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  package org.apache.cayenne.cache.invalidation;
  
  import org.apache.cayenne.Persistent;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.function.Function;
  
  /**
   * @since 4.0
   */
  public class CacheGroupsHandler implements InvalidationHandler {
  
      public CacheGroupsHandler() {
      }
  
      /**
       * Return invalidation function that returns values
       * of {@link CacheGroups} and {@link CacheGroup} annotations for the given type.
       */
      @Override
      public Function<Persistent, Collection<CacheGroupDescriptor>> canHandle(Class<? extends Persistent> type) {
  
          CacheGroup multipleCacheGroups = type.getAnnotation(CacheGroup.class);
          CacheGroups cacheGroups = type.getAnnotation(CacheGroups.class);
          if (cacheGroups == null && multipleCacheGroups == null) {
              return null;
          }
  
          final Collection<CacheGroupDescriptor> groupsList = new ArrayList<>();
          extractCacheGroups(cacheGroups, groupsList);
          extractCacheGroups(multipleCacheGroups, groupsList);
  
          return p -> groupsList;
      }
  
      private void extractCacheGroups(CacheGroup cacheGroup, Collection<CacheGroupDescriptor> groupsList) {
          if(cacheGroup == null) {
              return;
          }
          groupsList.add(new CacheGroupDescriptor(cacheGroup.value(), cacheGroup.keyType(), cacheGroup.valueType()));
      }
  
      private void extractCacheGroups(CacheGroups cacheGroups, Collection<CacheGroupDescriptor> groupsList) {
          if(cacheGroups == null) {
              return;
          }
  
          for(String name : cacheGroups.value()) {
              groupsList.add(new CacheGroupDescriptor(name));
          }
  
          for(CacheGroup group : cacheGroups.groups()) {
              extractCacheGroups(group, groupsList);
          }
      }
  }
  