ConcurrentHashMap如何在java项目中使用

import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import java.util.concurrent.ConcurrentHashMap;import java.util.concurrent.atomic.AtomicInteger;public class TestServiceImpl {  private static ConcurrentHashMap<Long, LockObj> lockMap = new ConcurrentHashMap<Long, LockObj>(40);  public void test(Long userId){    LockObj lock = tryLock(userId);    synchronized (lock) {      try{        //处理业务      }      finally{        unLock(lock);      }    }  }  private LockObj tryLock(Long key) {    LockObj curVal = new LockObj(key);    LockObj preVal = lockMap.putIfAbsent(key, curVal);    if (null == preVal) {      curVal.inc();      return curVal;    }    else{      preVal.inc();    }    return preVal;  }  private void unLock(LockObj lock){    if (lock.dec() <= 0){      lockMap.remove(lock.getKey());    }  }  public class LockObj {    private long key = 0;    private AtomicInteger count = new AtomicInteger(0);    public LockObj(long key){      this.key = key;    }    public int inc(){      return count.incrementAndGet();    }    public int dec(){      return count.decrementAndGet();    }    public long getKey(){      return key;    }    @Override    public String toString() {      return "LockObj [key=" + key + ", count=" + count + "]";    }  }}