Better generci types in JsonSerde/JsonDeserializer

* bounded wildcards for JsonDeserializer targetType

* added deserializer type inference test, modified @author list

* fixed checkstyle error

Author: inponomarev

spring-kafka/src/main/java/org/springframework/kafka/support/serializer/JsonDeserializer.java

@@ -53,6 +53,7 @@
  * @author Yanming Zhou
  * @author Elliot Kennedy
  * @author Torsten Schleede
+ * @author Ivan Ponomarev
  */
 public class JsonDeserializer<T> implements ExtendedDeserializer<T> {
 
@@ -138,7 +139,7 @@ public JsonDeserializer(ObjectMapper objectMapper) {
 	 * {@link ObjectMapper}.
 	 * @param targetType the target type to use if no type info headers are present.
 	 */
-	public JsonDeserializer(Class<T> targetType) {
+	public JsonDeserializer(Class<? super T> targetType) {
 		this(targetType, true);
 	}
 
@@ -150,7 +151,7 @@ public JsonDeserializer(Class<T> targetType) {
 	 * type if not.
 	 * @since 2.2
 	 */
-	public JsonDeserializer(Class<T> targetType, boolean useHeadersIfPresent) {
+	public JsonDeserializer(Class<? super T> targetType, boolean useHeadersIfPresent) {
 		this(targetType, new ObjectMapper(), useHeadersIfPresent, om -> {
 			om.configure(MapperFeature.DEFAULT_VIEW_INCLUSION, false);
 			om.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
@@ -162,7 +163,7 @@ public JsonDeserializer(Class<T> targetType, boolean useHeadersIfPresent) {
 	 * @param targetType the target type to use if no type info headers are present.
 	 * @param objectMapper the mapper. type if not.
 	 */
-	public JsonDeserializer(Class<T> targetType, ObjectMapper objectMapper) {
+	public JsonDeserializer(Class<? super T> targetType, ObjectMapper objectMapper) {
 		this(targetType, objectMapper, true);
 	}
 
@@ -175,17 +176,17 @@ public JsonDeserializer(Class<T> targetType, ObjectMapper objectMapper) {
 	 * type if not.
 	 * @since 2.2
 	 */
-	public JsonDeserializer(@Nullable Class<T> targetType, ObjectMapper objectMapper, boolean useHeadersIfPresent) {
+	public JsonDeserializer(@Nullable Class<? super T> targetType, ObjectMapper objectMapper, boolean useHeadersIfPresent) {
 		this(targetType, objectMapper, useHeadersIfPresent, om -> { });
 	}
 
 	@SuppressWarnings("unchecked")
-	private JsonDeserializer(@Nullable Class<T> targetType, ObjectMapper objectMapper, boolean useHeadersIfPresent,
+	private JsonDeserializer(@Nullable Class<? super T> targetType, ObjectMapper objectMapper, boolean useHeadersIfPresent,
 			Consumer<ObjectMapper> configurer) {
 
 		Assert.notNull(objectMapper, "'objectMapper' must not be null.");
 		this.objectMapper = objectMapper;
-		this.targetType = targetType;
+		this.targetType = (Class<T>) targetType;
 		if (this.targetType == null) {
 			this.targetType = (Class<T>) ResolvableType.forClass(getClass()).getSuperType().resolveGeneric(0);
 		}

spring-kafka/src/main/java/org/springframework/kafka/support/serializer/JsonSerde.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2017-2018 the original author or authors.
+ * Copyright 2017-2019 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.
@@ -42,6 +42,7 @@
  * @author Marius Bogoevici
  * @author Elliot Kennedy
  * @author Gary Russell
+ * @author Ivan Ponomarev
  *
  * @since 1.1.5
  */
@@ -55,7 +56,7 @@ public JsonSerde() {
 		this((ObjectMapper) null);
 	}
 
-	public JsonSerde(Class<T> targetType) {
+	public JsonSerde(Class<? super T> targetType) {
 		this(targetType, null);
 	}
 
@@ -64,9 +65,9 @@ public JsonSerde(ObjectMapper objectMapper) {
 	}
 
 	@SuppressWarnings("unchecked")
-	public JsonSerde(@Nullable Class<T> targetTypeArg, @Nullable ObjectMapper objectMapperArg) {
+	public JsonSerde(@Nullable Class<? super T> targetTypeArg, @Nullable ObjectMapper objectMapperArg) {
 		ObjectMapper objectMapper = objectMapperArg;
-		Class<T> targetType = targetTypeArg;
+		Class<T> targetType = (Class<T>) targetTypeArg;
 		if (objectMapper == null) {
 			objectMapper = new ObjectMapper();
 			objectMapper.configure(MapperFeature.DEFAULT_VIEW_INCLUSION, false);

spring-kafka/src/test/java/org/springframework/kafka/support/serializer/JsonSerializationTests.java

@@ -46,6 +46,7 @@
  * @author Yanming Zhou
  * @author Torsten Schleede
  * @author Gary Russell
+ * @author Ivan Ponomarev
  */
 public class JsonSerializationTests {
 
@@ -83,18 +84,18 @@ public void init() {
 		topic = "topic-name";
 
 		jsonReader = new JsonDeserializer<DummyEntity>() { };
-		jsonReader.configure(new HashMap<String, Object>(), false);
+		jsonReader.configure(new HashMap<>(), false);
 		jsonReader.close(); // does nothing, so may be called any time, or not called at all
 		jsonArrayReader = new JsonDeserializer<DummyEntity[]>() { };
-		jsonArrayReader.configure(new HashMap<String, Object>(), false);
+		jsonArrayReader.configure(new HashMap<>(), false);
 		jsonArrayReader.close(); // does nothing, so may be called any time, or not called at all
 		jsonWriter = new JsonSerializer<>();
-		jsonWriter.configure(new HashMap<String, Object>(), false);
+		jsonWriter.configure(new HashMap<>(), false);
 		jsonWriter.close(); // does nothing, so may be called any time, or not called at all
 		stringReader = new StringDeserializer();
-		stringReader.configure(new HashMap<String, Object>(), false);
+		stringReader.configure(new HashMap<>(), false);
 		stringWriter = new StringSerializer();
-		stringWriter.configure(new HashMap<String, Object>(), false);
+		stringWriter.configure(new HashMap<>(), false);
 		dummyEntityJsonDeserializer = new DummyEntityJsonDeserializer();
 		dummyEntityArrayJsonDeserializer = new DummyEntityArrayJsonDeserializer();
 	}
@@ -203,6 +204,14 @@ public void testDeserTypeHeadersConfig() {
 			.isEqualTo(TypePrecedence.INFERRED);
 	}
 
+	@Test
+	public void testDeserializerTypeInference() {
+		JsonSerializer<List<String>> ser = new JsonSerializer<>();
+		JsonDeserializer<List<String>> de = new JsonDeserializer<>(List.class);
+		List<String> dummy = Arrays.asList("foo", "bar", "baz");
+		assertThat(de.deserialize(topic, ser.serialize(topic, dummy))).isEqualTo(dummy);
+	}
+
 	static class DummyEntityJsonDeserializer extends JsonDeserializer<DummyEntity> {
 
 	}