ContextAwareServiceCollectionResolverImpl.java

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package io.wcm.sling.commons.caservice.impl;

import java.util.Collection;
import java.util.concurrent.TimeUnit;
import java.util.function.BiFunction;
import java.util.stream.Stream;

import org.apache.sling.api.adapter.Adaptable;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.github.benmanes.caffeine.cache.Caffeine;
import com.github.benmanes.caffeine.cache.LoadingCache;
import com.github.benmanes.caffeine.cache.RemovalCause;

import io.wcm.sling.commons.caservice.ContextAwareService;
import io.wcm.sling.commons.caservice.ContextAwareServiceCollectionResolver;

class ContextAwareServiceCollectionResolverImpl<S extends ContextAwareService, D>
    implements ContextAwareServiceCollectionResolver<S, D> {

  private final Collection<ServiceReference<S>> serviceReferenceCollection;
  private final ResourcePathResolver resourcePathResolver;

  // cache of service trackers for each SPI interface
  private final LoadingCache<ServiceReference<S>, CollectionItemDecoration<S, D>> decorationCache;

  private static final Logger log = LoggerFactory.getLogger(ContextAwareServiceCollectionResolverImpl.class);

  ContextAwareServiceCollectionResolverImpl(@NotNull Collection<ServiceReference<S>> serviceReferenceCollection,
      @NotNull BiFunction<@NotNull ServiceReference<S>, @Nullable S, @Nullable D> decorator,
      @NotNull ResourcePathResolver resourcePathResolver,
      @NotNull BundleContext bundleContext) {
    this.serviceReferenceCollection = serviceReferenceCollection;
    this.resourcePathResolver = resourcePathResolver;
    this.decorationCache = buildCache(decorator, bundleContext);
  }

  private static <S extends ContextAwareService, D> LoadingCache<ServiceReference<S>, CollectionItemDecoration<S, D>> buildCache(
      @NotNull BiFunction<@NotNull ServiceReference<S>, @Nullable S, @Nullable D> decorator, @NotNull BundleContext bundleContext) {
    return Caffeine.newBuilder()
        // expire cached entry after 24h
        .expireAfterAccess(24, TimeUnit.HOURS)
        // unget service on removal
        .removalListener((ServiceReference<S> key, CollectionItemDecoration<S, D> value, RemovalCause cause) -> {
          log.debug("Remove service {}", value);
          bundleContext.ungetService(key);
        })
        // build cache lazily
        .build((ServiceReference<S> serviceReference) -> {
          CollectionItemDecoration<S, D> item = new CollectionItemDecoration<>(serviceReference, decorator, bundleContext);
          log.debug("Add service {}", item);
          return item;
        });
  }

  @Override
  public @Nullable S resolve(@Nullable Adaptable adaptable) {
    return getMatching(adaptable)
        .map(CollectionItemDecoration::getService)
        .findFirst().orElse(null);
  }

  @Override
  @SuppressWarnings("null")
  public @NotNull Stream<S> resolveAll(@Nullable Adaptable adaptable) {
    return getMatching(adaptable)
        .map(CollectionItemDecoration::getService);
  }

  @Override
  public @Nullable D resolveDecorated(@Nullable Adaptable adaptable) {
    return getMatching(adaptable)
        .map(CollectionItemDecoration::getDecoration)
        .findFirst().orElse(null);
  }

  @Override
  @SuppressWarnings("null")
  public @NotNull Stream<D> resolveAllDecorated(@Nullable Adaptable adaptable) {
    return getMatching(adaptable)
        .map(CollectionItemDecoration::getDecoration);
  }

  private @NotNull Stream<CollectionItemDecoration<S, D>> getMatching(@Nullable Adaptable adaptable) {
    String resourcePath = resourcePathResolver.get(adaptable);
    return serviceReferenceCollection.stream()
        .map(decorationCache::get)
        .filter(CollectionItemDecoration::isValid)
        .filter(item -> item.matches(resourcePath));
  }

  @Override
  public void close() {
    this.decorationCache.invalidateAll();
  }

}