用ConcurrentHashMap作缓存

// 用map实现一个简单的缓存功能
public class MapCacheDemo {

    // 我使用了  ConcurrentHashMap，线程安全的要求。
    //我使用SoftReference   作为映射值，因为软引用可以保证在抛出OutOfMemory之前，如果缺少内存，将删除引用的对象。
    //在构造函数中，我创建了一个守护程序线程，每5秒扫描一次并清理过期的对象。
    private static final int CLEAN_UP_PERIOD_IN_SEC = 5;

  private static ScheduledThreadPoolExecutor scheduledThreadPoolExecutor = new ScheduledThreadPoolExecutor(1);
  private final ConcurrentHashMap<String, SoftReference<CacheObject>> cache = new ConcurrentHashMap<>();

    public MapCacheDemo() {
        scheduledThreadPoolExecutor.setThreadFactory(new ThreadFactoryBuilder()
                .setNameFormat("demo-pool-%d").build());
        scheduledThreadPoolExecutor.scheduleAtFixedRate(()->cache.entrySet().removeIf(entry -> Optional.ofNullable(entry.getValue()).map(SoftReference::get).map(CacheObject::isExpired).orElse(false)),
                5,5,TimeUnit.SECONDS);
    }

    public void add(String key, Object value, long periodInMillis) {
        if (key == null) {
            return;
        }
        if (value == null) {
            cache.remove(key);
        } else {
            long expiryTime = System.currentTimeMillis() + periodInMillis;
            cache.put(key, new SoftReference<>(new CacheObject(value, expiryTime)));
        }
    }

    public void remove(String key) {
        cache.remove(key);
    }

    public Object get(String key) {
        return Optional.ofNullable(cache.get(key)).map(SoftReference::get).filter(cacheObject -> !cacheObject.isExpired()).map(CacheObject::getValue).orElse(null);
    }

    public void clear() {
        cache.clear();
    }

    public long size() {
        return cache.entrySet().stream().filter(entry -> Optional.ofNullable(entry.getValue()).map(SoftReference::get).map(cacheObject -> !cacheObject.isExpired()).orElse(false)).count();
    }

    // 缓存对象value
    private static class CacheObject {
        private Object value;
        private long expiryTime;

        private CacheObject(Object value, long expiryTime) {
            this.value = value;
            this.expiryTime = expiryTime;
        }

        boolean isExpired() {
            return System.currentTimeMillis() > expiryTime;
        }

        public Object getValue() {
            return value;
        }

        public void setValue(Object value) {
            this.value = value;
        }
    }
}

 

本文地址：https://blog.csdn.net/xx897115293/article/details/110263299