GH-756 - Avoid superfluous, repeated deserialization in JdbcEventPublication.getEvent().

Author: odrotbohm

spring-modulith-events/spring-modulith-events-jdbc/src/main/java/org/springframework/modulith/events/jdbc/JdbcEventPublicationRepository.java

@@ -25,6 +25,7 @@
 import java.util.Objects;
 import java.util.Optional;
 import java.util.UUID;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
 
@@ -323,7 +324,8 @@ private TargetEventPublication resultSetToPublication(ResultSet rs) throws SQLEx
 		var listenerId = rs.getString("LISTENER_ID");
 		var serializedEvent = rs.getString("SERIALIZED_EVENT");
 
-		return new JdbcEventPublication(id, publicationDate, listenerId, serializedEvent, eventClass, serializer,
+		return new JdbcEventPublication(id, publicationDate, listenerId,
+				() -> serializer.deserialize(serializedEvent, eventClass),
 				completionDate == null ? null : completionDate.toInstant());
 	}
 
@@ -368,11 +370,10 @@ private static class JdbcEventPublication implements TargetEventPublication {
 		private final UUID id;
 		private final Instant publicationDate;
 		private final String listenerId;
-		private final String serializedEvent;
-		private final Class<?> eventType;
+		private final Supplier<Object> eventSupplier;
 
-		private final EventSerializer serializer;
 		private @Nullable Instant completionDate;
+		private @Nullable Object event;
 
 		/**
 		 * @param id must not be {@literal null}.
@@ -383,22 +384,17 @@ private static class JdbcEventPublication implements TargetEventPublication {
 		 * @param serializer must not be {@literal null}.
 		 * @param completionDate can be {@literal null}.
 		 */
-		public JdbcEventPublication(UUID id, Instant publicationDate, String listenerId, String serializedEvent,
-				Class<?> eventType, EventSerializer serializer, @Nullable Instant completionDate) {
+		public JdbcEventPublication(UUID id, Instant publicationDate, String listenerId, Supplier<Object> event,
+				@Nullable Instant completionDate) {
 
 			Assert.notNull(id, "Id must not be null!");
 			Assert.notNull(publicationDate, "Publication date must not be null!");
 			Assert.hasText(listenerId, "Listener id must not be null or empty!");
-			Assert.hasText(serializedEvent, "Serialized event must not be null or empty!");
-			Assert.notNull(eventType, "Event type must not be null!");
-			Assert.notNull(serializer, "EventSerializer must not be null!");
 
 			this.id = id;
 			this.publicationDate = publicationDate;
 			this.listenerId = listenerId;
-			this.serializedEvent = serializedEvent;
-			this.eventType = eventType;
-			this.serializer = serializer;
+			this.eventSupplier = event;
 			this.completionDate = completionDate;
 		}
 
@@ -416,8 +412,14 @@ public UUID getIdentifier() {
 		 * @see org.springframework.modulith.events.EventPublication#getEvent()
 		 */
 		@Override
+		@SuppressWarnings("null")
 		public Object getEvent() {
-			return serializer.deserialize(serializedEvent, eventType);
+
+			if (event == null) {
+				this.event = eventSupplier.get();
+			}
+
+			return event;
 		}
 
 		/*
@@ -481,12 +483,10 @@ public boolean equals(@Nullable Object obj) {
 			}
 
 			return Objects.equals(completionDate, that.completionDate) //
-					&& Objects.equals(eventType, that.eventType) //
 					&& Objects.equals(id, that.id) //
 					&& Objects.equals(listenerId, that.listenerId) //
 					&& Objects.equals(publicationDate, that.publicationDate) //
-					&& Objects.equals(serializedEvent, that.serializedEvent) //
-					&& Objects.equals(serializer, that.serializer);
+					&& Objects.equals(getEvent(), that.getEvent());
 		}
 
 		/*
@@ -495,7 +495,7 @@ public boolean equals(@Nullable Object obj) {
 		 */
 		@Override
 		public int hashCode() {
-			return Objects.hash(completionDate, eventType, id, listenerId, publicationDate, serializedEvent, serializer);
+			return Objects.hash(completionDate, id, listenerId, publicationDate, getEvent());
 		}
 	}
 }

spring-modulith-events/spring-modulith-events-jdbc/src/test/java/org/springframework/modulith/events/jdbc/JdbcEventPublicationRepositoryIntegrationTests.java

@@ -310,6 +310,25 @@ void findsCompletedPublications() {
 					.isEqualTo(event);
 		}
 
+		@Test // GH-753
+		void returnsSameEventInstanceFromPublication() {
+
+			// An event not implementing equals(…) / hashCode()
+			var event = new Sample();
+
+			// Serialize to whatever
+			doReturn("").when(serializer).serialize(event);
+
+			// Return fresh instances for every deserialization attempt
+			doAnswer(__ -> new Sample()).when(serializer).deserialize("", Sample.class);
+
+			repository.create(TargetEventPublication.of(event, TARGET_IDENTIFIER));
+
+			var publication = repository.findIncompletePublications().get(0);
+
+			assertThat(publication.getEvent()).isSameAs(publication.getEvent());
+		}
+
 		private TargetEventPublication createPublication(Object event) {
 
 			var token = event.toString();
@@ -343,4 +362,6 @@ class MySQL extends TestBase {}
 	private static final class TestEvent {
 		String eventId;
 	}
+
+	private static final class Sample {}
 }