帶有生存時間的 EHcache 簡單示例

Question

我需要一個簡單的緩存來在內存中存儲具有特定生存時間的元組。 我在 EHcache 網站上找不到這樣做的方法，該網站主要包含復雜的使用場景。 任何人都可以幫助我嗎？

PS我不使用Spring。

Answer 1

Ehcache 2.x

程序化

CacheManager cacheManager = initCacheManager();
CacheConfiguration cacheConfiguration = new CacheConfiguration().name("myCache")
        .maxEntriesLocalHeap(100)
        .timeToLiveSeconds(20);
cacheManager.addCache(new Cache(cacheConfiguration));

XML

<cache name="myCache"
       maxEntriesLocalHeap="100"
       timeToLiveSeconds="20"/>

覆蓋每個Element

Ehcache 2.x 允許您覆蓋每個Element到期設置：

Element element = new Element("key", "value");
element.setTimeToLive(10);
cache.put(element);

Ehcache 3.x

程序化

CacheManager cacheManager = initCacheManager();
CacheConfigurationBuilder<Long, String> configuration = 
    CacheConfigurationBuilder.newCacheConfigurationBuilder(Long.class, String.class, ResourcePoolsBuilder
      .heap(100))
      .withExpiry(Expirations.timeToLiveExpiration(new Duration(20, TimeUnit.SECONDS)));
cacheManager.createCache("myCache", configuration);

在 Ehcache 3 中，構建器是不可變的，可以安全地共享以從類似的配置創建多個緩存。 如果您使用靜態導入，代碼會更加緊湊，我在這里沒有這樣做是為了簡化在 IDE 中粘貼此代碼段的過程。

XML

<cache alias="myCache">
  <expiry>
    <ttl unit="seconds">20</ttl>
  </expiry>
  <heap>100</heap>
</cache>

通過自定義Expiry覆蓋

在 Ehcache 3.x 中， Expiry是一個用戶可以實現的接口：

public interface Expiry<K, V> {
  Duration getExpiryForCreation(K key, V value);
  Duration getExpiryForAccess(K key, ValueSupplier<? extends V> value);
  Duration getExpiryForUpdate(K key, ValueSupplier<? extends V> oldValue, V newValue);
}

生存時間匹配getExpiryForCreation調用，它將接收映射的鍵和值，允許根據映射本身實現不同的到期時間。

Answer 2

Ehcache 3.x 解決方案在運行時定義每個元素的到期時間

此解決方案在 Ehcache 3.8.1 上測試正常，但代碼肯定對任何 Ehcache 3.x 都有效

首先創建一個類來保持一個泛型，實際上任何你可以傳遞給緩存的對象：

    import java.io.Serializable;
    import java.time.Duration;

    public class EhcacheValue<T> implements Serializable {

        private static final long serialVersionUID = 1L;

        private T object;

        private long timeToLive;

        public EhcacheValue(T theObject, Duration theDuration) {
            object = theObject;
            timeToLive = theDuration.getSeconds();
        }

        public Duration getTimeToLiveDuration() {
            return Duration.ofSeconds(timeToLive);
        }

        public T getObject() {
            return object;
        }

        public void setObject(T theObject) {
            object = theObject;
        }

        public long getTimeToLive() {
            return timeToLive;
        }

        public void setTimeToLive(long theTimeToLive) {
            timeToLive = theTimeToLive;
        }

    }

然后創建一個實現Ehcache 3.x接口ExpiryPolicy的自定義 Expiry 類：

import java.time.Duration;

import java.util.function.Supplier;

import org.ehcache.expiry.ExpiryPolicy;

public class CustomExpiryPolicy<K, V extends EhcacheValue<?>> implements ExpiryPolicy<K, V> {

    public CustomExpiryPolicy() {

    }

    @Override
    public Duration getExpiryForCreation(K theKey, V theValue) {
       return theValue.getTimeToLiveDuration();
    }

    @Override
    public Duration getExpiryForAccess(K theKey, Supplier<? extends V> theValue) {
        return null;
    }

    @Override
    public Duration getExpiryForUpdate(K theKey, Supplier<? extends V> theOldValue, V theNewValue) {
         return theNewValue.getTimeToLiveDuration();
       }
    }

然后你有正常的代碼，但有一些重要的行：

public class TestEhCache {

    private static final String CACHE_TIER_HEAP = "OnHeap";

    public static void main(String[] args) {

        StatisticsService statisticsService = new DefaultStatisticsService();

        myCacheManager = CacheManagerBuilder.newCacheManagerBuilder()
                .using(statisticsService)
                .build();

        //we init it here, not with boolean in build()
        myCacheManager.init();

        // Beware, the items are not expiring automatically, there are more mechanism in place for checking the expiration
        // For instance the expiration is checked at get time
        // for more details see the documentation from the version 2.8 
        // here: https://www.ehcache.org/documentation/2.8/apis/cache-event-listeners.html
        // Unfortunately for the version 3.x doesn't exist a detailed depiction, but in main the procedure is the same
        //
        // Ehcache 2.8 documentation:
        // Elements are checked for expiry in Ehcache at the following times:
        //
        // When a get request is made
        // When an element is spooled to the diskStore in accordance with a MemoryStore eviction policy
        // In the DiskStore when the expiry thread runs, which by default is
        // net.sf.ehcache.Cache#DEFAULT_EXPIRY_THREAD_INTERVAL_SECONDS

        CustomExpiryPolicy<String,EhcacheValue<?>> expiryPolicy = new CustomExpiryPolicy<String,EhcacheValue<?>>();

        ResourcePools resourcePools = ResourcePoolsBuilder.newResourcePoolsBuilder().heap(2000L, EntryUnit.ENTRIES).build();

        @SuppressWarnings("unchecked")
        Class<EhcacheValue<?>> myEhcacheValue = (Class<EhcacheValue<?>>)(Class<?>)EhcacheValue.class;

        CacheConfiguration<String,EhcacheValue<?>> cacheConfiguration = CacheConfigurationBuilder
                .newCacheConfigurationBuilder(String.class, myEhcacheValue, resourcePools)
                .withExpiry(expiryPolicy)
                //.withService(new StoreStatisticsConfiguration(true)) // explicitly enable statistics, it seems is not needed
                .build();

        myCache = myCacheManager.createCache("myCache", cacheConfiguration);

        myCacheStatistics = statisticsService.getCacheStatistics("myCache");

        long cacheEntriesNr = myCacheStatistics.getTierStatistics().get(CACHE_TIER_HEAP).getMappings();

        //nb element in heap tier
        long sizeEntriesByStatistics = myCacheStatistics.getTierStatistics().get("OnHeap").getMappings();
        //size of the tier in memory, when you set memory limits, not in this case
        //long sizeBytesByStatistics = myCacheStatistics.getTierStatistics().get("OnHeap").getOccupiedByteSize();

        long getsCnt = myCacheStatistics.getCacheGets();
        long putsCnt = myCacheStatistics.getCachePuts();
        long removalsCnt = myCacheStatistics.getCacheRemovals();
        long missesCnt = myCacheStatistics.getCacheMisses();
        long evictionsCnt = myCacheStatistics.getCacheEvictions();
        long crtExpiredCnt = myCacheStatistics.getCacheExpirations();

        System.out.println("getsCnt = "+getsCnt);
        System.out.println("putsCnt = "+putsCnt);
        System.out.println("removalsCnt = "+removalsCnt);
        System.out.println("missesCnt = "+missesCnt);
        System.out.println("evictionsCnt = "+evictionsCnt);
        System.out.println("expiredCnt = "+expiredCnt);
        System.out.println("hitPercentage = "+hitPercentage);
        System.out.println("missPercentage = "+missPercentage);
        System.out.println("Computed number of items in cache = "+(putsCnt-removalsCnt-expiredCnt-evictionsCnt));

    }

    @SuppressWarnings("unchecked")
    // we are aware about the unchecked cast - it is a desired behavior. 
    // Cache can store objects of various types, so compile time type safety cannot be achieved easily.
    // We'll get runtime ClassCastException if cache is used incorrectly.
    public static <T> T get(String key) {
        EhcacheValue<T> ehcacheValue = (EhcacheValue<T>)myCache.get(key);
        return (T) (ehcacheValue!=null?ehcacheValue.getObject():null);
    }

    // we are aware about the unchecked cast - it is a desired behavior. 
    // Cache can store objects of various types, so compile time type safety cannot be achieved easily.
    // We'll get runtime ClassCastException if cache is used incorrectly.
    public static <T extends Object> T put(String key, T value, int timeToLiveInSeconds) {

        if (key == null) {
            throw new AssertionError("Key must not be null!");
        }

        if (value != null) {
            EhcacheValue<T> ehcacheValue = new EhcacheValue<T>(value, Duration.of(60, ChronoUnit.SECONDS));
            myCache.put(key, ehcacheValue);
            return value;
        } else {
            return null;
        }
    }
}

Answer 3

對於 EhCache 3.3.1 版， groupId:org.ehcache,artifactId:ehcache ，以下有效！

CacheManager cacheManager = CacheManagerBuilder.newCacheManagerBuilder().withCache("AllCache",
        CacheConfigurationBuilder.newCacheConfigurationBuilder(String.class,String.class,
            ResourcePoolsBuilder.heap(100))
            .withExpiry(Expirations.timeToLiveExpiration(new Duration(86400, TimeUnit.SECONDS)))
            .build()).build(true);


Cache<String, String> allCache = cacheManager.getCache("AllCache", String.class, String.class);