Add kotlinx.serialization JSON support to Spring Messaging

Closes gh-25883

spring-messaging/src/main/java/org/springframework/messaging/converter/KotlinSerializationJsonMessageConverter.java

@@ -0,0 +1,109 @@
+/*
+ * Copyright 2002-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.messaging.converter;
+
+import java.io.IOException;
+import java.io.Reader;
+import java.io.Writer;
+import java.lang.reflect.Type;
+import java.util.Map;
+
+import kotlinx.serialization.KSerializer;
+import kotlinx.serialization.SerializersKt;
+import kotlinx.serialization.json.Json;
+
+import org.springframework.util.ConcurrentReferenceHashMap;
+import org.springframework.util.FileCopyUtils;
+
+/**
+ * Implementation of {@link MessageConverter} that can read and write JSON
+ * using <a href="https://github.com/Kotlin/kotlinx.serialization">kotlinx.serialization</a>.
+ *
+ * <p>This converter can be used to bind {@code @Serializable} Kotlin classes.
+ *
+ * @author Sebastien Deleuze
+ * @since 5.3
+ */
+public class KotlinSerializationJsonMessageConverter extends AbstractJsonMessageConverter {
+
+	private static final Map<Type, KSerializer<Object>> serializerCache = new ConcurrentReferenceHashMap<>();
+
+	private final Json json;
+
+
+	/**
+	 * Construct a new {@code KotlinSerializationJsonMessageConverter} with default configuration.
+	 */
+	public KotlinSerializationJsonMessageConverter() {
+		this(Json.Default);
+	}
+
+	/**
+	 * Construct a new {@code KotlinSerializationJsonMessageConverter} with the given delegate.
+	 * @param json the Json instance to use
+	 */
+	public KotlinSerializationJsonMessageConverter(Json json) {
+		this.json = json;
+	}
+
+	@Override
+	protected Object fromJson(Reader reader, Type resolvedType) {
+		try {
+			return fromJson(FileCopyUtils.copyToString(reader), resolvedType);
+		}
+		catch (IOException ex) {
+			throw new MessageConversionException("Could not read JSON: " + ex.getMessage(), ex);
+		}
+	}
+
+	@Override
+	protected Object fromJson(String payload, Type resolvedType) {
+		return this.json.decodeFromString(serializer(resolvedType), payload);
+	}
+
+	@Override
+	protected void toJson(Object payload, Type resolvedType, Writer writer) {
+		try {
+			writer.write(toJson(payload, resolvedType).toCharArray());
+		}
+		catch (IOException ex) {
+			throw new MessageConversionException("Could not write JSON: " + ex.getMessage(), ex);
+		}
+	}
+
+	@Override
+	protected String toJson(Object payload, Type resolvedType) {
+		return this.json.encodeToString(serializer(resolvedType), payload);
+	}
+
+	/**
+	 * Tries to find a serializer that can marshall or unmarshall instances of the given type
+	 * using kotlinx.serialization. If no serializer can be found, an exception is thrown.
+	 * <p>Resolved serializers are cached and cached results are returned on successive calls.
+	 * @param type the type to find a serializer for
+	 * @return a resolved serializer for the given type
+	 * @throws RuntimeException if no serializer supporting the given type can be found
+	 */
+	private KSerializer<Object> serializer(Type type) {
+		KSerializer<Object> serializer = serializerCache.get(type);
+		if (serializer == null) {
+			serializer = SerializersKt.serializer(type);
+			serializerCache.put(type, serializer);
+		}
+		return serializer;
+	}
+}

spring-messaging/src/main/java/org/springframework/messaging/simp/config/AbstractMessageBrokerConfiguration.java

@@ -36,6 +36,7 @@ import org.springframework.messaging.converter.CompositeMessageConverter;
 import org.springframework.messaging.converter.DefaultContentTypeResolver;
 import org.springframework.messaging.converter.GsonMessageConverter;
 import org.springframework.messaging.converter.JsonbMessageConverter;
+import org.springframework.messaging.converter.KotlinSerializationJsonMessageConverter;
 import org.springframework.messaging.converter.MappingJackson2MessageConverter;
 import org.springframework.messaging.converter.MessageConverter;
 import org.springframework.messaging.converter.StringMessageConverter;
@@ -101,6 +102,8 @@ public abstract class AbstractMessageBrokerConfiguration implements ApplicationC
 
 	private static final boolean jsonbPresent;
 
+	private static final boolean kotlinSerializationJsonPresent;
+
 
 	static {
 		ClassLoader classLoader = AbstractMessageBrokerConfiguration.class.getClassLoader();
@@ -108,6 +111,7 @@ public abstract class AbstractMessageBrokerConfiguration implements ApplicationC
 				ClassUtils.isPresent("com.fasterxml.jackson.core.JsonGenerator", classLoader);
 		gsonPresent = ClassUtils.isPresent("com.google.gson.Gson", classLoader);
 		jsonbPresent = ClassUtils.isPresent("javax.json.bind.Jsonb", classLoader);
+		kotlinSerializationJsonPresent = ClassUtils.isPresent("kotlinx.serialization.json.Json", classLoader);
 	}
 
 
@@ -411,6 +415,9 @@ public abstract class AbstractMessageBrokerConfiguration implements ApplicationC
 			else if (jsonbPresent) {
 				converters.add(new JsonbMessageConverter());
 			}
+			else if (kotlinSerializationJsonPresent) {
+				converters.add(new KotlinSerializationJsonMessageConverter());
+			}
 		}
 		return new CompositeMessageConverter(converters);
 	}