private void lockIds(int... ids) { 74         try { 75             lock.lock(); 76             for (int id : ids) { 77                 boolean status = idList.get(id); 78                 if (status) { 79                     LOGGER.error("ID " + id + " is already taken, fatal error!",new Exception("ID " + id + " is already taken, fatal error!")); 80                 } 81                 idList.set(id); 82             } 83         } finally { 84             lock.unlock(); 85         } 86     } 87  88     /** 89      * 告诉生成器已使用了那些int值 90      *  91      * @param ids 92      *            ids to lock 93      */ 94     public void lockIds(Iterable
     
       ids) { 95         try { 96             lock.lock(); 97             for (int id : ids) { 98                 boolean status = idList.get(id); 99                 if (status) {100                     LOGGER.error("ID " + id + " is already taken, fatal error!",new Exception("ID " + id + " is already taken, fatal error!"));101                 }102                 idList.set(id);103             }104         } finally {105             lock.unlock();106         }107     }108 109     /**110      * 告诉生成器某int值可以重新使用111      * 112      * @param id113      *            id to release114      */115     public void releaseId(int id) {116         try {117             lock.lock();118             boolean status = idList.get(id);119             if (!status) {120                 LOGGER.error("ID " + id + " is not taken, can't release it.",new Exception("ID " + id + " is not taken, can't release it."));121             }122             idList.clear(id);123             if (id < nextIndex || nextIndex == Integer.MIN_VALUE) {124                 nextIndex = id;125             }126         } finally {127             lock.unlock();128         }129     }130 131     /**132      * 已使用的int数133      * 134      * @return 已使用的int数135      */136     public int getUsedCount() {137         try {138             lock.lock();139             return idList.cardinality();140         } finally {141             lock.unlock();142         }143     }144 }
     

最适合用他的场景就是游戏中各种物体怪物之类的id