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;
028import java.util.stream.Collectors;
029
030/**
031 * This interface is implemented by serializable "wrapper" message classes that are exchanged with Massage Brokers. HAPI-FHIR
032 * message classes implement both {@link org.springframework.messaging.Message} and {@link IMessage} so that they can
033 * be exchanged with both JMS and non-JMS brokers. These message wrappers wrap a serializable payload that is the main content
034 * of the message. This wrapper also contains meta-data about the message such as headers and a message key. The message key
035 * is used by non-JMS brokers for partition selection.
036 *
037 * @param <T> the type of the message payload. In most cases, T will be a subclass of {@link BaseJsonMessage}
038 */
039public interface IMessage<T> {
040        /**
041         * The message key is used by brokers that support channel partitioning. The message key is used to determine which partition
042         * a message is stored on. If message order is important, then the same message key should be used for all messages that need
043         * to preserve their order. E.g. if a series of messages create, update, and delete a resource, the resource id would be a good
044         * candidate for the message key to ensure the order of operations is preserved on all messages concerning that resource.
045         * @return the key of the message.
046         */
047        @Nonnull
048        default String getMessageKey() {
049                return UUID.randomUUID().toString();
050        }
051
052        /**
053         * @return a map of message headers
054         */
055        @Nonnull
056        Map<String, Object> getHeaders();
057
058        /**
059         * @return a header value as an Optional
060         */
061        default <H> Optional<H> getHeader(String theHeaderName) {
062                return (Optional<H>) Optional.ofNullable(getHeaders().get(theHeaderName));
063        }
064
065        /**
066         * @return the de-serialized value of the message
067         */
068        T getPayload();
069
070        /**
071         * @return headers as a String to String map where all values are replaced with their toString() value
072         */
073        default Map<String, String> getHeadersAsStrings() {
074                return convertHeaderValuesToStrings(getHeaders());
075        }
076
077        /**
078         * Converts a map of headers with Object values to a map with String values.
079         * This utility method converts all header values to their string representation using toString().
080         *
081         * @param theHeaders the headers map with Object values to convert
082         * @return a new map with the same keys but all values converted to strings
083         */
084        static Map<String, String> convertHeaderValuesToStrings(Map<String, Object> theHeaders) {
085                return theHeaders.entrySet().stream()
086                                .collect(Collectors.toMap(Map.Entry::getKey, e -> e.getValue().toString()));
087        }
088}