缓存demo

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package cn.itcast.heima;import java.util.HashMap;import java.util.Map;import java.util.concurrent.locks.ReadWriteLock;import java.util.concurrent.locks.ReentrantReadWriteLock;/** * 缓存demo *  * @ClassName: CacheDemo * @Description: TODO * @author liuyuan * @date 2016年8月10日 下午6:53:07 */public class CacheDemo {    private Map<String, Object> cache = new HashMap<String, Object>();// 缓存存放的位置    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();// 读写锁    public Object getData(String key) {        readWriteLock.readLock().lock();// 加读锁        Object value = null;        try {            value = cache.get(key);// 读            if (value == null) {                readWriteLock.readLock().unlock();// 开读锁                readWriteLock.writeLock().lock();// 加写锁                try {                    if (value == null) {                        value = "abc";// 写：实际代码为从数据库中查询;                    }                } catch (Exception e) {                    e.printStackTrace();                } finally {                    readWriteLock.writeLock().unlock();// 开写锁                }                readWriteLock.readLock().lock();// 加读锁            }        } catch (Exception e) {            e.printStackTrace();        } finally {            readWriteLock.readLock().unlock();// 开读锁        }        return value;    }}
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