Map locks = new Map();
 List lockKeys = new List();
for (int number : 1 - 10000) {
 Object lockKey = new Object();
 lockKeys.add(lockKey);
 locks.put(lockKey, new Object());
}
public void doSomeThing(String uid) {
 Object lockKey = lockKeys.get(uid.hash() % lockKeys.size());
 Object lock = locks.get(lockKey);
 synchronized(lock) {
  // do something
 }
}

public class LockPool {
 //用户map
 private static ConcurrentHashMap<String,Object> userMap=new ConcurrentHashMap<String,Object>();
 //用户金额map
 private static ConcurrentHashMap<String,Integer> moneyMap=new ConcurrentHashMap<String,Integer>();
 public static void main(String[] args) {
  LockPool lockPool=new LockPool();
  ExecutorService service = Executors.newCachedThreadPool();
  service.execute(lockPool.new Boss("u2"));
  service.execute(lockPool.new Boss("u1"));
  service.execute(lockPool.new Boss("u1"));
  service.execute(lockPool.new Boss("u3"));
  service.execute(lockPool.new Boss("u2"));
  service.execute(lockPool.new Boss("u2"));
  service.execute(lockPool.new Boss("u3"));
  service.execute(lockPool.new Boss("u2"));
  service.execute(lockPool.new Boss("u2"));
  service.execute(lockPool.new Boss("u4"));
  service.execute(lockPool.new Boss("u2"));
  service.shutdown();
 }
 class Boss implements Runnable{
  private String userId;
  Boss(String userId){
   this.userId=userId;
  }
  @Override
      public void run() {
   addMoney(userId);
  }
 }
 public static void addMoney(String userId){
  Object obj=userMap.get(userId);
  if(obj==null){
   obj=new Object();
   userMap.put(userId,obj);
  }
  //obj是与具体某个用户绑定，这里应用了synchronized(obj)的小技巧，而不是同步当前整个对象
  synchronized (obj) {
   try {
    System.out.println("-------sleep4s--------"+userId);
    Thread.sleep(4000);
    System.out.println("-------awake----------"+userId);
   }
   catch (InterruptedException e) {
    e.printStackTrace();
   }
   if(moneyMap.get(userId)==null){
    moneyMap.put(userId,1);
   } else{
    moneyMap.put(userId, moneyMap.get(userId)+1);
   }
   System.out.println(userId+"-------moneny----------"+moneyMap.get(userId));
  }
 }
}

-------sleep4s--------u2
-------sleep4s--------u1
-------sleep4s--------u3
-------sleep4s--------u4
-------awake----------u2
-------awake----------u3
-------awake----------u1
u2-------moneny----------1
u1-------moneny----------1
-------sleep4s--------u1
u3-------moneny----------1
-------sleep4s--------u2
-------sleep4s--------u3
-------awake----------u4
u4-------moneny----------1
-------awake----------u1
u1-------moneny----------2
-------awake----------u3
u3-------moneny----------2
-------awake----------u2
u2-------moneny----------2
-------sleep4s--------u2
-------awake----------u2
u2-------moneny----------3
-------sleep4s--------u2
-------awake----------u2
u2-------moneny----------4
-------sleep4s--------u2
-------awake----------u2
u2-------moneny----------5
-------sleep4s--------u2
-------awake----------u2
u2-------moneny----------6