fix(track): dates are serialized as integer array instead of iso string

services/track/src/main/java/de/codecentric/habitcentric/track/CustomJsonSerializer.java

@@ -0,0 +1,33 @@
+package de.codecentric.habitcentric.track;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import org.springframework.kafka.support.JacksonUtils;
+import org.springframework.kafka.support.serializer.JsonSerializer;
+
+/**
+ * Custom Spring Kafka {@link JsonSerializer} that serializes timestamps as strings instead of
+ * integer arrays.
+ *
+ * <p>For some reason, Spring Boot does not use the auto-configured {@link ObjectMapper} when
+ * auto-configuring Spring Kafka. Instead, it calls the no-args constructor of the {@link
+ * JsonSerializer} class provided by the property {@code spring.kafka.producer.value-serializer}.
+ *
+ * @param <T>
+ * @see <a
+ *     href="https://github.com/spring-projects/spring-kafka/issues/680">https://github.com/spring-projects/spring-kafka/issues/680</a>
+ * @see <a
+ *     href="https://docs.spring.io/spring-kafka/reference/tips.html#tip-json">https://docs.spring.io/spring-kafka/reference/tips.html#tip-json</a>
+ */
+public class CustomJsonSerializer<T> extends JsonSerializer<T> {
+
+  public CustomJsonSerializer() {
+    super(createMapper());
+  }
+
+  private static ObjectMapper createMapper() {
+    var mapper = JacksonUtils.enhancedObjectMapper();
+    mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
+    return mapper;
+  }
+}

services/track/src/main/resources/application.yml

@@ -11,6 +11,7 @@ spring:
   flyway.schemas: hc_track
   jackson:
     serialization:
+      WRITE_DATES_AS_TIMESTAMPS: false
       FAIL_ON_EMPTY_BEANS: false
   jpa:
     database-platform: postgres
@@ -36,6 +37,7 @@ spring:
     producer:
       properties:
         "spring.json.type.mapping": "date-tracked:de.codecentric.habitcentric.track.habit.HabitTracking$DateTracked,date-untracked:de.codecentric.habitcentric.track.habit.HabitTracking$DateUntracked"
+      value-serializer: de.codecentric.habitcentric.track.CustomJsonSerializer
 
 server:
   port: 9002

services/track/src/test/java/de/codecentric/habitcentric/track/CustomJsonSerializerTest.java

@@ -0,0 +1,15 @@
+package de.codecentric.habitcentric.track;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class CustomJsonSerializerTest {
+
+  @Test
+  void creates() {
+    try (var subject = new CustomJsonSerializer<>()) {
+      assertThat(subject).isNotNull();
+    }
+  }
+}