我在這裏虧本。番石榴CacheLoader錯過
我已經真的很幸運,手動加載/插入Guava緩存,但我決定它應該更「線程安全」(通過CacheLoader)。
當我重構爲使用CacheLoader.load樣式語法時,我的緩存停止工作。每個get()現在都是一個緩存缺失,並開始調用load()。
我錯過了一些非常簡單的東西嗎?
緩存:
public class DatabasePropertyCache implements RemovalListener<DatabasePropertyCache.Key, Optional<Object>> {
//InitializeOnDemand style singleton
// http://en.wikipedia.org/wiki/Singleton_pattern#Initialization_On_Demand_Holder_Idiom
private static class Singleton {
static DatabasePropertyCache INSTANCE = new DatabasePropertyCache();
}
public static DatabasePropertyCache getInstance() {
return Singleton.INSTANCE;
}
private DatabasePropertyCache() {
logger = Logger.getLogger(DatabasePropertyCache.class);
cache = CacheBuilder
.newBuilder()
.expireAfterWrite(24, TimeUnit.HOURS)
.removalListener(this)
.build(
new CacheLoader<Key, Optional<Object>>() {
@Override
public Optional<Object> load(Key key) throws Exception {
Object propertyValue = [performs a query]
return Optional.fromNullable(propertyValue);
}
});
}
private final LoadingCache<Key, Optional<Object>> cache;
private final Logger logger;
public void onRemoval(RemovalNotification<Key, Optional<Object>> arg0) {
if(logger.isDebugEnabled()) {
logger.debug(String.format("Cached database property expiring %s", arg0.getKey().toString()));
}
}
/**
* Returns a cached value. If it has never been cache before, it will be fetched from the database.
*
* @param value
* @param locale
* @param dataset
* @return
*/
public Object getObject(String id, DatabasePropertiesEnum property, Locale locale) {
Key key = new Key(id, property, locale);
try {
return cache.get(key).orNull();
}
catch (ExecutionException eex) {
logger.warn(String.format("Error fetching database property %s", key.toString()), eex);
}
return null;
}
protected class Key {
private static final String TOSTRING_TEMPLATE = "DatabasePropertyCache.Key[dataset=%s, locale=%s, property=%s]";
private String id;
private DatabasePropertiesEnum property;
private Locale locale;
public Key(String id, DatabasePropertiesEnum property, Locale locale) {
this.id= id;
this.property = property;
this.locale = locale;
}
@Override
public int hashCode() {
return new HashCodeBuilder()
.append(this.id)
.append(this.property)
.append(this.locale)
.toHashCode();
}
public String getId() {
return id;
}
public DatabasePropertiesEnum getProperty() {
return property;
}
public Locale getLocale() {
return locale;
}
@Override
public String toString() {
return String.format(TOSTRING_TEMPLATE, id, locale.toString(), property.name());
}
}
}
用法:
Object cacheHit = DatabasePropertyCache.getInstance().getObject("some_id", DatabasePropertiesEnum.SOME_KEY, [users current locale]);
所以,是的,我失去了一些東西真的很簡單。我們以前的實現使用int(通過.hashCode())作爲鍵,因此是錯誤。謝謝! –