GH-2991: Extract AmqpConnectionFactory abstraction

Fixes: #2991

It turns out to be not very convenient when application fails on initialization due to not having connection with the broker.
So, the `AmqpConnectionFactoryBean` is wrong contract and better look into a `ConnectionFactory` abstraction instead.

* Rework `AmqpConnectionFactoryBean` with its eager real connection to the `AmqpConnectionFactory` contract and
`SingleAmqpConnectionFactory` implementation where real connection only happens when its `getConnection()` is called
* Rework all the client components to rely on the new `AmqpConnectionFactory` contract
* Make `Publisher` instantiation in a similar to `Connection` manner - on demand, when `RabbitAmqpTemplate` calls its internal `getPublisher()`

Author: artembilan

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

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2025 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.amqp.rabbitmq.client;
+
+import com.rabbitmq.client.amqp.Connection;
+
+/**
+ * The contract for RabbitMQ AMQP 1.0 {@link Connection} management.
+ *
+ * @author Artem Bilan
+ *
+ * @since 4.0
+ */
+public interface AmqpConnectionFactory {
+
+	Connection getConnection();
+
+}

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

@@ -25,7 +25,6 @@
 import java.util.concurrent.atomic.AtomicReference;
 
 import com.rabbitmq.client.amqp.AmqpException;
-import com.rabbitmq.client.amqp.Connection;
 import com.rabbitmq.client.amqp.Management;
 import org.jspecify.annotations.Nullable;
 
@@ -67,7 +66,7 @@ public class RabbitAmqpAdmin
 
 	public static final String QUEUE_TYPE = "QUEUE_TYPE";
 
-	private final Connection amqpConnection;
+	private final AmqpConnectionFactory connectionFactory;
 
 	private TaskExecutor taskExecutor = new SimpleAsyncTaskExecutor();
 
@@ -88,8 +87,8 @@ public class RabbitAmqpAdmin
 
 	private volatile boolean running = false;
 
-	public RabbitAmqpAdmin(Connection amqpConnection) {
-		this.amqpConnection = amqpConnection;
+	public RabbitAmqpAdmin(AmqpConnectionFactory connectionFactory) {
+		this.connectionFactory = connectionFactory;
 	}
 
 	@Override
@@ -231,7 +230,7 @@ private void declareDeclarableBeans() {
 			return;
 		}
 
-		try (Management management = this.amqpConnection.management()) {
+		try (Management management = getManagement()) {
 			exchanges.forEach((exchange) -> doDeclareExchange(management, exchange));
 			queues.forEach((queue) -> doDeclareQueue(management, queue));
 			bindings.forEach((binding) -> doDeclareBinding(management, binding));
@@ -273,7 +272,7 @@ private <T extends Declarable> boolean declarableByMe(T dec) {
 
 	@Override
 	public void declareExchange(Exchange exchange) {
-		try (Management management = this.amqpConnection.management()) {
+		try (Management management = getManagement()) {
 			doDeclareExchange(management, exchange);
 		}
 	}
@@ -307,15 +306,15 @@ public boolean deleteExchange(String exchangeName) {
 			return false;
 		}
 
-		try (Management management = this.amqpConnection.management()) {
+		try (Management management = getManagement()) {
 			management.exchangeDelete(exchangeName);
 		}
 		return true;
 	}
 
 	@Override
 	public @Nullable Queue declareQueue() {
-		try (Management management = this.amqpConnection.management()) {
+		try (Management management = getManagement()) {
 			return doDeclareQueue(management);
 		}
 	}
@@ -340,7 +339,7 @@ public boolean deleteExchange(String exchangeName) {
 
 	@Override
 	public @Nullable String declareQueue(Queue queue) {
-		try (Management management = this.amqpConnection.management()) {
+		try (Management management = getManagement()) {
 			return doDeclareQueue(management, queue);
 		}
 	}
@@ -378,7 +377,7 @@ public boolean deleteQueue(String queueName) {
 	@ManagedOperation(description =
 			"Delete a queue from the broker if unused and empty (when corresponding arguments are true")
 	public void deleteQueue(String queueName, boolean unused, boolean empty) {
-		try (Management management = this.amqpConnection.management()) {
+		try (Management management = getManagement()) {
 			Management.QueueInfo queueInfo = management.queueInfo(queueName);
 			if ((!unused || queueInfo.consumerCount() == 0)
 					&& (!empty || queueInfo.messageCount() == 0)) {
@@ -402,15 +401,15 @@ public void purgeQueue(String queueName, boolean noWait) {
 	@Override
 	@ManagedOperation(description = "Purge a queue and return the number of messages purged")
 	public int purgeQueue(String queueName) {
-		try (Management management = this.amqpConnection.management()) {
+		try (Management management = getManagement()) {
 			management.queuePurge(queueName);
 		}
 		return 0;
 	}
 
 	@Override
 	public void declareBinding(Binding binding) {
-		try (Management management = this.amqpConnection.management()) {
+		try (Management management = getManagement()) {
 			doDeclareBinding(management, binding);
 		}
 	}
@@ -441,7 +440,7 @@ public void removeBinding(Binding binding) {
 			return;
 		}
 
-		try (Management management = this.amqpConnection.management()) {
+		try (Management management = getManagement()) {
 			Management.UnbindSpecification unbindSpecification =
 					management.unbind()
 							.sourceExchange(binding.getExchange())
@@ -481,7 +480,7 @@ public void removeBinding(Binding binding) {
 
 	@Override
 	public @Nullable QueueInformation getQueueInfo(String queueName) {
-		try (Management management = this.amqpConnection.management()) {
+		try (Management management = getManagement()) {
 			Management.QueueInfo queueInfo = management.queueInfo(queueName);
 			QueueInformation queueInformation =
 					new QueueInformation(queueInfo.name(), queueInfo.messageCount(), queueInfo.consumerCount());
@@ -490,6 +489,10 @@ public void removeBinding(Binding binding) {
 		}
 	}
 
+	private Management getManagement() {
+		return this.connectionFactory.getConnection().management();
+	}
+
 	private <T extends Throwable> void logOrRethrowDeclarationException(@Nullable Declarable element,
 			String elementType, T t) throws T {
 
@@ -566,5 +569,4 @@ else if (declarable instanceof Binding binding) {
 		});
 	}
 
-
 }

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

@@ -19,12 +19,12 @@
 import java.time.Duration;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 
-import com.rabbitmq.client.amqp.Connection;
 import com.rabbitmq.client.amqp.Consumer;
 import com.rabbitmq.client.amqp.Environment;
 import com.rabbitmq.client.amqp.Publisher;
-import com.rabbitmq.client.amqp.PublisherBuilder;
 import com.rabbitmq.client.amqp.Resource;
 import org.jspecify.annotations.Nullable;
 
@@ -42,7 +42,6 @@
 import org.springframework.amqp.support.converter.SmartMessageConverter;
 import org.springframework.amqp.utils.JavaUtils;
 import org.springframework.beans.factory.DisposableBean;
-import org.springframework.beans.factory.InitializingBean;
 import org.springframework.core.ParameterizedTypeReference;
 import org.springframework.util.Assert;
 
@@ -54,14 +53,13 @@
  *
  * @since 4.0
  */
-public class RabbitAmqpTemplate implements AsyncAmqpTemplate, InitializingBean, DisposableBean {
+public class RabbitAmqpTemplate implements AsyncAmqpTemplate, DisposableBean {
 
-	private final Connection connection;
+	private final AmqpConnectionFactory connectionFactory;
 
-	private final PublisherBuilder publisherBuilder;
+	private final Lock instanceLock = new ReentrantLock();
 
-	@SuppressWarnings("NullAway.Init")
-	private Publisher publisher;
+	private @Nullable Object publisher;
 
 	private MessageConverter messageConverter = new SimpleMessageConverter();
 
@@ -73,17 +71,20 @@ public class RabbitAmqpTemplate implements AsyncAmqpTemplate, InitializingBean,
 
 	private @Nullable String defaultReceiveQueue;
 
-	public RabbitAmqpTemplate(Connection amqpConnection) {
-		this.connection = amqpConnection;
-		this.publisherBuilder = amqpConnection.publisherBuilder();
+	private Resource.StateListener @Nullable [] stateListeners;
+
+	private Duration publishTimeout = Duration.ofSeconds(60);
+
+	public RabbitAmqpTemplate(AmqpConnectionFactory connectionFactory) {
+		this.connectionFactory = connectionFactory;
 	}
 
 	public void setListeners(Resource.StateListener... listeners) {
-		this.publisherBuilder.listeners(listeners);
+		this.stateListeners = listeners;
 	}
 
 	public void setPublishTimeout(Duration timeout) {
-		this.publisherBuilder.publishTimeout(timeout);
+		this.publishTimeout = timeout;
 	}
 
 	/**
@@ -100,15 +101,15 @@ public void setExchange(String exchange) {
 	/**
 	 * Set a default routing key.
 	 * Mutually exclusive with {@link #setQueue(String)}.
-	 * @param key the default routing key.
+	 * @param routingKey the default routing key.
 	 */
-	public void setKey(String key) {
-		this.defaultRoutingKey = key;
+	public void setRoutingKey(String routingKey) {
+		this.defaultRoutingKey = routingKey;
 	}
 
 	/**
 	 * Set default queue for publishing.
-	 * Mutually exclusive with {@link #setExchange(String)} and {@link #setKey(String)}.
+	 * Mutually exclusive with {@link #setExchange(String)} and {@link #setRoutingKey(String)}.
 	 * @param queue the default queue.
 	 */
 	public void setQueue(String queue) {
@@ -137,14 +138,36 @@ private String getRequiredQueue() throws IllegalStateException {
 		return name;
 	}
 
-	@Override
-	public void afterPropertiesSet() {
-		this.publisher = this.publisherBuilder.build();
+	private Publisher getPublisher() {
+		Object publisherToReturn = this.publisher;
+		if (publisherToReturn == null) {
+			this.instanceLock.lock();
+			try {
+				publisherToReturn = this.publisher;
+				if (publisherToReturn == null) {
+					publisherToReturn =
+							this.connectionFactory.getConnection()
+									.publisherBuilder()
+									.listeners(this.stateListeners)
+									.publishTimeout(this.publishTimeout)
+									.build();
+					this.publisher = publisherToReturn;
+				}
+			}
+			finally {
+				this.instanceLock.unlock();
+			}
+		}
+		return (Publisher) publisherToReturn;
 	}
 
 	@Override
 	public void destroy() {
-		this.publisher.close();
+		Object publisherToClose = this.publisher;
+		if (publisherToClose != null) {
+			((Publisher) publisherToClose).close();
+			this.publisher = null;
+		}
 	}
 
 	/**
@@ -178,7 +201,7 @@ public CompletableFuture<Boolean> send(String exchange, @Nullable String routing
 	private CompletableFuture<Boolean> doSend(@Nullable String exchange, @Nullable String routingKey,
 			@Nullable String queue, Message message) {
 
-		com.rabbitmq.client.amqp.Message amqpMessage = this.publisher.message();
+		com.rabbitmq.client.amqp.Message amqpMessage = getPublisher().message();
 		com.rabbitmq.client.amqp.Message.MessageAddressBuilder address = amqpMessage.toAddress();
 		JavaUtils.INSTANCE
 				.acceptIfNotNull(exchange, address::exchange)
@@ -191,7 +214,7 @@ private CompletableFuture<Boolean> doSend(@Nullable String exchange, @Nullable S
 
 		CompletableFuture<Boolean> publishResult = new CompletableFuture<>();
 
-		this.publisher.publish(amqpMessage,
+		getPublisher().publish(amqpMessage,
 				(context) -> {
 					switch (context.status()) {
 						case ACCEPTED -> publishResult.complete(true);
@@ -271,7 +294,8 @@ public CompletableFuture<Message> receive(String queueName) {
 		CompletableFuture<Message> messageFuture = new CompletableFuture<>();
 
 		Consumer consumer =
-				this.connection.consumerBuilder()
+				this.connectionFactory.getConnection()
+						.consumerBuilder()
 						.queue(queueName)
 						.initialCredits(1)
 						.priority(10)