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  package org.apache.cayenne.crypto.transformer.value;
  
  import org.apache.cayenne.di.Inject;
  import org.apache.cayenne.di.Provider;
  import org.apache.cayenne.map.DbAttribute;
  
  /**
   * A {@link ValueTransformerFactory} that  allows to defer its initialization and hence allows Cayenne stack
   * to operate without cryto keys over a subset of entities that do not require encryption. Useful e.g. when the
   * crypto keys are supplied at a later point after startup.
   *
   * @since 4.0
   */
  public class LazyValueTransformerFactory implements ValueTransformerFactory {
  
      private Provider<ValueTransformerFactory> delegateProvider;
      private volatile ValueTransformerFactory delegate;
  
      public LazyValueTransformerFactory(@Inject Provider<ValueTransformerFactory> delegateProvider) {
          this.delegateProvider = delegateProvider;
      }
  
      @Override
      public ValueEncryptor encryptor(DbAttribute a) {
          return ensureInit().encryptor(a);
      }
  
      @Override
      public ValueDecryptor decryptor(DbAttribute a) {
          return ensureInit().decryptor(a);
      }
  
      protected ValueTransformerFactory ensureInit() {
  
          if (delegate == null) {
              synchronized (this) {
                  if (delegate == null) {
                      delegate = delegateProvider.get();
                  }
              }
          }
  
          return delegate;
      }
  
  }
  