[英]Guava CacheLoader Misses
我在這里茫然。
我真的很幸運,可以手動加載/插入到Guava緩存中,但是我認為它應該更“線程安全”(通過CacheLoader)。
當我重構為使用CacheLoader.load樣式語法時,我的緩存停止工作。 現在每個get()都是一個高速緩存未命中的對象,並開始調用load()。
我是否錯過了一些非常簡單的事情?
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]);
Key
類必須正確實現equals()
和hashcode()
。
您可以使用Guava EqualsTester來測試您的equals和hashCode:
看來您的Key
類需要定義一個equals()
方法。
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