并发——读写锁实现缓存

我不是女神ヾ 2022-10-27 02:17 150阅读 0赞

利用读写锁，完成缓存数据读写，减少db压力。

import java.util.HashMap;
    import java.util.Map;
    import java.util.concurrent.locks.ReentrantReadWriteLock;
    
    public class ReadWriteCache {
    
        // 锁
        private ReentrantReadWriteLock reentrantReadWriteLock = new ReentrantReadWriteLock();
    
        private Map<String, Object> cache = new HashMap<>();
    
        public Object getData(String key) {
            // 获取读锁
            reentrantReadWriteLock.readLock().lock();
            try {
                Object result = cache.get(key);
                if (result != null) {
                    return result;
                }
                // 释放读锁
                reentrantReadWriteLock.readLock().unlock();
                // 获取写锁
                reentrantReadWriteLock.writeLock().lock();
                try {
                    if (cache.get(key) != null) {
                        System.out.println("get from cache:" + key);
                        return cache.get(key);
                    }
                    result = getFromDb(key);
                    cache.put(key, result);
                    return result;
                } finally {
                    // 获取读锁，进行锁降级
                    reentrantReadWriteLock.readLock().lock();
                    // 释放写锁
                    reentrantReadWriteLock.writeLock().unlock();
                }
    
            } finally {
                // 释放读锁
                reentrantReadWriteLock.readLock().unlock();
            }
        }
    
        public Object getFromDb(String key) {
            return System.currentTimeMillis() + "_" + key;
        }
    
        public static void main(String[] args) {
            ReadWriteCache readWriteCache = new ReadWriteCache();
            Object result = readWriteCache.getData("a");
            System.out.println(result);
            result = readWriteCache.getData("a");
            System.out.println(result);
    
            result = readWriteCache.getData("b");
            System.out.println(result);
            result = readWriteCache.getData("b");
            System.out.println(result);
        }
    
    }