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;
	}
}