001/*-
002 * #%L
003 * HAPI FHIR - Server Framework
004 * %%
005 * Copyright (C) 2014 - 2025 Smile CDR, Inc.
006 * %%
007 * Licensed under the Apache License, Version 2.0 (the "License");
008 * you may not use this file except in compliance with the License.
009 * You may obtain a copy of the License at
010 *
011 *      http://www.apache.org/licenses/LICENSE-2.0
012 *
013 * Unless required by applicable law or agreed to in writing, software
014 * distributed under the License is distributed on an "AS IS" BASIS,
015 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
016 * See the License for the specific language governing permissions and
017 * limitations under the License.
018 * #L%
019 */
020package ca.uhn.fhir.rest.server.messaging;
021
022import ca.uhn.fhir.rest.server.messaging.json.BaseJsonMessage;
023import jakarta.annotation.Nonnull;
024
025import java.util.Map;
026import java.util.Optional;
027import java.util.UUID;
028
029/**
030 * This interface is implemented by serializable "wrapper" message classes that are exchanged with Massage Brokers. HAPI-FHIR
031 * message classes implement both {@link org.springframework.messaging.Message} and {@link IMessage} so that they can
032 * be exchanged with both JMS and non-JMS brokers. These message wrappers wrap a serializable payload that is the main content
033 * of the message. This wrapper also contains meta-data about the message such as headers and a message key. The message key
034 * is used by non-JMS brokers for partition selection.
035 *
036 * @param <T> the type of the message payload. In most cases, T will be a subclass of {@link BaseJsonMessage}
037 */
038public interface IMessage<T> {
039        /**
040         * The message key is used by brokers that support channel partitioning. The message key is used to determine which partition
041         * a message is stored on. If message order is important, then the same message key should be used for all messages that need
042         * to preserve their order. E.g. if a series of messages create, update, and delete a resource, the resource id would be a good
043         * candidate for the message key to ensure the order of operations is preserved on all messages concerning that resource.
044         * @return the key of the message.
045         */
046        @Nonnull
047        default String getMessageKey() {
048                return UUID.randomUUID().toString();
049        }
050
051        /**
052         * @return a map of message headers
053         */
054        @Nonnull
055        Map<String, Object> getHeaders();
056
057        /**
058         * @return a header value as an Optional
059         */
060        default <H> Optional<H> getHeader(String theHeaderName) {
061                return (Optional<H>) Optional.ofNullable(getHeaders().get(theHeaderName));
062        }
063
064        /**
065         * @return the de-serialized value of the message
066         */
067        T getPayload();
068}