Improve RabbitAmqpUtils.toAmqpMessage()

The `RabbitAmqpUtils.toAmqpMessage()` utility is used on the publisher side,
so, it is natural to treat such a message as a reply.
Therefore, the `correlationId` is set to `messageId` of `correlationId` is not present.
The `replyTo` of the Spring message is set into `to` of the AMQP message

* Mention in the `Address` JavaDocs that just `routingKey` can be treated differently by clients
* Fix error message in the `RabbitAmqpMessageListenerAdapter`

Author: artembilan

spring-amqp/src/main/java/org/springframework/amqp/core/Address.java

@@ -23,8 +23,8 @@
 import org.springframework.util.StringUtils;
 
 /**
- * Represents an address for publication of an AMQP message. The AMQP 0-8 and 0-9
- * specifications have an unstructured string that is used as a "reply to" address.
+ * Represents an address for publication of an AMQP message. The AMQP 0.9
+ * specification has an unstructured string that is used as a "reply to" address.
  * There are however conventions in use and this class makes it easier to
  * follow these conventions, which can be easily summarised as:
  *
@@ -33,7 +33,10 @@
  * </pre>
  *
  * Here we also the exchange name to default to empty
- * (so just a routing key will work if you know the queue name).
+ * (so just a routing key will work as a queue name).
+ * <p>
+ * For AMQP 1.0, only routing key is treated as target destination.
+ *
  *
  * @author Mark Pollack
  * @author Mark Fisher
@@ -58,11 +61,11 @@ public class Address {
 
 	/**
 	 * Create an Address instance from a structured String with the form
-	 *
 	 * <pre class="code">
 	 * (exchange)/(routingKey)
 	 * </pre>
 	 * .
+	 * If exchange is parsed to empty string, then routing key is treated as a queue name.
 	 * @param address a structured string.
 	 */
 	public Address(String address) {
@@ -120,9 +123,9 @@ public boolean equals(Object o) {
 
 	@Override
 	public int hashCode() {
-		int result = this.exchangeName != null ? this.exchangeName.hashCode() : 0;
+		int result = this.exchangeName.hashCode();
 		int prime = 31; // NOSONAR magic #
-		result = prime * result + (this.routingKey != null ? this.routingKey.hashCode() : 0);
+		result = prime * result + this.routingKey.hashCode();
 		return result;
 	}
 

spring-rabbitmq-client/src/main/java/org/springframework/amqp/rabbitmq/client/RabbitAmqpUtils.java

@@ -19,6 +19,7 @@
 import java.nio.charset.StandardCharsets;
 import java.util.Date;
 import java.util.Map;
+import java.util.Objects;
 import java.util.UUID;
 
 import com.rabbitmq.client.amqp.Consumer;
@@ -72,8 +73,12 @@ public static Message fromAmqpMessage(com.rabbitmq.client.amqp.Message amqpMessa
 	}
 
 	/**
-	 * Convert {@link com.rabbitmq.client.amqp.Message} into {@link Message}.
-	 * @param amqpMessage the {@link com.rabbitmq.client.amqp.Message} convert from.
+	 * Convert {@link Message} into {@link com.rabbitmq.client.amqp.Message}.
+	 * The {@link MessageProperties#getReplyTo()} is set into {@link com.rabbitmq.client.amqp.Message#to(String)}.
+	 * The {@link com.rabbitmq.client.amqp.Message#correlationId(long)} is set to
+	 * {@link MessageProperties#getCorrelationId()} if present, or to {@link MessageProperties#getMessageId()}.
+	 * @param message the {@link Message} convert from.
+	 * @param amqpMessage the {@link com.rabbitmq.client.amqp.Message} convert into.
 	 */
 	public static void toAmqpMessage(Message message, com.rabbitmq.client.amqp.Message amqpMessage) {
 		MessageProperties messageProperties = message.getMessageProperties();
@@ -83,9 +88,11 @@ public static void toAmqpMessage(Message message, com.rabbitmq.client.amqp.Messa
 				.contentEncoding(messageProperties.getContentEncoding())
 				.contentType(messageProperties.getContentType())
 				.messageId(messageProperties.getMessageId())
-				.correlationId(messageProperties.getCorrelationId())
+				.correlationId(
+						Objects.requireNonNullElse(
+								messageProperties.getCorrelationId(), messageProperties.getMessageId()))
 				.priority(messageProperties.getPriority().byteValue())
-				.replyTo(messageProperties.getReplyTo());
+				.to(messageProperties.getReplyTo());
 
 		Map<String, @Nullable Object> headers = messageProperties.getHeaders();
 		if (!headers.isEmpty()) {

spring-rabbitmq-client/src/main/java/org/springframework/amqp/rabbitmq/client/listener/RabbitAmqpMessageListenerAdapter.java

@@ -120,7 +120,7 @@ public void onMessageBatch(List<Message> messages) {
 			InvocationResult result = getHandlerAdapter()
 					.invoke(converted, amqpAcknowledgment);
 			if (result.getReturnValue() != null) {
-				logger.warn("Replies are not currently supported with RabbitMQ AMQP 1.0 listeners");
+				logger.warn("Replies for batches are not currently supported with RabbitMQ AMQP 1.0 listeners");
 			}
 		}
 		catch (Exception ex) {