Refactor CloudEvents package structure

Remove v1 subpackage and flatten the CloudEvents package hierarchy.
Introduce strategy pattern for format conversion to replace enum-based approach,
improving extensibility and reduce dependencies.

Key changes:
- Move all classes from cloudevents.v1 to cloudevents base package
- Remove optional format dependencies (JSON, XML, Avro) from build
- Replace `ConversionType` enum with `FormatStrategy` interface
- Add `CloudEventMessageFormatStrategy` as default implementation
- Inline `HeaderPatternMatcher` logic into `ToCloudEventTransformerExtensions`
- Add `@NullMarked` package annotations and `@Nullable` throughout
- Document `targetClass` parameter behavior in `CloudEventMessageConverter`
- Split transformer tests for better organization and coverage
- Update component type identifier to "ce:to-cloudevents-transformer"
- Remove unnecessary docs from package-info

Author: cppwfs

build.gradle

@@ -474,20 +474,10 @@ project('spring-integration-cassandra') {
 }
 
 project('spring-integration-cloudevents') {
-    description = 'Spring Integration Cloud Events Support'
+    description = 'Spring Integration CloudEvents Support'
 
     dependencies {
         api "io.cloudevents:cloudevents-core:$cloudEventsVersion"
-        optionalApi "io.cloudevents:cloudevents-json-jackson:$cloudEventsVersion"
-
-        optionalApi("io.cloudevents:cloudevents-avro-compact:$cloudEventsVersion") {
-            exclude group: 'org.apache.avro', module: 'avro'
-        }
-        optionalApi "org.apache.avro:avro:$avroVersion"
-        optionalApi "io.cloudevents:cloudevents-xml:$cloudEventsVersion"
-        optionalApi 'org.jspecify:jspecify'
-
-        testImplementation 'org.springframework.amqp:spring-rabbit-test'
     }
 }
 

spring-integration-cloudevents/src/main/java/org/springframework/integration/cloudevents/v1/CloudEventMessageConverter.java renamed to spring-integration-cloudevents/src/main/java/org/springframework/integration/cloudevents/CloudEventMessageConverter.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.springframework.integration.cloudevents.v1;
+package org.springframework.integration.cloudevents;
 
 import java.nio.charset.StandardCharsets;
 
@@ -25,6 +25,7 @@
 import io.cloudevents.core.message.MessageReader;
 import io.cloudevents.core.message.impl.GenericStructuredMessageReader;
 import io.cloudevents.core.message.impl.MessageUtils;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageHeaders;
@@ -42,7 +43,7 @@
  */
 public class CloudEventMessageConverter implements MessageConverter {
 
-	private String cePrefix;
+	private final String cePrefix;
 
 	public CloudEventMessageConverter(String cePrefix) {
 		this.cePrefix = cePrefix;
@@ -52,28 +53,35 @@ public CloudEventMessageConverter() {
 		this(CloudEventsHeaders.CE_PREFIX);
 	}
 
+	/**
+	 Convert the payload of a Message from a CloudEvent to a typed Object of the specified target class.
+	 If the converter does not support the specified media type or cannot perform the conversion, it should return null.
+	 * @param message the input message
+	 * @param targetClass This method does not check the class since it is expected to be a {@link CloudEvent}
+	 * @return the result of the conversion, or null if the converter cannot perform the conversion
+	 */
 	@Override
 	public Object fromMessage(Message<?> message, Class<?> targetClass) {
-		Assert.state(CloudEvent.class.isAssignableFrom(targetClass), "Target class must be a CloudEvent");
 		return createMessageReader(message).toEvent();
 	}
 
 	@Override
-	public Message<?> toMessage(Object payload, MessageHeaders headers) {
+	public Message<?> toMessage(Object payload, @Nullable MessageHeaders headers) {
 		Assert.state(payload instanceof CloudEvent, "Payload must be a CloudEvent");
+		Assert.state(headers != null, "Headers must not be null");
 		return CloudEventUtils.toReader((CloudEvent) payload).read(new MessageBuilderMessageWriter(headers, this.cePrefix));
 	}
 
 	private MessageReader createMessageReader(Message<?> message) {
-		return MessageUtils.parseStructuredOrBinaryMessage(//
-				() -> contentType(message.getHeaders()), //
-				format -> structuredMessageReader(message, format), //
-				() -> version(message.getHeaders()), //
-				version -> binaryMessageReader(message, version) //
+		return MessageUtils.parseStructuredOrBinaryMessage(
+				() -> contentType(message.getHeaders()),
+				format -> structuredMessageReader(message, format),
+				() -> version(message.getHeaders()),
+				version -> binaryMessageReader(message, version)
 		);
 	}
 
-	private String version(MessageHeaders message) {
+	private @Nullable String version(MessageHeaders message) {
 		if (message.containsKey(CloudEventsHeaders.SPEC_VERSION)) {
 			return message.get(CloudEventsHeaders.SPEC_VERSION).toString();
 		}
@@ -88,7 +96,7 @@ private MessageReader structuredMessageReader(Message<?> message, EventFormat fo
 		return new GenericStructuredMessageReader(format, getBinaryData(message));
 	}
 
-	private String contentType(MessageHeaders message) {
+	private @Nullable String contentType(MessageHeaders message) {
 		if (message.containsKey(MessageHeaders.CONTENT_TYPE)) {
 			return message.get(MessageHeaders.CONTENT_TYPE).toString();
 		}

spring-integration-cloudevents/src/main/java/org/springframework/integration/cloudevents/v1/CloudEventsHeaders.java renamed to spring-integration-cloudevents/src/main/java/org/springframework/integration/cloudevents/CloudEventsHeaders.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.springframework.integration.cloudevents.v1;
+package org.springframework.integration.cloudevents;
 
 /**
  * Constants for Cloud Events header names.

spring-integration-cloudevents/src/main/java/org/springframework/integration/cloudevents/v1/MessageBinaryMessageReader.java renamed to spring-integration-cloudevents/src/main/java/org/springframework/integration/cloudevents/MessageBinaryMessageReader.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.springframework.integration.cloudevents.v1;
+package org.springframework.integration.cloudevents;
 
 import java.util.Map;
 import java.util.function.BiConsumer;
@@ -23,6 +23,7 @@
 import io.cloudevents.core.data.BytesCloudEventData;
 import io.cloudevents.core.impl.StringUtils;
 import io.cloudevents.core.message.impl.BaseGenericBinaryMessageReaderImpl;
+import org.jspecify.annotations.Nullable;
 
 /**
  * Utility for converting maps (message headers) to `CloudEvent` contexts.
@@ -34,11 +35,12 @@
  *
  */
 public class MessageBinaryMessageReader extends BaseGenericBinaryMessageReaderImpl<String, Object> {
+
 	private final String cePrefix;
 
 	private final Map<String, Object> headers;
 
-	public MessageBinaryMessageReader(SpecVersion version, Map<String, Object> headers, byte[] payload, String cePrefix) {
+	public MessageBinaryMessageReader(SpecVersion version, Map<String, Object> headers, byte @Nullable [] payload, String cePrefix) {
 		super(version, payload == null ? null : BytesCloudEventData.wrap(payload));
 		this.headers = headers;
 		this.cePrefix = cePrefix;
@@ -55,7 +57,7 @@ protected boolean isContentTypeHeader(String key) {
 
 	@Override
 	protected boolean isCloudEventsHeader(String key) {
-		return key != null && key.length() > this.cePrefix.length() && StringUtils.startsWithIgnoreCase(key, this.cePrefix);
+		return key.length() > this.cePrefix.length() && StringUtils.startsWithIgnoreCase(key, this.cePrefix);
 	}
 
 	@Override

spring-integration-cloudevents/src/main/java/org/springframework/integration/cloudevents/v1/MessageBuilderMessageWriter.java renamed to spring-integration-cloudevents/src/main/java/org/springframework/integration/cloudevents/MessageBuilderMessageWriter.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.springframework.integration.cloudevents.v1;
+package org.springframework.integration.cloudevents;
 
 import java.util.HashMap;
 import java.util.Map;
@@ -26,6 +26,7 @@
 import io.cloudevents.rw.CloudEventContextWriter;
 import io.cloudevents.rw.CloudEventRWException;
 import io.cloudevents.rw.CloudEventWriter;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.messaging.Message;
 import org.springframework.messaging.support.MessageBuilder;
@@ -62,7 +63,7 @@ public Message<byte[]> setEvent(EventFormat format, byte[] value) throws CloudEv
 	}
 
 	@Override
-	public Message<byte[]> end(CloudEventData value) throws CloudEventRWException {
+	public Message<byte[]> end(@Nullable CloudEventData value) throws CloudEventRWException {
 		return MessageBuilder.withPayload(value == null ? new byte[0] : value.toBytes()).copyHeaders(this.headers).build();
 	}
 

spring-integration-cloudevents/src/main/java/org/springframework/integration/cloudevents/package-info.java

@@ -0,0 +1,3 @@
+
+@org.jspecify.annotations.NullMarked
+package org.springframework.integration.cloudevents;

spring-integration-cloudevents/src/main/java/org/springframework/integration/cloudevents/v1/transformer/CloudEventProperties.java renamed to spring-integration-cloudevents/src/main/java/org/springframework/integration/cloudevents/transformer/CloudEventProperties.java

@@ -14,14 +14,14 @@
  * limitations under the License.
  */
 
-package org.springframework.integration.cloudevents.v1.transformer;
+package org.springframework.integration.cloudevents.transformer;
 
 import java.net.URI;
 import java.time.OffsetDateTime;
 
 import org.jspecify.annotations.Nullable;
 
-import org.springframework.integration.cloudevents.v1.CloudEventsHeaders;
+import org.springframework.integration.cloudevents.CloudEventsHeaders;
 
 /**
  * Configuration properties for CloudEvent metadata and formatting.

spring-integration-cloudevents/src/main/java/org/springframework/integration/cloudevents/v1/transformer/ToCloudEventTransformer.java renamed to spring-integration-cloudevents/src/main/java/org/springframework/integration/cloudevents/transformer/ToCloudEventTransformer.java

@@ -14,28 +14,20 @@
  * limitations under the License.
  */
 
-package org.springframework.integration.cloudevents.v1.transformer;
-
-import java.util.HashMap;
-import java.util.Map;
-import java.util.Objects;
+package org.springframework.integration.cloudevents.transformer;
 
 import io.cloudevents.CloudEvent;
-import io.cloudevents.avro.compact.AvroCompactFormat;
 import io.cloudevents.core.builder.CloudEventBuilder;
-import io.cloudevents.jackson.JsonFormat;
-import io.cloudevents.xml.XMLFormat;
 import org.jspecify.annotations.Nullable;
 
-import org.springframework.integration.cloudevents.v1.CloudEventMessageConverter;
-import org.springframework.integration.cloudevents.v1.transformer.utils.HeaderPatternMatcher;
+import org.springframework.integration.cloudevents.CloudEventMessageConverter;
+import org.springframework.integration.cloudevents.CloudEventsHeaders;
+import org.springframework.integration.cloudevents.transformer.strategies.CloudEventMessageFormatStrategy;
+import org.springframework.integration.cloudevents.transformer.strategies.FormatStrategy;
 import org.springframework.integration.transformer.AbstractTransformer;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageHeaders;
-import org.springframework.messaging.converter.MessageConversionException;
 import org.springframework.messaging.converter.MessageConverter;
-import org.springframework.messaging.support.MessageBuilder;
-import org.springframework.util.Assert;
 
 /**
  * A Spring Integration transformer that converts messages to CloudEvent format.
@@ -62,24 +54,11 @@
  */
 public class ToCloudEventTransformer extends AbstractTransformer {
 
-	/**
-	 * Enumeration of supported CloudEvent conversion types.
-	 * <p>
-	 * Defines the different output formats supported by the transformer:
-	 * <ul>
-	 *   <li>DEFAULT - No format conversion, uses standard CloudEvent message structure</li>
-	 *   <li>XML - Serializes CloudEvent as XML in the message payload</li>
-	 *   <li>JSON - Serializes CloudEvent as JSON in the message payload</li>
-	 *   <li>AVRO - Serializes CloudEvent as compact Avro binary in the message payload</li>
-	 * </ul>
-	 */
-	public enum ConversionType { DEFAULT, XML, JSON, AVRO }
-
 	private final MessageConverter messageConverter;
 
 	private final @Nullable String cloudEventExtensionPatterns;
 
-	private final ConversionType conversionType;
+	private final FormatStrategy formatStrategy;
 
 	private final CloudEventProperties cloudEventProperties;
 
@@ -90,19 +69,20 @@ public enum ConversionType { DEFAULT, XML, JSON, AVRO }
 	 * supports wildcards and negation with '!' prefix   If a header matches one of the '!' it is excluded from
 	 * cloud event headers and the message headers.   If a header does not match for a prefix or a exclusion, the header
 	 * is left in the message headers.   . Null to disable extension mapping.
-	 * @param conversionType the output format for the CloudEvent (DEFAULT, XML, JSON, or AVRO)
+	 * @param formatStrategy The strategy that determines how the CloudEvent will be rendered
 	 * @param cloudEventProperties configuration properties for CloudEvent metadata (id, source, type, etc.)
 	 */
 	public ToCloudEventTransformer(@Nullable String cloudEventExtensionPatterns,
-			ConversionType conversionType, CloudEventProperties cloudEventProperties) {
+			FormatStrategy formatStrategy, CloudEventProperties cloudEventProperties) {
 		this.messageConverter = new CloudEventMessageConverter(cloudEventProperties.getCePrefix());
 		this.cloudEventExtensionPatterns = cloudEventExtensionPatterns;
-		this.conversionType = conversionType;
+		this.formatStrategy = formatStrategy;
 		this.cloudEventProperties = cloudEventProperties;
 	}
 
 	public ToCloudEventTransformer() {
-		this(null, ConversionType.DEFAULT, new CloudEventProperties());
+		this(null, new CloudEventMessageFormatStrategy(CloudEventsHeaders.CE_PREFIX),
+				new CloudEventProperties());
 	}
 
 	/**
@@ -135,75 +115,7 @@ protected Object doTransform(Message<?> message) {
 				.withData(getPayloadAsBytes(message.getPayload()))
 				.withExtension(extensions)
 				.build();
-
-		switch (this.conversionType) {
-			case XML:
-				return convertToXmlMessage(cloudEvent, message.getHeaders());
-			case JSON:
-				return convertToJsonMessage(cloudEvent, message.getHeaders());
-			case AVRO:
-				return convertToAvroMessage(cloudEvent, message.getHeaders());
-			default:
-				var result = this.messageConverter.toMessage(cloudEvent, filterHeaders(message.getHeaders()));
-				Assert.state(result != null, "Payload result must not be null");
-				return result;
-		}
-	}
-
-	private Message<String> convertToXmlMessage(CloudEvent cloudEvent, MessageHeaders originalHeaders) {
-		XMLFormat xmlFormat = new XMLFormat();
-		String xmlContent = new String(xmlFormat.serialize(cloudEvent));
-		return buildStringMessage(xmlContent, originalHeaders, "application/xml");
-	}
-
-	private Message<String> convertToJsonMessage(CloudEvent cloudEvent, MessageHeaders originalHeaders) {
-		JsonFormat jsonFormat = new JsonFormat();
-		String jsonContent = new String(jsonFormat.serialize(cloudEvent));
-		return buildStringMessage(jsonContent, originalHeaders, "application/json");
-	}
-
-	private Message<String> buildStringMessage(String serializedCloudEvent,
-			MessageHeaders originalHeaders, String contentType) {
-		try {
-			return MessageBuilder.withPayload(serializedCloudEvent)
-					.copyHeaders(filterHeaders(originalHeaders))
-					.setHeader("content-type", contentType)
-					.build();
-		}
-		catch (Exception e) {
-			throw new MessageConversionException("Failed to convert CloudEvent to " + contentType, e);
-		}
-	}
-
-	private Message<byte[]> convertToAvroMessage(CloudEvent cloudEvent, MessageHeaders originalHeaders) {
-		try {
-			AvroCompactFormat avroFormat = new AvroCompactFormat();
-			byte[] avroBytes = avroFormat.serialize(cloudEvent);
-			return MessageBuilder.withPayload(avroBytes)
-					.copyHeaders(filterHeaders(originalHeaders))
-					.setHeader("content-type", "application/avro")
-					.build();
-		}
-		catch (Exception e) {
-			throw new RuntimeException("Failed to convert CloudEvent to application/avro", e);
-		}
-	}
-
-	/**
-	 * This method creates a {@link MessageHeaders} that were not placed in the CloudEvent and were not excluded via the
-	 * categorization mechanism.
-	 * @param headers The {@link MessageHeaders} to be filtered.
-	 * @return {@link MessageHeaders} that have been filtered.
-	 */
-	private MessageHeaders filterHeaders(MessageHeaders headers) {
-
-		Map<String, Object> filteredHeaders = new HashMap<>();
-		headers.keySet().forEach(key -> {
-			if (HeaderPatternMatcher.categorizeHeader(key, this.cloudEventExtensionPatterns) == null) {
-				filteredHeaders.put(key, Objects.requireNonNull(headers.get(key)));
-			}
-		});
-		return new MessageHeaders(filteredHeaders);
+				return this.formatStrategy.convert(cloudEvent, new MessageHeaders(extensions.getFilteredHeaders()));
 	}
 
 	private byte[] getPayloadAsBytes(Object payload) {
@@ -220,7 +132,7 @@ else if (payload instanceof String stringPayload) {
 
 	@Override
 	public String getComponentType() {
-		return "to-cloud-transformer";
+		return "ce:to-cloudevents-transformer";
 	}
 
 }