com.google.common.cache.CacheLoader#from ( )源码实例Demo

private static CacheLoader<Pair<Class<RelNode>, Class<Metadata>>,
    UnboundMetadata<Metadata>> loader(final RelMetadataProvider provider) {
  return CacheLoader.from(key -> {
    final UnboundMetadata<Metadata> function =
        provider.apply(key.left, key.right);
    // Return DUMMY, not null, so the cache knows to not ask again.
    return function != null ? function : DUMMY;
  });
}
 

private static CacheLoader<Pair<Class<RelNode>, Class<Metadata>>,
    UnboundMetadata<Metadata>> loader(final RelMetadataProvider provider) {
  return CacheLoader.from(key -> {
    final UnboundMetadata<Metadata> function =
        provider.apply(key.left, key.right);
    // Return DUMMY, not null, so the cache knows to not ask again.
    return function != null ? function : DUMMY;
  });
}
 

public CachedSpecService(CoreSpecService coreService, StoreProto.Store store) {
  this.coreService = coreService;
  this.store = coreService.registerStore(store);

  Map<String, FeatureSetSpec> featureSets = getFeatureSetMap();
  featureToFeatureSetMapping =
      new ConcurrentHashMap<>(getFeatureToFeatureSetMapping(featureSets));
  CacheLoader<String, FeatureSetSpec> featureSetCacheLoader = CacheLoader.from(featureSets::get);
  featureSetCache =
      CacheBuilder.newBuilder().maximumSize(MAX_SPEC_COUNT).build(featureSetCacheLoader);
  featureSetCache.putAll(featureSets);
}
 

private LoadingCache<UnorderedPair<T>, Double> createCache() {
	CacheLoader<UnorderedPair<T>, Double> loader = CacheLoader
		.from(similarityMeasure::calculateSimilarity);
	return CacheBuilder.newBuilder()
		.maximumSize(maximumSize)
		.build(loader);
}
 

private static CacheLoader<Pair<Class<RelNode>, Class<Metadata>>,
    UnboundMetadata<Metadata>> loader(final RelMetadataProvider provider) {
  return CacheLoader.from(key -> {
    final UnboundMetadata<Metadata> function =
        provider.apply(key.left, key.right);
    // Return DUMMY, not null, so the cache knows to not ask again.
    return function != null ? function : DUMMY;
  });
}
 

private LoadingCache<GreaterOrEqualCall, IntCollection> createCache() {
	CacheLoader<GreaterOrEqualCall, IntCollection> loader = CacheLoader
		.from(GreaterOrEqualCall::call);
	return CACHE_BUILDER.build(loader);
}