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);
 	}

spring-messaging/src/test/kotlin/org/springframework/messaging/converter/KotlinSerializationJsonMessageConverterTests.kt

@@ -0,0 +1,214 @@
+/*
+ * Copyright 2002-2019 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 kotlinx.serialization.Serializable
+import org.assertj.core.api.Assertions
+import org.junit.jupiter.api.Test
+import org.springframework.core.MethodParameter
+import org.springframework.messaging.support.MessageBuilder
+import java.nio.charset.StandardCharsets
+import kotlin.reflect.typeOf
+
+@Suppress("UsePropertyAccessSyntax")
+class KotlinSerializationJsonMessageConverterTests {
+
+	private val converter = KotlinSerializationJsonMessageConverter()
+
+	@Test
+	fun readObject() {
+		val payload = """
+			{
+				"bytes": [
+					1,
+					2
+				],
+				"array": [
+					"Foo",
+					"Bar"
+				],
+				"number": 42,
+				"string": "Foo",
+				"bool": true,
+				"fraction": 42
+			}
+		""".trimIndent()
+		val message = MessageBuilder.withPayload(payload.toByteArray(StandardCharsets.UTF_8)).build()
+		val result = converter.fromMessage(message, SerializableBean::class.java) as SerializableBean
+
+		Assertions.assertThat(result.bytes).containsExactly(0x1, 0x2)
+		Assertions.assertThat(result.array).containsExactly("Foo", "Bar")
+		Assertions.assertThat(result.number).isEqualTo(42)
+		Assertions.assertThat(result.string).isEqualTo("Foo")
+		Assertions.assertThat(result.bool).isTrue()
+		Assertions.assertThat(result.fraction).isEqualTo(42.0f)
+	}
+
+	@Test
+	@Suppress("UNCHECKED_CAST")
+	fun readArrayOfObjects() {
+		val payload = """
+			[
+				{
+					"bytes": [
+						1,
+						2
+					],
+					"array": [
+						"Foo",
+						"Bar"
+					],
+					"number": 42,
+					"string": "Foo",
+					"bool": true,
+					"fraction": 42
+				}
+			]
+		""".trimIndent()
+		val message = MessageBuilder.withPayload(payload.toByteArray(StandardCharsets.UTF_8)).build()
+		val result = converter.fromMessage(message, Array<SerializableBean>::class.java) as Array<SerializableBean>
+
+		Assertions.assertThat(result).hasSize(1)
+		Assertions.assertThat(result[0].bytes).containsExactly(0x1, 0x2)
+		Assertions.assertThat(result[0].array).containsExactly("Foo", "Bar")
+		Assertions.assertThat(result[0].number).isEqualTo(42)
+		Assertions.assertThat(result[0].string).isEqualTo("Foo")
+		Assertions.assertThat(result[0].bool).isTrue()
+		Assertions.assertThat(result[0].fraction).isEqualTo(42.0f)
+	}
+
+	@Test
+	@Suppress("UNCHECKED_CAST")
+	@ExperimentalStdlibApi
+	fun readGenericCollection() {
+		val payload = """
+			[
+				{
+					"bytes": [
+						1,
+						2
+					],
+					"array": [
+						"Foo",
+						"Bar"
+					],
+					"number": 42,
+					"string": "Foo",
+					"bool": true,
+					"fraction": 42
+				}
+			]
+		""".trimIndent()
+		val method = javaClass.getDeclaredMethod("handleList", List::class.java)
+		val param = MethodParameter(method, 0)
+		val message = MessageBuilder.withPayload(payload.toByteArray(StandardCharsets.UTF_8)).build()
+		val result = converter.fromMessage(message, typeOf<List<SerializableBean>>()::class.java, param) as List<SerializableBean>
+
+		Assertions.assertThat(result).hasSize(1)
+		Assertions.assertThat(result[0].bytes).containsExactly(0x1, 0x2)
+		Assertions.assertThat(result[0].array).containsExactly("Foo", "Bar")
+		Assertions.assertThat(result[0].number).isEqualTo(42)
+		Assertions.assertThat(result[0].string).isEqualTo("Foo")
+		Assertions.assertThat(result[0].bool).isTrue()
+		Assertions.assertThat(result[0].fraction).isEqualTo(42.0f)
+	}
+
+	@Test
+	fun readFailsOnInvalidJson() {
+		val payload = """
+			this is an invalid JSON document
+		""".trimIndent()
+
+		val message = MessageBuilder.withPayload(payload.toByteArray(StandardCharsets.UTF_8)).build()
+		Assertions.assertThatExceptionOfType(MessageConversionException::class.java).isThrownBy {
+			converter.fromMessage(message, SerializableBean::class.java)
+		}
+	}
+
+	@Test
+	fun writeObject() {
+		val serializableBean = SerializableBean(byteArrayOf(0x1, 0x2), arrayOf("Foo", "Bar"), 42, "Foo", true, 42.0f)
+		val message = converter.toMessage(serializableBean, null)
+		val result = String((message!!.payload as ByteArray), StandardCharsets.UTF_8)
+
+		Assertions.assertThat(result)
+				.contains("\"bytes\":[1,2]")
+				.contains("\"array\":[\"Foo\",\"Bar\"]")
+				.contains("\"number\":42")
+				.contains("\"string\":\"Foo\"")
+				.contains("\"bool\":true")
+				.contains("\"fraction\":42.0")
+	}
+
+	@Test
+	fun writeObjectWithNullableProperty() {
+		val serializableBean = SerializableBean(byteArrayOf(0x1, 0x2), arrayOf("Foo", "Bar"), 42, null, true, 42.0f)
+		val message = converter.toMessage(serializableBean, null)
+		val result = String((message!!.payload as ByteArray), StandardCharsets.UTF_8)
+
+		Assertions.assertThat(result)
+				.contains("\"bytes\":[1,2]")
+				.contains("\"array\":[\"Foo\",\"Bar\"]")
+				.contains("\"number\":42")
+				.contains("\"string\":null")
+				.contains("\"bool\":true")
+				.contains("\"fraction\":42.0")
+	}
+
+	@Test
+	fun writeArrayOfObjects() {
+		val serializableBean = SerializableBean(byteArrayOf(0x1, 0x2), arrayOf("Foo", "Bar"), 42, "Foo", true, 42.0f)
+		val expectedJson = """
+			[{"bytes":[1,2],"array":["Foo","Bar"],"number":42,"string":"Foo","bool":true,"fraction":42.0}]
+		""".trimIndent()
+
+		val message = converter.toMessage(arrayOf(serializableBean), null)
+		val result = String((message!!.payload as ByteArray), StandardCharsets.UTF_8)
+
+		Assertions.assertThat(result).isEqualTo(expectedJson)
+	}
+
+	@Test
+	@ExperimentalStdlibApi
+	fun writeGenericCollection() {
+		val serializableBean = SerializableBean(byteArrayOf(0x1, 0x2), arrayOf("Foo", "Bar"), 42, "Foo", true, 42.0f)
+		val expectedJson = """
+			[{"bytes":[1,2],"array":["Foo","Bar"],"number":42,"string":"Foo","bool":true,"fraction":42.0}]
+		""".trimIndent()
+
+		val method = javaClass.getDeclaredMethod("handleList", List::class.java)
+		val param = MethodParameter(method, 0)
+		val message = converter.toMessage(arrayListOf(serializableBean), null, param)
+		val result = String((message!!.payload as ByteArray), StandardCharsets.UTF_8)
+
+		Assertions.assertThat(result).isEqualTo(expectedJson)
+	}
+
+	@Suppress("UNUSED_PARAMETER")
+	fun handleList(payload: List<SerializableBean>) {}
+
+	@Serializable
+	@Suppress("ArrayInDataClass")
+	data class SerializableBean(
+			val bytes: ByteArray,
+			val array: Array<String>,
+			val number: Int,
+			val string: String?,
+			val bool: Boolean,
+			val fraction: Float
+	)
+}