缓存类

package com.test;import java.util.HashMap;import java.util.Map;import java.util.concurrent.locks.ReentrantReadWriteLock;public class Cache{Map map = new HashMap();ReentrantReadWriteLock lock = new ReentrantReadWriteLock();public Object get(String key){lock.readLock().lock();Object obj;try{obj = map.get(key);if(obj == null){lock.readLock().unlock();lock.writeLock().lock();obj = "rs";  //读数据库map.put(key, obj);lock.writeLock().unlock();lock.readLock().lock();}}finally{lock.readLock().unlock();}return obj;}}