MetadataNotificationListener.java

package org.springframework.roo.metadata;

/**
 * Indicates an implementation is able to process metadata notifications.
 * 
 * @author Ben Alex
 * @since 1.0
 */
public interface MetadataNotificationListener {

  /**
   * Invoked to notify an implementation that a particular source metadata
   * identification has requested to notify a particular destination metadata
   * identification of an event.
   * <p>
   * Both the source and destination metadata identifications can be either a
   * {@link MetadataIdentificationUtils#isIdentifyingClass(String)} or
   * {@link MetadataIdentificationUtils#isIdentifyingInstance(String)}.
   * However, both the source and metadata identifications must return true
   * when presented to {@link MetadataIdentificationUtils#isValid(String)}.
   * <p>
   * Where possible exceptions should not be thrown when processing metadata,
   * except for genuinely fatal operations. Simple failures to obtain metadata
   * information can be safely ignored and indicated via
   * {@link MetadataItem#isValid()}, with an expectation that metadata
   * depending on such metadata will call this method.
   * 
   * @param upstreamDependency the upstream source of the event (mandatory and
   *            must be valid)
   * @param downstreamDependency the downstream destination of the event (may
   *            be null if no particular downstream is targeted)
   */
  void notify(String upstreamDependency, String downstreamDependency);
}