基于读写锁的缓存demo

public class CacheDemo {private Map<String, Object> cache = new HashMap<String, Object>();public static void main(String[] args) {// TODO Auto-generated method stub}private ReadWriteLock rwl = new ReentrantReadWriteLock();public  Object getData(String key){rwl.readLock().lock();Object value = null;try{value = cache.get(key);if(value == null){rwl.readLock().unlock();rwl.writeLock().lock();try{if(value==null){value = "aaaa";//实际是去queryDB();}}finally{rwl.writeLock().unlock();}rwl.readLock().lock();}}finally{rwl.readLock().unlock();}return value;}}