有没有办法修改以声明方式声明的 JCache 的过期策略？

Question

我正在使用 Hazelcast 3.12 jCache 实现。我的缓存已声明声明（通过 hazelcast-config.xml），但是我希望能够动态更改 ExpiryPolicy 的持续时间，因为超时值只能通过编程方式获得。

我查看了 ICache 的文档，但没有看到任何方法可以让我检索 and/or 修改整个缓存的过期策略。

我的缓存声明为：

<cache name="toto">
    <async-backup-count>1</async-backup-count>
    <backup-count>1</backup-count>
    <cache-entry-listeners>
        <cache-entry-listener old-value-required="true">
            <cache-entry-listener-factory class-name="cache.UserRolesEntryListenerStaticFactory"/>
        </cache-entry-listener>
    </cache-entry-listeners>
    <key-type class-name="java.lang.String"/>
    <management-enabled>true</management-enabled>
    <statistics-enabled>true</statistics-enabled>
    <quorum-ref>1</quorum-ref>
    <partition-lost-listeners></partition-lost-listeners>
</cache>

我想 set/update 检索时的过期政策为：

@Produces
@Singleton
@UserRolesCache
public Cache<String, String[]> createUserRoleCache(@HazelcastDistributed CacheManager cacheManager) {
    Cache cache = cacheManager.getCache("toto");

    // get expiry timeout from a 3rd service
    int timeout = configService.getCacheExpiry();

    // how to set the expiry policy here???
    // cache.setExpiryPolicy(.....) ?????
}

使用 jCache 或 Hazelcast API 这可行吗？

Answer 1

没有明确的方法来更改 Cache 的默认过期策略（在 JCache 或 Hazelcast 特定 APIs).

您可以通过使用自定义 Factory<ExpiryPolicy> 配置 Cache 来达到相同的效果。在您的 ExpiryPolicy 实施中，您可以咨询您的外部服务以查询当前到期持续时间和 return 以便 JCache 实现应用它。请注意，由于过期政策在每个条目creation/access/update上查询，最好ExpiryPolicy方法实现不涉及任何远程服务查询或数据库访问，否则您将遇到高延迟。例如，最好将您的过期政策注册为外部服务的侦听器（如果支持）或者有一个单独的执行程序来安排对外部服务的更新查询。

使用 JCache 的示例实现 API:

class Scratch {
    public static void main(String[] args)
            throws InterruptedException {
        MutableConfiguration<String, String[]> roleCacheConfig = new MutableConfiguration<>();
        // other config here...
        roleCacheConfig.setExpiryPolicyFactory(new CustomExpiryPolicyFactory());

        CachingProvider provider = Caching.getCachingProvider();
        CacheManager manager = provider.getCacheManager();
        Cache<String, String[]> cache = manager.createCache("test", roleCacheConfig);

        cache.put("a", new String[]{}); // consults getExpiryForCreation
        Thread.sleep(1000);
        cache.get("a"); // consults getExpiryForAccess
        Thread.sleep(1000);
        cache.put("a", new String[]{}); // consults getExpiryForUpdate
    }

    public static class CustomExpiryPolicyFactory implements Factory<ExpiryPolicy>, Serializable {
        @Override
        public ExpiryPolicy create() {
            // initialize custom expiry policy: at this point
            // the custom expiry policy should be registered as listener to
            // external service publishing expiry info or otherwise configured
            // to poll the external service for new expiry info
            CustomExpiryPolicy expiryPolicy = new CustomExpiryPolicy(120, 30, 120);
            return expiryPolicy;
        }
    }

    public static class CustomExpiryPolicy implements ExpiryPolicy {

        private volatile Duration expiryForCreation;
        private volatile Duration expiryForAccess;
        private volatile Duration expiryForUpdate;

        public CustomExpiryPolicy(long secondsForCreation,
                           long secondsForAccess,
                           long secondsForUpdate) {
            this.expiryForCreation = new Duration(TimeUnit.SECONDS, secondsForCreation);
            this.expiryForAccess = new Duration(TimeUnit.SECONDS, secondsForAccess);
            this.expiryForUpdate = new Duration(TimeUnit.SECONDS, secondsForUpdate);
        }

        // assuming this is invoked from external service whenever there is a change
        public void onExpiryChanged(long secondsForCreation,
                                    long secondsForAccess,
                                    long secondsForUpdate) {
            this.expiryForCreation = new Duration(TimeUnit.SECONDS, secondsForCreation);
            this.expiryForAccess = new Duration(TimeUnit.SECONDS, secondsForAccess);
            this.expiryForUpdate = new Duration(TimeUnit.SECONDS, secondsForUpdate);
        }

        @Override
        public Duration getExpiryForCreation() {
            return expiryForCreation;
        }

        @Override
        public Duration getExpiryForAccess() {
            return expiryForAccess;
        }

        @Override
        public Duration getExpiryForUpdate() {
            return expiryForUpdate;
        }
    }
}

您可以在声明式 Hazelcast XML 配置中提供您的自定义到期策略工厂 class 名称，如下所示：

<cache name="toto">
    <async-backup-count>1</async-backup-count>
    <backup-count>1</backup-count>
    ...
    <expiry-policy-factory class-name="com.example.cache.CustomExpirePolicyFactory" />
    ...
</cache>

作为旁注，ICache 中有一些方法，Hazelcast 特定的扩展 Cache 接口，允许您使用为每个键指定的自定义过期策略对一个或一组键执行操作（但不更改缓存范围内适用的过期策略）。

有没有办法修改以声明方式声明的 JCache 的过期策略？

Is there a way to modify a JCache's expiry policy that has been declared declaratively?

hazelcast

jcache

jsr107