java中提供了lock锁，简便了设计缓存，下面程序主要是使用读写锁的应用。。。。
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
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{
if(value==null){
value = "aaaa";//这里可以到数据库中 提取，或者通过反射加载 }
}finally{
rwl.writeLock().unlock();
}
rwl.readLock().lock();
}
}finally{
rwl.readLock().unlock();
}
return value;
}
}