写一个缓存系统的伪代码

import java.util.HashMap; import java.util.Map; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock; public class CatchDemo { private Map<String, Object> cache = new HashMap<String, Object>(); public static void main(String[] args) { } //ReadWriteLock //读锁与读锁不互斥，读锁与写锁，写所欲写锁互斥 // 线程安全 // 向数据库查询数据时，先查缓存系统，若有，则返回 // 若没有，则从数据库查询数据写入缓存，再读取 private ReadWriteLock rwl = new ReentrantReadWriteLock(); public /* synchronized */ Object getData(String key) { rwl.readLock().unlock(); Object obj = null; try { obj = cache.get(key); if (obj == null) { rwl.readLock().unlock(); rwl.writeLock().lock(); try { if(obj == null) obj = "aaa";// 实际上是queryDB } finally { rwl.writeLock().unlock(); } rwl.readLock().lock(); } } catch (Exception e) { e.printStackTrace(); } finally { rwl.readLock().unlock(); } return obj; } }