java模拟数据库缓存

实现缓存一些数据到本地，避免重复查询数据库，对数据库造成压力，代码如下：

package threadLock;

import java.util.HashMap;

import java.util.Map;

import java.util.concurrent.locks.ReadWriteLock;

import java.util.concurrent.locks.ReentrantReadWriteLock;

public class CatheDemo {

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

    private ReadWriteLock rwl = new ReentrantReadWriteLock(); //定义读写锁

    public Object getData(String key){

        rwl.readLock().lock();

        Object value = null;

        try {

            value = map.get(key);

            if (value ==  null) {

                rwl.readLock().unlock();

                rwl.writeLock().lock();

                try {

                    if(value == null)

                        value = "dqwdwqd"; //从数据库中查找数据

                } catch (Exception e) {

                    e.printStackTrace();

                }finally{

                    rwl.writeLock().unlock();

                    rwl.readLock().lock();

                }

            }

        } catch (Exception e) {

            e.printStackTrace();

        }finally{

            rwl.readLock().unlock();

        }

        return value;

    }

}