标准缓存系统--JAVA读写锁的使用

package cn.itcast.heima2;


import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;


/**
 * 多线程下的缓存系统<br>
 * 高效率的缓存系统，防止多线程重复写操作
 * @author RSun
 * @Date 2013-4-5上午12:00:57
 */
public class CacheDemo {


private Map<String, Object> cache = new HashMap<String, Object>();


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{
// 防止多个线程同时上写锁
if(value==null){
value = "aaaa";//实际queryDB();
}
}finally{
rwl.writeLock().unlock();
}
rwl.readLock().lock();
}
}finally{
rwl.readLock().unlock();
}
return value;
}
}