Refine kotlinx.serialization support

This commit introduces the following changes:
 - Converters/codecs are now used based on generic type info.
 - On WebMvc and WebFlux, kotlinx.serialization is enabled along
   to Jackson because it only serializes Kotlin @Serializable classes
   which is not enough for error or actuator endpoints in Boot as
   described on spring-projects/spring-boot#24238.

TODO: leverage Kotlin/kotlinx.serialization#1164 when fixed.

Closes gh-26147

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

@@ -94,6 +94,7 @@ public class KotlinSerializationJsonMessageConverter extends AbstractJsonMessage
 	 * 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.
+	 * TODO Avoid relying on throwing exception when https://github.com/Kotlin/kotlinx.serialization/pull/1164 is fixed
 	 * @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

spring-web/src/main/java/org/springframework/http/codec/json/KotlinSerializationJsonDecoder.java

@@ -69,10 +69,38 @@ public class KotlinSerializationJsonDecoder extends AbstractDecoder<Object> {
 		this.json = json;
 	}
 
+	/**
+	 * Configure a limit on the number of bytes that can be buffered whenever
+	 * the input stream needs to be aggregated. This can be a result of
+	 * decoding to a single {@code DataBuffer},
+	 * {@link java.nio.ByteBuffer ByteBuffer}, {@code byte[]},
+	 * {@link org.springframework.core.io.Resource Resource}, {@code String}, etc.
+	 * It can also occur when splitting the input stream, e.g. delimited text,
+	 * in which case the limit applies to data buffered between delimiters.
+	 * <p>By default this is set to 256K.
+	 * @param byteCount the max number of bytes to buffer, or -1 for unlimited
+	 */
+	public void setMaxInMemorySize(int byteCount) {
+		this.stringDecoder.setMaxInMemorySize(byteCount);
+	}
+
+	/**
+	 * Return the {@link #setMaxInMemorySize configured} byte count limit.
+	 */
+	public int getMaxInMemorySize() {
+		return this.stringDecoder.getMaxInMemorySize();
+	}
+
 
 	@Override
 	public boolean canDecode(ResolvableType elementType, @Nullable MimeType mimeType) {
-		return (super.canDecode(elementType, mimeType) && !CharSequence.class.isAssignableFrom(elementType.toClass()));
+		try {
+			serializer(elementType.getType());
+			return (super.canDecode(elementType, mimeType) && !CharSequence.class.isAssignableFrom(elementType.toClass()));
+		}
+		catch (Exception ex) {
+			return false;
+		}
 	}
 
 	@Override
@@ -95,6 +123,7 @@ public class KotlinSerializationJsonDecoder extends AbstractDecoder<Object> {
 	 * 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.
+	 * TODO Avoid relying on throwing exception when https://github.com/Kotlin/kotlinx.serialization/pull/1164 is fixed
 	 * @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

spring-web/src/main/java/org/springframework/http/codec/json/KotlinSerializationJsonEncoder.java

@@ -71,8 +71,14 @@ public class KotlinSerializationJsonEncoder extends AbstractEncoder<Object> {
 
 	@Override
 	public boolean canEncode(ResolvableType elementType, @Nullable MimeType mimeType) {
-		return (super.canEncode(elementType, mimeType) && !String.class.isAssignableFrom(elementType.toClass()) &&
+		try {
-				!ServerSentEvent.class.isAssignableFrom(elementType.toClass()));
+			serializer(elementType.getType());
+			return (super.canEncode(elementType, mimeType) && !String.class.isAssignableFrom(elementType.toClass()) &&
+					!ServerSentEvent.class.isAssignableFrom(elementType.toClass()));
+		}
+		catch (Exception ex) {
+			return false;
+		}
 	}
 
 	@Override
@@ -105,6 +111,7 @@ public class KotlinSerializationJsonEncoder extends AbstractEncoder<Object> {
 	 * 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.
+	 * TODO Avoid relying on throwing exception when https://github.com/Kotlin/kotlinx.serialization/pull/1164 is fixed
 	 * @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

spring-web/src/main/java/org/springframework/http/codec/support/BaseDefaultCodecs.java

@@ -312,6 +312,11 @@ class BaseDefaultCodecs implements CodecConfigurer.DefaultCodecs, CodecConfigure
 					((ProtobufDecoder) codec).setMaxMessageSize(size);
 				}
 			}
+			if (kotlinSerializationJsonPresent) {
+				if (codec instanceof KotlinSerializationJsonDecoder) {
+					((KotlinSerializationJsonDecoder) codec).setMaxInMemorySize(size);
+				}
+			}
 			if (jackson2Present) {
 				if (codec instanceof AbstractJackson2Decoder) {
 					((AbstractJackson2Decoder) codec).setMaxInMemorySize(size);
@@ -385,12 +390,12 @@ class BaseDefaultCodecs implements CodecConfigurer.DefaultCodecs, CodecConfigure
 			return Collections.emptyList();
 		}
 		List<HttpMessageReader<?>> readers = new ArrayList<>();
+		if (kotlinSerializationJsonPresent) {
+			addCodec(readers, new DecoderHttpMessageReader<>(getKotlinSerializationJsonDecoder()));
+		}
 		if (jackson2Present) {
 			addCodec(readers, new DecoderHttpMessageReader<>(getJackson2JsonDecoder()));
 		}
-		else if (kotlinSerializationJsonPresent) {
-			addCodec(readers, new DecoderHttpMessageReader<>(getKotlinSerializationJsonDecoder()));
-		}
 		if (jackson2SmilePresent) {
 			addCodec(readers, new DecoderHttpMessageReader<>(this.jackson2SmileDecoder != null ?
 					(Jackson2SmileDecoder) this.jackson2SmileDecoder : new Jackson2SmileDecoder()));
@@ -484,12 +489,12 @@ class BaseDefaultCodecs implements CodecConfigurer.DefaultCodecs, CodecConfigure
 	 */
 	final List<HttpMessageWriter<?>> getBaseObjectWriters() {
 		List<HttpMessageWriter<?>> writers = new ArrayList<>();
+		if (kotlinSerializationJsonPresent) {
+			writers.add(new EncoderHttpMessageWriter<>(getKotlinSerializationJsonEncoder()));
+		}
 		if (jackson2Present) {
 			writers.add(new EncoderHttpMessageWriter<>(getJackson2JsonEncoder()));
 		}
-		else if (kotlinSerializationJsonPresent) {
-			writers.add(new EncoderHttpMessageWriter<>(getKotlinSerializationJsonEncoder()));
-		}
 		if (jackson2SmilePresent) {
 			writers.add(new EncoderHttpMessageWriter<>(this.jackson2SmileEncoder != null ?
 					(Jackson2SmileEncoder) this.jackson2SmileEncoder : new Jackson2SmileEncoder()));

spring-web/src/main/java/org/springframework/http/converter/json/KotlinSerializationJsonHttpMessageConverter.java

@@ -88,6 +88,28 @@ public class KotlinSerializationJsonHttpMessageConverter extends AbstractGeneric
 		}
 	}
 
+	@Override
+	public boolean canRead(Type type, @Nullable Class<?> contextClass, @Nullable MediaType mediaType) {
+		try {
+			serializer(GenericTypeResolver.resolveType(type, contextClass));
+			return canRead(mediaType);
+		}
+		catch (Exception ex) {
+			return false;
+		}
+	}
+
+	@Override
+	public boolean canWrite(@Nullable Type type, @Nullable Class<?> clazz, @Nullable MediaType mediaType) {
+		try {
+			serializer(GenericTypeResolver.resolveType(type, clazz));
+			return canWrite(mediaType);
+		}
+		catch (Exception ex) {
+			return false;
+		}
+	}
+
 	@Override
 	public final Object read(Type type, @Nullable Class<?> contextClass, HttpInputMessage inputMessage)
 			throws IOException, HttpMessageNotReadableException {
@@ -151,6 +173,7 @@ public class KotlinSerializationJsonHttpMessageConverter extends AbstractGeneric
 	 * 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.
+	 * TODO Avoid relying on throwing exception when https://github.com/Kotlin/kotlinx.serialization/pull/1164 is fixed
 	 * @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

spring-web/src/test/java/org/springframework/http/codec/support/ClientCodecConfigurerTests.java

@@ -56,6 +56,8 @@ import org.springframework.http.codec.json.Jackson2JsonDecoder;
 import org.springframework.http.codec.json.Jackson2JsonEncoder;
 import org.springframework.http.codec.json.Jackson2SmileDecoder;
 import org.springframework.http.codec.json.Jackson2SmileEncoder;
+import org.springframework.http.codec.json.KotlinSerializationJsonDecoder;
+import org.springframework.http.codec.json.KotlinSerializationJsonEncoder;
 import org.springframework.http.codec.multipart.MultipartHttpMessageWriter;
 import org.springframework.http.codec.protobuf.ProtobufDecoder;
 import org.springframework.http.codec.protobuf.ProtobufHttpMessageWriter;
@@ -81,7 +83,7 @@ public class ClientCodecConfigurerTests {
 	@Test
 	public void defaultReaders() {
 		List<HttpMessageReader<?>> readers = this.configurer.getReaders();
-		assertThat(readers.size()).isEqualTo(13);
+		assertThat(readers.size()).isEqualTo(14);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(ByteArrayDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(ByteBufferDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(DataBufferDecoder.class);
@@ -91,6 +93,7 @@ public class ClientCodecConfigurerTests {
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(ProtobufDecoder.class);
 		// SPR-16804
 		assertThat(readers.get(this.index.getAndIncrement()).getClass()).isEqualTo(FormHttpMessageReader.class);
+		assertThat(getNextDecoder(readers).getClass()).isEqualTo(KotlinSerializationJsonDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(Jackson2JsonDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(Jackson2SmileDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(Jaxb2XmlDecoder.class);
@@ -101,7 +104,7 @@ public class ClientCodecConfigurerTests {
 	@Test
 	public void defaultWriters() {
 		List<HttpMessageWriter<?>> writers = this.configurer.getWriters();
-		assertThat(writers.size()).isEqualTo(12);
+		assertThat(writers.size()).isEqualTo(13);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(ByteArrayEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(ByteBufferEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(DataBufferEncoder.class);
@@ -110,6 +113,7 @@ public class ClientCodecConfigurerTests {
 		assertStringEncoder(getNextEncoder(writers), true);
 		assertThat(writers.get(index.getAndIncrement()).getClass()).isEqualTo(ProtobufHttpMessageWriter.class);
 		assertThat(writers.get(this.index.getAndIncrement()).getClass()).isEqualTo(MultipartHttpMessageWriter.class);
+		assertThat(getNextEncoder(writers).getClass()).isEqualTo(KotlinSerializationJsonEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(Jackson2JsonEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(Jackson2SmileEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(Jaxb2XmlEncoder.class);
@@ -130,7 +134,7 @@ public class ClientCodecConfigurerTests {
 		int size = 99;
 		this.configurer.defaultCodecs().maxInMemorySize(size);
 		List<HttpMessageReader<?>> readers = this.configurer.getReaders();
-		assertThat(readers.size()).isEqualTo(13);
+		assertThat(readers.size()).isEqualTo(14);
 		assertThat(((ByteArrayDecoder) getNextDecoder(readers)).getMaxInMemorySize()).isEqualTo(size);
 		assertThat(((ByteBufferDecoder) getNextDecoder(readers)).getMaxInMemorySize()).isEqualTo(size);
 		assertThat(((DataBufferDecoder) getNextDecoder(readers)).getMaxInMemorySize()).isEqualTo(size);
@@ -140,6 +144,7 @@ public class ClientCodecConfigurerTests {
 		assertThat(((ProtobufDecoder) getNextDecoder(readers)).getMaxMessageSize()).isEqualTo(size);
 		assertThat(((FormHttpMessageReader) nextReader(readers)).getMaxInMemorySize()).isEqualTo(size);
 
+		assertThat(((KotlinSerializationJsonDecoder) getNextDecoder(readers)).getMaxInMemorySize()).isEqualTo(size);
 		assertThat(((Jackson2JsonDecoder) getNextDecoder(readers)).getMaxInMemorySize()).isEqualTo(size);
 		assertThat(((Jackson2SmileDecoder) getNextDecoder(readers)).getMaxInMemorySize()).isEqualTo(size);
 		assertThat(((Jaxb2XmlDecoder) getNextDecoder(readers)).getMaxInMemorySize()).isEqualTo(size);
@@ -187,7 +192,7 @@ public class ClientCodecConfigurerTests {
 		writers = findCodec(this.configurer.getWriters(), MultipartHttpMessageWriter.class).getPartWriters();
 
 		assertThat(sseDecoder).isNotSameAs(jackson2Decoder);
-		assertThat(writers).hasSize(11);
+		assertThat(writers).hasSize(12);
 	}
 
 	@Test // gh-24194
@@ -197,7 +202,7 @@ public class ClientCodecConfigurerTests {
 		List<HttpMessageWriter<?>> writers =
 				findCodec(clone.getWriters(), MultipartHttpMessageWriter.class).getPartWriters();
 
-		assertThat(writers).hasSize(11);
+		assertThat(writers).hasSize(12);
 	}
 
 	@Test
@@ -211,7 +216,7 @@ public class ClientCodecConfigurerTests {
 		List<HttpMessageWriter<?>> writers =
 				findCodec(clone.getWriters(), MultipartHttpMessageWriter.class).getPartWriters();
 
-		assertThat(writers).hasSize(11);
+		assertThat(writers).hasSize(12);
 	}
 
 	private Decoder<?> getNextDecoder(List<HttpMessageReader<?>> readers) {

spring-web/src/test/java/org/springframework/http/codec/support/CodecConfigurerTests.java

@@ -52,6 +52,8 @@ import org.springframework.http.codec.json.Jackson2JsonDecoder;
 import org.springframework.http.codec.json.Jackson2JsonEncoder;
 import org.springframework.http.codec.json.Jackson2SmileDecoder;
 import org.springframework.http.codec.json.Jackson2SmileEncoder;
+import org.springframework.http.codec.json.KotlinSerializationJsonDecoder;
+import org.springframework.http.codec.json.KotlinSerializationJsonEncoder;
 import org.springframework.http.codec.protobuf.ProtobufDecoder;
 import org.springframework.http.codec.protobuf.ProtobufEncoder;
 import org.springframework.http.codec.protobuf.ProtobufHttpMessageWriter;
@@ -79,7 +81,7 @@ class CodecConfigurerTests {
 	@Test
 	void defaultReaders() {
 		List<HttpMessageReader<?>> readers = this.configurer.getReaders();
-		assertThat(readers.size()).isEqualTo(12);
+		assertThat(readers.size()).isEqualTo(13);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(ByteArrayDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(ByteBufferDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(DataBufferDecoder.class);
@@ -88,6 +90,7 @@ class CodecConfigurerTests {
 		assertStringDecoder(getNextDecoder(readers), true);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(ProtobufDecoder.class);
 		assertThat(readers.get(this.index.getAndIncrement()).getClass()).isEqualTo(FormHttpMessageReader.class);
+		assertThat(getNextDecoder(readers).getClass()).isEqualTo(KotlinSerializationJsonDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(Jackson2JsonDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(Jackson2SmileDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(Jaxb2XmlDecoder.class);
@@ -97,7 +100,7 @@ class CodecConfigurerTests {
 	@Test
 	void defaultWriters() {
 		List<HttpMessageWriter<?>> writers = this.configurer.getWriters();
-		assertThat(writers.size()).isEqualTo(11);
+		assertThat(writers.size()).isEqualTo(12);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(ByteArrayEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(ByteBufferEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(DataBufferEncoder.class);
@@ -105,6 +108,7 @@ class CodecConfigurerTests {
 		assertThat(writers.get(index.getAndIncrement()).getClass()).isEqualTo(ResourceHttpMessageWriter.class);
 		assertStringEncoder(getNextEncoder(writers), true);
 		assertThat(writers.get(index.getAndIncrement()).getClass()).isEqualTo(ProtobufHttpMessageWriter.class);
+		assertThat(getNextEncoder(writers).getClass()).isEqualTo(KotlinSerializationJsonEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(Jackson2JsonEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(Jackson2SmileEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(Jaxb2XmlEncoder.class);
@@ -133,7 +137,7 @@ class CodecConfigurerTests {
 
 		List<HttpMessageReader<?>> readers = this.configurer.getReaders();
 
-		assertThat(readers.size()).isEqualTo(16);
+		assertThat(readers.size()).isEqualTo(17);
 		assertThat(getNextDecoder(readers)).isSameAs(customDecoder1);
 		assertThat(readers.get(this.index.getAndIncrement())).isSameAs(customReader1);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(ByteArrayDecoder.class);
@@ -146,6 +150,7 @@ class CodecConfigurerTests {
 		assertThat(readers.get(this.index.getAndIncrement()).getClass()).isEqualTo(FormHttpMessageReader.class);
 		assertThat(getNextDecoder(readers)).isSameAs(customDecoder2);
 		assertThat(readers.get(this.index.getAndIncrement())).isSameAs(customReader2);
+		assertThat(getNextDecoder(readers).getClass()).isEqualTo(KotlinSerializationJsonDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(Jackson2JsonDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(Jackson2SmileDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(Jaxb2XmlDecoder.class);
@@ -174,7 +179,7 @@ class CodecConfigurerTests {
 
 		List<HttpMessageWriter<?>> writers = this.configurer.getWriters();
 
-		assertThat(writers.size()).isEqualTo(15);
+		assertThat(writers.size()).isEqualTo(16);
 		assertThat(getNextEncoder(writers)).isSameAs(customEncoder1);
 		assertThat(writers.get(this.index.getAndIncrement())).isSameAs(customWriter1);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(ByteArrayEncoder.class);
@@ -186,6 +191,7 @@ class CodecConfigurerTests {
 		assertThat(writers.get(index.getAndIncrement()).getClass()).isEqualTo(ProtobufHttpMessageWriter.class);
 		assertThat(getNextEncoder(writers)).isSameAs(customEncoder2);
 		assertThat(writers.get(this.index.getAndIncrement())).isSameAs(customWriter2);
+		assertThat(getNextEncoder(writers).getClass()).isEqualTo(KotlinSerializationJsonEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(Jackson2JsonEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(Jackson2SmileEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(Jaxb2XmlEncoder.class);

spring-web/src/test/java/org/springframework/http/codec/support/ServerCodecConfigurerTests.java

@@ -56,6 +56,8 @@ import org.springframework.http.codec.json.Jackson2JsonDecoder;
 import org.springframework.http.codec.json.Jackson2JsonEncoder;
 import org.springframework.http.codec.json.Jackson2SmileDecoder;
 import org.springframework.http.codec.json.Jackson2SmileEncoder;
+import org.springframework.http.codec.json.KotlinSerializationJsonDecoder;
+import org.springframework.http.codec.json.KotlinSerializationJsonEncoder;
 import org.springframework.http.codec.multipart.DefaultPartHttpMessageReader;
 import org.springframework.http.codec.multipart.MultipartHttpMessageReader;
 import org.springframework.http.codec.multipart.PartHttpMessageWriter;
@@ -83,7 +85,7 @@ public class ServerCodecConfigurerTests {
 	@Test
 	public void defaultReaders() {
 		List<HttpMessageReader<?>> readers = this.configurer.getReaders();
-		assertThat(readers.size()).isEqualTo(14);
+		assertThat(readers.size()).isEqualTo(15);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(ByteArrayDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(ByteBufferDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(DataBufferDecoder.class);
@@ -94,6 +96,7 @@ public class ServerCodecConfigurerTests {
 		assertThat(readers.get(this.index.getAndIncrement()).getClass()).isEqualTo(FormHttpMessageReader.class);
 		assertThat(readers.get(this.index.getAndIncrement()).getClass()).isEqualTo(DefaultPartHttpMessageReader.class);
 		assertThat(readers.get(this.index.getAndIncrement()).getClass()).isEqualTo(MultipartHttpMessageReader.class);
+		assertThat(getNextDecoder(readers).getClass()).isEqualTo(KotlinSerializationJsonDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(Jackson2JsonDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(Jackson2SmileDecoder.class);
 		assertThat(getNextDecoder(readers).getClass()).isEqualTo(Jaxb2XmlDecoder.class);
@@ -103,7 +106,7 @@ public class ServerCodecConfigurerTests {
 	@Test
 	public void defaultWriters() {
 		List<HttpMessageWriter<?>> writers = this.configurer.getWriters();
-		assertThat(writers.size()).isEqualTo(13);
+		assertThat(writers.size()).isEqualTo(14);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(ByteArrayEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(ByteBufferEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(DataBufferEncoder.class);
@@ -112,6 +115,7 @@ public class ServerCodecConfigurerTests {
 		assertStringEncoder(getNextEncoder(writers), true);
 		assertThat(writers.get(index.getAndIncrement()).getClass()).isEqualTo(ProtobufHttpMessageWriter.class);
 		assertThat(writers.get(this.index.getAndIncrement()).getClass()).isEqualTo(PartHttpMessageWriter.class);
+		assertThat(getNextEncoder(writers).getClass()).isEqualTo(KotlinSerializationJsonEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(Jackson2JsonEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(Jackson2SmileEncoder.class);
 		assertThat(getNextEncoder(writers).getClass()).isEqualTo(Jaxb2XmlEncoder.class);
@@ -152,6 +156,7 @@ public class ServerCodecConfigurerTests {
 		DefaultPartHttpMessageReader reader = (DefaultPartHttpMessageReader) multipartReader.getPartReader();
 		assertThat((reader).getMaxInMemorySize()).isEqualTo(size);
 
+		assertThat(((KotlinSerializationJsonDecoder) getNextDecoder(readers)).getMaxInMemorySize()).isEqualTo(size);
 		assertThat(((Jackson2JsonDecoder) getNextDecoder(readers)).getMaxInMemorySize()).isEqualTo(size);
 		assertThat(((Jackson2SmileDecoder) getNextDecoder(readers)).getMaxInMemorySize()).isEqualTo(size);
 		assertThat(((Jaxb2XmlDecoder) getNextDecoder(readers)).getMaxInMemorySize()).isEqualTo(size);

spring-web/src/test/kotlin/org/springframework/http/codec/json/KotlinSerializationJsonDecoderTests.kt

@@ -53,6 +53,11 @@ class KotlinSerializationJsonDecoderTests : AbstractDecoderTests<KotlinSerializa
 				MediaType("application", "json", StandardCharsets.US_ASCII))).isTrue()
 		Assertions.assertThat(decoder.canDecode(ResolvableType.forClass(Pojo::class.java),
 				MediaType("application", "json", StandardCharsets.ISO_8859_1))).isTrue()
+
+		Assertions.assertThat(decoder.canDecode(ResolvableType.forClassWithGenerics(List::class.java, Int::class.java), MediaType.APPLICATION_JSON)).isTrue()
+		Assertions.assertThat(decoder.canDecode(ResolvableType.forClassWithGenerics(List::class.java, Pojo::class.java), MediaType.APPLICATION_JSON)).isTrue()
+		Assertions.assertThat(decoder.canDecode(ResolvableType.forClassWithGenerics(ArrayList::class.java, Int::class.java), MediaType.APPLICATION_JSON)).isTrue()
+		Assertions.assertThat(decoder.canDecode(ResolvableType.forClassWithGenerics(ArrayList::class.java, Int::class.java), MediaType.APPLICATION_PDF)).isFalse()
 	}
 
 	@Test

spring-web/src/test/kotlin/org/springframework/http/codec/json/KotlinSerializationJsonEncoderTests.kt

@@ -49,7 +49,11 @@ class KotlinSerializationJsonEncoderTests : AbstractEncoderTests<KotlinSerializa
 				MediaType("application", "json", StandardCharsets.UTF_8))).isTrue()
 		Assertions.assertThat(encoder.canEncode(ResolvableType.forClass(Pojo::class.java),
 				MediaType("application", "json", StandardCharsets.US_ASCII))).isTrue()
-		Assertions.assertThat(encoder.canEncode(ResolvableType.NONE, null)).isTrue()
+
+		Assertions.assertThat(encoder.canEncode(ResolvableType.forClassWithGenerics(List::class.java, Int::class.java), MediaType.APPLICATION_JSON)).isTrue()
+		Assertions.assertThat(encoder.canEncode(ResolvableType.forClassWithGenerics(List::class.java, KotlinSerializationJsonDecoderTests.Pojo::class.java), MediaType.APPLICATION_JSON)).isTrue()
+		Assertions.assertThat(encoder.canEncode(ResolvableType.forClassWithGenerics(ArrayList::class.java, Int::class.java), MediaType.APPLICATION_JSON)).isTrue()
+		Assertions.assertThat(encoder.canEncode(ResolvableType.forClassWithGenerics(ArrayList::class.java, Int::class.java), MediaType.APPLICATION_PDF)).isFalse()
 	}
 
 	@Test

spring-web/src/test/kotlin/org/springframework/http/converter/json/KotlinSerializationJsonHttpMessageConverterTests.kt

@@ -24,6 +24,8 @@ import org.springframework.http.MediaType
 import org.springframework.http.MockHttpInputMessage
 import org.springframework.http.MockHttpOutputMessage
 import org.springframework.http.converter.HttpMessageNotReadableException
+import java.lang.reflect.ParameterizedType
+import java.lang.reflect.Type
 import java.nio.charset.StandardCharsets
 import kotlin.reflect.javaType
 import kotlin.reflect.typeOf
@@ -34,6 +36,7 @@ import kotlin.reflect.typeOf
  * @author Andreas Ahlenstorf
  * @author Sebastien Deleuze
  */
+@Suppress("UsePropertyAccessSyntax")
 class KotlinSerializationJsonHttpMessageConverterTests {
 
 	private val converter = KotlinSerializationJsonHttpMessageConverter()
@@ -48,6 +51,11 @@ class KotlinSerializationJsonHttpMessageConverterTests {
 		assertThat(converter.canRead(Map::class.java, MediaType.APPLICATION_JSON)).isTrue()
 		assertThat(converter.canRead(List::class.java, MediaType.APPLICATION_JSON)).isTrue()
 		assertThat(converter.canRead(Set::class.java, MediaType.APPLICATION_JSON)).isTrue()
+
+		assertThat(converter.canRead(typeTokenOf<List<Int>>(), null, MediaType.APPLICATION_JSON)).isTrue()
+		assertThat(converter.canRead(typeTokenOf<List<SerializableBean>>(), null, MediaType.APPLICATION_JSON)).isTrue()
+		assertThat(converter.canRead(typeTokenOf<ArrayList<Int>>(), null, MediaType.APPLICATION_JSON)).isTrue()
+		assertThat(converter.canRead(typeTokenOf<List<Int>>(), null, MediaType.APPLICATION_PDF)).isFalse()
 	}
 
 	@Test
@@ -60,6 +68,11 @@ class KotlinSerializationJsonHttpMessageConverterTests {
 		assertThat(converter.canWrite(Map::class.java, MediaType.APPLICATION_JSON)).isTrue()
 		assertThat(converter.canWrite(List::class.java, MediaType.APPLICATION_JSON)).isTrue()
 		assertThat(converter.canWrite(Set::class.java, MediaType.APPLICATION_JSON)).isTrue()
+
+		assertThat(converter.canWrite(typeTokenOf<List<Int>>(), null, MediaType.APPLICATION_JSON)).isTrue()
+		assertThat(converter.canWrite(typeTokenOf<List<SerializableBean>>(), null, MediaType.APPLICATION_JSON)).isTrue()
+		assertThat(converter.canWrite(typeTokenOf<ArrayList<Int>>(), null, MediaType.APPLICATION_JSON)).isTrue()
+		assertThat(converter.canWrite(typeTokenOf<List<Int>>(), null, MediaType.APPLICATION_PDF)).isFalse()
 	}
 
 	@Test
@@ -296,4 +309,12 @@ class KotlinSerializationJsonHttpMessageConverterTests {
 	)
 
 	data class NotSerializableBean(val string: String)
+
+	open class TypeBase<T>
+
+	inline fun <reified T> typeTokenOf(): Type {
+		val base = object : TypeBase<T>() {}
+		val superType = base::class.java.genericSuperclass!!
+		return (superType as ParameterizedType).actualTypeArguments.first()!!
+	}
 }

spring-webmvc/src/main/java/org/springframework/web/servlet/config/annotation/WebMvcConfigurationSupport.java

@@ -906,6 +906,9 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 			}
 		}
 
+		if (kotlinSerializationJsonPresent) {
+			messageConverters.add(new KotlinSerializationJsonHttpMessageConverter());
+		}
 		if (jackson2Present) {
 			Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.json();
 			if (this.applicationContext != null) {
@@ -919,9 +922,6 @@ public class WebMvcConfigurationSupport implements ApplicationContextAware, Serv
 		else if (jsonbPresent) {
 			messageConverters.add(new JsonbHttpMessageConverter());
 		}
-		else if (kotlinSerializationJsonPresent) {
-			messageConverters.add(new KotlinSerializationJsonHttpMessageConverter());
-		}
 
 		if (jackson2SmilePresent) {
 			Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.smile();

src/docs/asciidoc/languages/kotlin.adoc

@@ -389,17 +389,13 @@ project for more details.
 === Kotlin multiplatform serialization
 
 As of Spring Framework 5.3, https://github.com/Kotlin/kotlinx.serialization[Kotlin multiplatform serialization] is
-supported in Spring MVC, Spring WebFlux and Spring Messaging. The builtin support currently only targets JSON format.
+supported in Spring MVC, Spring WebFlux and Spring Messaging (RSocket). The builtin support currently only targets JSON format.
-
-To enable it, follow https://github.com/Kotlin/kotlinx.serialization#setup[those instructions] and make sure neither
-Jackson, GSON or JSONB are in the classpath.
-
-NOTE: For a typical Spring Boot web application, that can be achieved by excluding `spring-boot-starter-json` dependency.
-
-In Spring MVC, if you need Jackson, GSON or JSONB for other purposes, you can keep them on the classpath and
-<<web#mvc-config-message-converters, configure message converters>> to remove `MappingJackson2HttpMessageConverter` and add
-`KotlinSerializationJsonHttpMessageConverter`.
 
+To enable it, follow https://github.com/Kotlin/kotlinx.serialization#setup[those instructions] to add the related dependency and plugin.
+With Spring MVC and WebFlux, both Kotlin serialization and Jackson will be configured by default if they are in the classpath since
+Kotlin serialization is designed to serialize only Kotlin classes annotated with `@Serializable`.
+With Spring Messaging (RSocket), make sure that neither Jackson, GSON or JSONB are in the classpath if you want automatic configuration,
+if Jackson is needed configure `KotlinSerializationJsonMessageConverter` manually.
 
 == Coroutines