Add typealias guides into README (#35)

README.md

@@ -124,6 +124,41 @@ public class ExampleService {
     }
     ```
 
+## `typealias` extension
+
+Eventeria provides the `typealias` extension to support following features.
+
+- multiple data formats for single topic.
+- publish the string of message type in fixed string, even if rename of class or relocate package.
+
+When publishing `Message`, the message will contain `typealias` extension that you registered by `addSerializeTypeAlias` or `addCompatibleTypeAlias`. If not, full class name will be used.
+
+When consuming `Message`, eventeria try to deserialize the message with `typealias` extension. You should register typealias by `addDeserializeTypeAlias` or `addCompatibleTypeAlias`.  
+If eventeria failed to find deserialize target type, it try to load class using ClassLoader with provided `typealias` string. If there is no matching class, consuming will be failed.
+
+### Configuration Example
+
+```java
+@Bean
+CloudEventMessageTypeAliasMapper cloudEventMessageTypeAliasMapper() {
+    CloudEventMessageTypeAliasMapper typeAliasMapper = new CloudEventMessageTypeAliasMapper();
+
+    // support typealias at both serialization / deserialization times
+    typeAliasMapper.addCompatibleTypeAlias(
+        PostCreatedEvent.class,
+        "com.navercorp.eventeria.guide.boot.domain.PostCreatedEvent"
+    );
+
+    // support typealias at serialization time only
+    typeAliasMapper.addSerializeTypeAlias(
+        SerializeOnlyTypeAliasPostCreatedEvent.class,
+        "com.navercorp.eventeria.guide.boot.domain.PostCreatedEventSerializeOnlyVersion"
+    );
+
+    return typeAliasMapper;
+}
+```
+
 ## License
 
 ```

guide-projects/spring-boot-eventeria-guide/src/main/java/com/navercorp/eventeria/guide/boot/config/MessageConfig.java

@@ -15,6 +15,7 @@
 
 import com.navercorp.eventeria.guide.boot.domain.AfterPostCreationCommand.NotifyToSubscribers;
 import com.navercorp.eventeria.guide.boot.domain.PostCreatedEvent;
+import com.navercorp.eventeria.guide.boot.domain.SerializeOnlyTypeAliasPostCreatedEvent;
 import com.navercorp.eventeria.messaging.contract.Message;
 import com.navercorp.eventeria.messaging.contract.cloudevents.serializer.CloudEventMessageReaderWriter;
 import com.navercorp.eventeria.messaging.contract.serializer.MessageSerializerDeserializer;
@@ -29,8 +30,6 @@
 @RequiredArgsConstructor
 public class MessageConfig {
 
-	private final ObjectMapper objectMapper;
-
 	static {
 		EventFormatProvider.getInstance()
 			.registerFormat(
@@ -40,6 +39,8 @@ public class MessageConfig {
 			);
 	}
 
+	private final ObjectMapper objectMapper;
+
 	@Bean
 	MessageSerializerDeserializer messageSerializerDeserializer() {
 		return new JacksonMessageSerializer(objectMapper);
@@ -54,6 +55,11 @@ CloudEventMessageTypeAliasMapper cloudEventMessageTypeAliasMapper() {
 			"com.navercorp.eventeria.guide.boot.domain.PostCreatedEvent"
 		);
 
+		typeAliasMapper.addSerializeTypeAlias(
+			SerializeOnlyTypeAliasPostCreatedEvent.class,
+			"com.navercorp.eventeria.guide.boot.domain.PostCreatedEventSerializeOnlyVersion"
+		);
+
 		typeAliasMapper.addCompatibleTypeAlias(
 			NotifyToSubscribers.class,
 			"com.navercorp.eventeria.guide.boot.domain.AfterPostCreationCommand$NotifyToSubscribers"

guide-projects/spring-boot-eventeria-guide/src/main/java/com/navercorp/eventeria/guide/boot/domain/CreatePostService.java

@@ -26,6 +26,10 @@ public Post create(Post post) {
 			PostCreatedEvent.from(post)
 		);
 
+		springMessagePublisher.publish(
+			SerializeOnlyTypeAliasPostCreatedEvent.from(post)
+		);
+
 		return post;
 	}
 }

guide-projects/spring-boot-eventeria-guide/src/main/java/com/navercorp/eventeria/guide/boot/domain/PostEventHandler.java

@@ -35,4 +35,18 @@ public void publishAfterPostCreatedCommands(
 			)
 		);
 	}
+
+	public void publishAfterPostCreatedCommands(
+		SerializeOnlyTypeAliasPostCreatedEvent event
+	) {
+		log.info("[CONSUME][Programmatic][SerializeOnlyTypeAliasPostCreatedEvent] {}", event);
+
+		springMessagePublisher.publish(
+			List.of(
+				UpdateUserStatistic.of(event.getPostId(), event.getWriterId()),
+				RefreshPostRanking.from(event.getPostId()),
+				ApplySearchIndex.from(event.getPostId())
+			)
+		);
+	}
 }

guide-projects/spring-boot-eventeria-guide/src/main/java/com/navercorp/eventeria/guide/boot/domain/SerializeOnlyTypeAliasPostCreatedEvent.java

@@ -0,0 +1,32 @@
+package com.navercorp.eventeria.guide.boot.domain;
+
+import lombok.AccessLevel;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.ToString;
+
+import com.navercorp.eventeria.messaging.contract.event.AbstractDomainEvent;
+
+@Getter
+@ToString(callSuper = true)
+@NoArgsConstructor(access = AccessLevel.PRIVATE)
+public class SerializeOnlyTypeAliasPostCreatedEvent extends AbstractDomainEvent {
+
+	private long postId;
+	private String writerId;
+
+	public SerializeOnlyTypeAliasPostCreatedEvent(long postId, String writerId) {
+		super(String.valueOf(postId));
+		this.postId = postId;
+		this.writerId = writerId;
+	}
+
+	public static SerializeOnlyTypeAliasPostCreatedEvent from(Post post) {
+		return new SerializeOnlyTypeAliasPostCreatedEvent(post.id(), post.writerId());
+	}
+
+	@Override
+	public String getSourceType() {
+		return Post.class.getName();
+	}
+}

guide-projects/spring-boot-eventeria-guide/src/main/java/com/navercorp/eventeria/guide/boot/listener/ProgrammaticBindingEventListener.java

@@ -14,6 +14,7 @@
 
 import com.navercorp.eventeria.guide.boot.domain.PostCreatedEvent;
 import com.navercorp.eventeria.guide.boot.domain.PostEventHandler;
+import com.navercorp.eventeria.guide.boot.domain.SerializeOnlyTypeAliasPostCreatedEvent;
 import com.navercorp.eventeria.messaging.contract.cloudevents.converter.CloudEventToMessageConverter;
 import com.navercorp.eventeria.messaging.spring.cloud.stream.binding.InboundChannelBinder;
 import com.navercorp.eventeria.messaging.spring.integration.channel.SpringMessageHandler;
@@ -98,6 +99,7 @@ MessagePayloadTypeRouter postEventRouter(
 	) {
 		return MessagePayloadTypeRouter.register(INBOUND_BEAN_NAME)
 			.route(PostCreatedEvent.class, postEventHandler::publishAfterPostCreatedCommands)
+			.route(SerializeOnlyTypeAliasPostCreatedEvent.class, postEventHandler::publishAfterPostCreatedCommands)
 			.done();
 	}
 }

guide-projects/spring-boot-eventeria-guide/src/test/java/com/navercorp/eventeria/guide/boot/controller/PostApiControllerIntegrationTest.java

@@ -64,7 +64,7 @@ void registerPost() {
 	}
 
 	private void assertPublishedMessageCount() {
-		int expectedPostEventCount = 1;
+		int expectedPostEventCount = 1 + 1; // PostCreatedEvent + SerializeOnlyTypeAliasPostCreatedEvent
 		int expectedAfterPostCommandCount = 3;
 		int expectedNotifyCommandCount = 1;
 
@@ -88,7 +88,11 @@ private void assertPublishedMessageCount() {
 			throw new RuntimeException(e);
 		}
 
+		// PostCreatedEvent + SerializeOnlyTypeAliasPostCreatedEvent published
 		then(actualPostEventCounter.get()).isEqualTo(expectedPostEventCount);
+
+		// continuous command published for PostCreatedEvent only.
+		// Because failed to deserialize SerializeOnlyTypeAliasPostCreatedEvent
 		then(actualAfterPostCommandCounter.get()).isEqualTo(expectedAfterPostCommandCount);
 		then(actualNotifyCommandCounter.get()).isEqualTo(expectedNotifyCommandCount);
 	}