11. AMQP Support

11. AMQP Support
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11.1 Introduction

Spring Integration provides Channel Adapters for receiving and sending messages using the Advanced Message Queuing Protocol (AMQP). The following adapters are available:

Spring Integration also provides a point-to-point Message Channel as well as a publish/subscribe Message Channel backed by AMQP Exchanges and Queues.

In order to provide AMQP support, Spring Integration relies on (Spring AMQP) which "applies core Spring concepts to the development of AMQP-based messaging solutions". Spring AMQP provides similar semantics to (Spring JMS).

Whereas the provided AMQP Channel Adapters are intended for unidirectional Messaging (send or receive) only, Spring Integration also provides inbound and outbound AMQP Gateways for request/reply operations.

	Tip
	Please familiarize yourself with the reference documentation of the Spring AMQP project as well. It provides much more in-depth information regarding Spring’s integration with AMQP in general and RabbitMQ in particular.

11.2 Inbound Channel Adapter

A configuration sample for an AMQP Inbound Channel Adapter is shown below.

<int-amqp:inbound-channel-adapter
                                  id="inboundAmqp" 
                                  channel="inboundChannel" 
                                  queue-names="si.test.queue" 
                                  acknowledge-mode="AUTO" 
                                  advice-chain="" 
                                  channel-transacted="" 
                                  concurrent-consumers="" 
                                  connection-factory="" 
                                  error-channel="" 
                                  expose-listener-channel="" 
                                  header-mapper="" 
                                  mapped-request-headers="" 
                                  listener-container="" 
                                  message-converter="" 
                                  message-properties-converter="" 
                                  phase="" (16)
                                  prefetch-count="" (17)
                                  receive-timeout="" (18)
                                  recovery-interval="" (19)
                                  missing-queues-fatal="" (20)
                                  shutdown-timeout="" (21)
                                  task-executor="" (22)
                                  transaction-attribute="" (23)
                                  transaction-manager="" (24)
                                  tx-size="" /> (25)

	Unique ID for this adapter. Optional.
	Message Channel to which converted Messages should be sent. Required.
	Names of the AMQP Queues from which Messages should be consumed (comma-separated list).Required.
	Acknowledge Mode for the `MessageListenerContainer`. When set to MANUAL, the delivery tag and channel are provided in message headers `amqp_deliveryTag` and `amqp_channel` respectively; the user application is responsible for acknowledgement. NONE means no acknowledgements (autoAck); AUTO means the adapter’s container will acknowledge when the downstream flow completes.Optional (Defaults to AUTO) see Section 11.4, “Inbound Endpoint Acknowledge Mode”.
	Extra AOP Advice(s) to handle cross cutting behavior associated with this Inbound Channel Adapter. Optional.
	Flag to indicate that channels created by this component will be transactional. If true, tells the framework to use a transactional channel and to end all operations (send or receive) with a commit or rollback depending on the outcome, with an exception signalling a rollback. Optional (Defaults to false).
	Specify the number of concurrent consumers to create. Default is 1. Raising the number of concurrent consumers is recommended in order to scale the consumption of messages coming in from a queue. However, note that any ordering guarantees are lost once multiple consumers are registered. In general, stick with 1 consumer for low-volume queues. Optional.
	Bean reference to the RabbitMQ ConnectionFactory. Optional (Defaults to connectionFactory).
	Message Channel to which error Messages should be sent. Optional.
	Shall the listener channel (com.rabbitmq.client.Channel) be exposed to a registered `ChannelAwareMessageListener`. Optional (Defaults to true).
	A reference to an `AmqpHeaderMapper` to use when receiving AMQP Messages. Optional. By default only standard AMQP properties (e.g. `contentType`) will be copied to Spring Integration `MessageHeaders`. Any user-defined headers within the AMQP `MessageProperties` will NOT be copied to the Message by the default `DefaultAmqpHeaderMapper`. Not allowed if request-header-names is provided.
	Comma-separated list of names of AMQP Headers to be mapped from the AMQP request into the MessageHeaders. This can only be provided if the header-mapper reference is not provided. The values in this list can also be simple patterns to be matched against the header names (e.g. "" or "foo, bar" or "*foo").
	Reference to the `SimpleMessageListenerContainer` to use for receiving AMQP Messages. If this attribute is provided, then no other attribute related to the listener container configuration should be provided. In other words, by setting this reference, you must take full responsibility of the listener container configuration. The only exception is the MessageListener itself. Since that is actually the core responsibility of this Channel Adapter implementation, the referenced listener container must NOT already have its own MessageListener configured. Optional.
	The MessageConverter to use when receiving AMQP Messages. Optional.
	The MessagePropertiesConverter to use when receiving AMQP Messages. Optional.
(16)	Specify the phase in which the underlying `SimpleMessageListenerContainer` should be started and stopped. The startup order proceeds from lowest to highest, and the shutdown order is the reverse of that. By default this value is Integer.MAX_VALUE meaning that this container starts as late as possible and stops as soon as possible. Optional.
(17)	Tells the AMQP broker how many messages to send to each consumer in a single request. Often this can be set quite high to improve throughput. It should be greater than or equal to the transaction size (see attribute "tx-size"). Optional (Defaults to 1).
(18)	Receive timeout in milliseconds. Optional (Defaults to 1000).
(19)	Specifies the interval between recovery attempts of the underlying `SimpleMessageListenerContainer` (in milliseconds) .Optional (Defaults to 5000).
(20)	If true, and none of the queues are available on the broker, the container will throw a fatal exception during startup and will stop if the queues are deleted when the container is running (after making 3 attempts to passively declare the queues). If false, the container will not throw an exception and go into recovery mode, attempting to restart according to the `recovery-interval`. Optional (Defaults to `true`).
(21)	The time to wait for workers in milliseconds after the underlying `SimpleMessageListenerContainer` is stopped, and before the AMQP connection is forced closed. If any workers are active when the shutdown signal comes they will be allowed to finish processing as long as they can finish within this timeout. Otherwise the connection is closed and messages remain unacked (if the channel is transactional). Optional (Defaults to 5000).
(22)	By default, the underlying `SimpleMessageListenerContainer` uses a SimpleAsyncTaskExecutor implementation, that fires up a new Thread for each task, executing it asynchronously. By default, the number of concurrent threads is unlimited. NOTE: This implementation does not reuse threads. Consider a thread-pooling TaskExecutor implementation as an alternative. Optional (Defaults to SimpleAsyncTaskExecutor).
(23)	By default the underlying `SimpleMessageListenerContainer` creates a new instance of the DefaultTransactionAttribute (takes the EJB approach to rolling back on runtime, but not checked exceptions. Optional (Defaults to DefaultTransactionAttribute).
(24)	Sets a Bean reference to an external `PlatformTransactionManager` on the underlying SimpleMessageListenerContainer. The transaction manager works in conjunction with the "channel-transacted" attribute. If there is already a transaction in progress when the framework is sending or receiving a message, and the channelTransacted flag is true, then the commit or rollback of the messaging transaction will be deferred until the end of the current transaction. If the channelTransacted flag is false, then no transaction semantics apply to the messaging operation (it is auto-acked). For further information see Transactions with Spring AMQP. Optional.
(25)	Tells the `SimpleMessageListenerContainer` how many messages to process in a single transaction (if the channel is transactional). For best results it should be less than or equal to the set "prefetch-count". Optional (Defaults to 1).

container

	container
Note that when configuring an external container, you cannot use the Spring AMQP namespace to define the container. This is because the namespace requires at least one `<listener/>` element. In this environment, the listener is internal to the adapter. For this reason, you must define the container using a normal Spring `<bean/>` definition, such as: <bean id="container" class="org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer"> <property name="connectionFactory" ref="connectionFactory" /> <property name="queueNames" value="foo.queue" /> <property name="defaultRequeueRejected" value="false"/> </bean>

Note that when configuring an external container, you cannot use the Spring AMQP namespace to define the container. This is because the namespace requires at least one <listener/> element. In this environment, the listener is internal to the adapter. For this reason, you must define the container using a normal Spring <bean/> definition, such as:

<bean id="container"
 class="org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer">
    <property name="connectionFactory" ref="connectionFactory" />
    <property name="queueNames" value="foo.queue" />
    <property name="defaultRequeueRejected" value="false"/>
</bean>

Important

Even though the Spring Integration JMS and AMQP support is very similar, important differences exist. The JMS Inbound Channel Adapter is using a JmsDestinationPollingSource under the covers and expects a configured Poller. The AMQP Inbound Channel Adapter on the other side uses a`SimpleMessageListenerContainer` and is message driven. In that regard it is more similar to the JMS Message Driven Channel Adapter.

11.2.1 Configuring with Java Configuration

The following Spring Boot application provides an example of configuring the inbound adapter using Java configuration:

@SpringBootApplication
public class AmqpJavaApplication {

    public static void main(String[] args) {
        new SpringApplicationBuilder(AmqpJavaApplication.class)
            .web(false)
            .run(args);
    }

    @Bean
    public MessageChannel amqpInputChannel() {
        return new DirectChannel();
    }

    @Bean
    public AmqpInboundChannelAdapter inbound(SimpleMessageListenerContainer listenerContainer,
            @Qualifier("amqpInputChannel") MessageChannel channel) {
        AmqpInboundChannelAdapter adapter = new AmqpInboundChannelAdapter(listenerContainer);
        adapter.setOutputChannel(channel);
        return adapter;
    }

    @Bean
    public SimpleMessageListenerContainer container(ConnectionFactory connectionFactory) {
        SimpleMessageListenerContainer container =
                                   new SimpleMessageListenerContainer(connectionFactory);
        container.setQueueNames("foo");
        container.setConcurrentConsumers(2);
        // ...
        return container;
    }

    @Bean
    @ServiceActivator(inputChannel = "amqpInputChannel")
    public MessageHandler handler() {
        return new MessageHandler() {

            @Override
            public void handleMessage(Message<?> message) throws MessagingException {
                System.out.println(message.getPayload());
            }

        };
    }

}

11.2.2 Configuring with the Java DSL

The following Spring Boot application provides an example of configuring the inbound adapter using the Java DSL:

@SpringBootApplication
public class AmqpJavaApplication {

    public static void main(String[] args) {
        new SpringApplicationBuilder(AmqpJavaApplication.class)
            .web(false)
            .run(args);
    }

    @Bean
    public IntegrationFlow amqpInbound(ConnectionFactory connectionFactory) {
        return IntegrationFlows.from(Amqp.inboundAdapter(connectionFactory, "foo"))
                .handle(m -> System.out.println(m.getPayload()))
                .get();
    }

}

11.3 Inbound Gateway

The inbound gateway supports all the attributes on the inbound channel adapter (except channel is replaced by request-channel), plus some additional attributes:

<int-amqp:inbound-gateway
                          id="inboundGateway" 
                          request-channel="myRequestChannel" 
                          header-mapper="" 
                          mapped-request-headers="" 
                          mapped-reply-headers="" 
                          reply-channel="myReplyChannel" 
                          reply-timeout="1000"  
                          amqp-template="" 
                          default-reply-to="" />

	Unique ID for this adapter. Optional.
	Message Channel to which converted Messages should be sent. Required.
	A reference to an `AmqpHeaderMapper` to use when receiving AMQP Messages. Optional. By default only standard AMQP properties (e.g. `contentType`) will be copied to and from Spring Integration `MessageHeaders`. Any user-defined headers within the AMQP`MessageProperties` will NOT be copied to or from an AMQP Message by the default `DefaultAmqpHeaderMapper`. Not allowed if request-header-names or reply-header-names is provided.
	Comma-separated list of names of AMQP Headers to be mapped from the AMQP request into the `MessageHeaders`. This can only be provided if the header-mapper reference is not provided. The values in this list can also be simple patterns to be matched against the header names (e.g. "" or "foo, bar" or "*foo").
	Comma-separated list of names of `MessageHeaders` to be mapped into the AMQP Message Properties of the AMQP reply message. All standard Headers (e.g., `contentType`) will be mapped to AMQP Message Properties while user-defined headers will be mapped to the headers property. This can only be provided if the header-mapper reference is not provided. The values in this list can also be simple patterns to be matched against the header names (e.g. "" or "foo, bar" or "*foo").
	Message Channel where reply Messages will be expected. Optional.
	Used to set the `receiveTimeout` on the underlying `org.springframework.integration.core.MessagingTemplate` for receiving messages from the reply channel. If not specified this property will default to "1000" (1 second). Only applies if the container thread hands off to another thread before the reply is sent.
	The customized `AmqpTemplate` bean reference to have more control for the reply messages to send or you can provide an alternative implementation to the `RabbitTemplate`.
	The `replyTo` `org.springframework.amqp.core.Address` to be used when the `requestMessage` doesn’t have `replyTo` property. If this option isn’t specified, no `amqp-template` is provided, and no `replyTo` property exists in the request message, an `IllegalStateException` is thrown because the reply can’t be routed. If this option isn’t specified, and an external `amqp-template` is provided, no exception will be thrown. You must either specify this option, or configure a default `exchange` and `routingKey` on that template, if you anticipate cases when no `replyTo` property exists in the request message.

See the note in Section 11.2, “Inbound Channel Adapter” about configuring the listener-container attribute.

11.3.1 Configuring with Java Configuration

The following Spring Boot application provides an example of configuring the inbound gateway using Java configuration:

@SpringBootApplication
public class AmqpJavaApplication {

    public static void main(String[] args) {
        new SpringApplicationBuilder(AmqpJavaApplication.class)
            .web(false)
            .run(args);
    }

    @Bean
    public MessageChannel amqpInputChannel() {
        return new DirectChannel();
    }

    @Bean
    public AmqpInboundGateway inbound(SimpleMessageListenerContainer listenerContainer,
            @Qualifier("amqpInputChannel") MessageChannel channel) {
        AmqpInboundGateway gateway = new AmqpInboundGateway(listenerContainer);
        gateway.setRequestChannel(channel);
        gateway.setDefaultReplyTo("bar");
        return gateway;
    }

    @Bean
    public SimpleMessageListenerContainer container(ConnectionFactory connectionFactory) {
        SimpleMessageListenerContainer container =
                        new SimpleMessageListenerContainer(connectionFactory);
        container.setQueueNames("foo");
        container.setConcurrentConsumers(2);
        // ...
        return container;
    }

    @Bean
    @ServiceActivator(inputChannel = "amqpInputChannel")
    public MessageHandler handler() {
        return new AbstractReplyProducingMessageHandler() {

            @Override
            protected Object handleRequestMessage(Message<?> requestMessage) {
                return "reply to " + requestMessage.getPayload();
            }

        };
    }

}

11.3.2 Configuring with the Java DSL

The following Spring Boot application provides an example of configuring the inbound gateway using the Java DSL:

@SpringBootApplication
public class AmqpJavaApplication {

    public static void main(String[] args) {
        new SpringApplicationBuilder(AmqpJavaApplication.class)
            .web(false)
            .run(args);
    }

    @Bean // return the upper cased payload
    public IntegrationFlow amqpInboundGateway(ConnectionFactory connectionFactory) {
        return IntegrationFlows.from(Amqp.inboundGateway(connectionFactory, "foo"))
                .transform(String.class, String::toUpperCase)
                .get();
    }

}

11.4 Inbound Endpoint Acknowledge Mode

By default the inbound endpoints use acknowledge mode AUTO, which means the container automatically acks the message when the downstream integration flow completes (or a message is handed off to another thread using a QueueChannel or ExecutorChannel). Setting the mode to NONE configures the consumer such that acks are not used at all (the broker automatically acks the message as soon as it is sent). Setting the mode to`MANUAL` allows user code to ack the message at some other point during processing. To support this, with this mode, the endpoints provide the Channel and deliveryTag in the amqp_channel and amqp_deliveryTag headers respectively.

You can perform any valid rabbit command on the Channel but, generally, only basicAck and basicNack (or basicReject) would be used. In order to not interfere with the operation of the container, you should not retain a reference to the channel and just use it in the context of the current message.

	Note
	Since the `Channel` is a reference to a "live" object, it cannot be serialized and will be lost if a message is persisted.

This is an example of how you might use MANUAL acknowledgement:

@ServiceActivator(inputChannel = "foo", outputChannel = "bar")
public Object handle(@Payload String payload, @Header(AmqpHeaders.CHANNEL) Channel channel,
        @Header(AmqpHeaders.DELIVERY_TAG) Long deliveryTag) throws Exception {

    // Do some processing

    if (allOK) {
        channel.basicAck(deliveryTag, false);

        // perhaps do some more processing

    }
    else {
        channel.basicNack(deliveryTag, false, true);
    }
    return someResultForDownStreamProcessing;
}

11.5 Outbound Channel Adapter

A configuration sample for an AMQP Outbound Channel Adapter is shown below.

<int-amqp:outbound-channel-adapter id="outboundAmqp" 
                               channel="outboundChannel" 
                               amqp-template="myAmqpTemplate" 
                               exchange-name="" 
                               exchange-name-expression="" 
                               order="1" 
                               routing-key="" 
                               routing-key-expression="" 
                               default-delivery-mode"" 
                               confirm-correlation-expression="" 
                               confirm-ack-channel="" 
                               confirm-nack-channel="" 
                               return-channel="" 
                               header-mapper="" 
                               mapped-request-headers="" 
                               lazy-connect="true" /> (16)

	Unique ID for this adapter. Optional.
	Message Channel to which Messages should be sent in order to have them converted and published to an AMQP Exchange. Required.
	Bean Reference to the configured AMQP Template Optional (Defaults to "amqpTemplate").
	The name of the AMQP Exchange to which Messages should be sent. If not provided, Messages will be sent to the default, no-name Exchange. Mutually exclusive with exchange-name-expression. Optional.
	A SpEL expression that is evaluated to determine the name of the AMQP Exchange to which Messages should be sent, with the message as the root object. If not provided, Messages will be sent to the default, no-name Exchange. Mutually exclusive with exchange-name. Optional.
	The order for this consumer when multiple consumers are registered thereby enabling load- balancing and/or failover. Optional (Defaults to Ordered.LOWEST_PRECEDENCE [=Integer.MAX_VALUE]).
	The fixed routing-key to use when sending Messages. By default, this will be an empty String. Mutually exclusive with routing-key-expression.Optional.
	A SpEL expression that is evaluated to determine the routing-key to use when sending Messages, with the message as the root object (e.g. payload.key). By default, this will be an empty String. Mutually exclusive with routing-key. Optional.
	The default delivery mode for messages; PERSISTENT or NON_PERSISTENT. Overridden if the header-mapper sets the delivery mode. The DefaultHeaderMapper sets the value if the Spring Integration message header `amqp_deliveryMode` is present. If this attribute is not supplied and the header mapper doesn’t set it, the default depends on the underlying spring-amqp MessagePropertiesConverter used by the RabbitTemplate. If that is not customized at all, the default is PERSISTENT. Optional.
	An expression defining correlation data. When provided, this configures the underlying amqp template to receive publisher confirms. Requires a dedicated `RabbitTemplate` and a `CachingConnectionFactory` with the `publisherConfirms` property set to `true`. When a publisher confirm is received, and correlation data is supplied, it is written to either the confirm-ack-channel, or the confirm-nack-channel, depending on the confirmation type. The payload of the confirm is the correlation data as defined by this expression and the message will have a header amqp_publishConfirm set to true (ack) or false (nack). Examples: "`headers['myCorrelationData']`", "`payload`". Starting with version 4.1 the `amqp_publishConfirmNackCause` message header has been added. It contains the `cause` of a nack for publisher confirms. Starting with version 4.2, if the expression resolves to a `Message<?>` instance (such as "`#this`"), the message emitted on the ack/nack channel is based on that message, with the additional header(s) added. Previously, a new message was created with the correlation data as its payload, regardless of type. Optional.
	The channel to which positive (ack) publisher confirms are sent; payload is the correlation data defined by the confirm-correlation-expression. Optional, default=nullChannel.
	The channel to which negative (nack) publisher confirms are sent; payload is the correlation data defined by the confirm-correlation-expression. Optional, default=nullChannel.
	The channel to which returned messages are sent. When provided, the underlying amqp template is configured to return undeliverable messages to the adapter. The message will be constructed from the data received from amqp, with the following additional headers: amqp_returnReplyCode, amqp_returnReplyText, amqp_returnExchange, amqp_returnRoutingKey. Optional.
	A reference to an `AmqpHeaderMapper` to use when sending AMQP Messages. By default only standard AMQP properties (e.g. `contentType`) will be copied to the Spring Integration `MessageHeaders`. Any user-defined headers will NOT be copied to the Message by the default`DefaultAmqpHeaderMapper`. Not allowed if request-header-names is provided. Optional.
	Comma-separated list of names of AMQP Headers to be mapped from the `MessageHeaders` to the AMQP Message. Not allowed if the header-mapper reference is provided. The values in this list can also be simple patterns to be matched against the header names (e.g. "" or "foo, bar" or "*foo").
(16)	When set to `false`, the endpoint will attempt to connect to the broker during application context initialization. This allows "fail fast" detection of bad configuration, but will also cause initialization to fail if the broker is down. When true (default), the connection is established (if it doesn’t already exist because some other component established it) when the first message is sent.

	return-channel
	Using a `return-channel` requires a `RabbitTemplate` with the `mandatory` property set to `true`, and a `CachingConnectionFactory` with the `publisherReturns` property set to `true`. When using multiple outbound endpoints with returns, a separate `RabbitTemplate` is needed for each endpoint.

11.5.1 Configuring with Java Configuration

The following Spring Boot application provides an example of configuring the outbound adapter using Java configuration:

@SpringBootApplication
@IntegrationComponentScan
public class AmqpJavaApplication {

    public static void main(String[] args) {
         ConfigurableApplicationContext context =
              new SpringApplicationBuilder(AmqpJavaApplication.class)
                       .web(false)
                       .run(args);
         MyGateway gateway = context.getBean(MyGateway.class);
         gateway.sendToRabbit("foo");
    }

    @Bean
    @ServiceActivator(inputChannel = "amqpOutboundChannel")
    public AmqpOutboundEndpoint amqpOutbound(AmqpTemplate amqpTemplate) {
        AmqpOutboundEndpoint outbound = new AmqpOutboundEndpoint(amqpTemplate);
        outbound.setRoutingKey("foo"); // default exchange - route to queue 'foo'
        return outbound;
    }

    @Bean
    public MessageChannel amqpOutboundChannel() {
        return new DirectChannel();
    }

    @MessagingGateway(defaultRequestChannel = "amqpOutboundChannel")
    public interface MyGateway {

        void sendToRabbit(String data);

    }

}

11.5.2 Configuring with the Java DSL

The following Spring Boot application provides an example of configuring the outbound adapter using the Java DSL:

@SpringBootApplication
@IntegrationComponentScan
public class AmqpJavaApplication {

    public static void main(String[] args) {
         ConfigurableApplicationContext context =
                  new SpringApplicationBuilder(AmqpJavaApplication.class)
                          .web(false)
                          .run(args);
         MyGateway gateway = context.getBean(MyGateway.class);
         gateway.sendToRabbit("foo");
    }

    @Bean
    public IntegrationFlow amqpOutbound(AmqpTemplate amqpTemplate) {
        return IntegrationFlows.from(amqpOutboundChannel())
                .handle(Amqp.outboundAdapter(amqpTemplate)
                            .routingKey("foo")) // default exchange - route to queue 'foo'
                .get();
    }

    @Bean
    public MessageChannel amqpOutboundChannel() {
        return new DirectChannel();
    }

    @MessagingGateway(defaultRequestChannel = "amqpOutboundChannel")
    public interface MyGateway {

        void sendToRabbit(String data);

    }
}

11.6 Outbound Gateway

A configuration sample for an AMQP Outbound Gateway is shown below.

<int-amqp:outbound-gateway id="inboundGateway" 
                           request-channel="myRequestChannel" 
                           amqp-template="" 
                           exchange-name="" 
                           exchange-name-expression="" 
                           order="1" 
                           reply-channel="" 
                           reply-timeout="" 
                           requires-reply="" 
                           routing-key="" 
                           routing-key-expression="" 
                           default-delivery-mode"" 
                           confirm-correlation-expression="" 
                           confirm-ack-channel="" 
                           confirm-nack-channel="" 
                           return-channel="" (16)
                           lazy-connect="true" /> (17)

	Unique ID for this adapter. Optional.
	Message Channel to which Messages should be sent in order to have them converted and published to an AMQP Exchange. Required.
	Bean Reference to the configured AMQP Template Optional (Defaults to "amqpTemplate").
	The name of the AMQP Exchange to which Messages should be sent. If not provided, Messages will be sent to the default, no-name Exchange. Mutually exclusive with exchange-name-expression. Optional.
	A SpEL expression that is evaluated to determine the name of the AMQP Exchange to which Messages should be sent, with the message as the root object. If not provided, Messages will be sent to the default, no-name Exchange. Mutually exclusive with exchange-name. Optional.
	The order for this consumer when multiple consumers are registered thereby enabling load- balancing and/or failover. Optional (Defaults to Ordered.LOWEST_PRECEDENCE [=Integer.MAX_VALUE]).
	Message Channel to which replies should be sent after being received from an AQMP Queue and converted.Optional.
	The time the gateway will wait when sending the reply message to the `reply-channel`. This only applies if the `reply-channel` can block - such as a `QueueChannel` with a capacity limit that is currently full. Default: infinity.
	When `true`, the gateway will throw an exception if no reply message is received within the `AmqpTemplate`'s `replyTimeout` property. Default: `true`.
	The routing-key to use when sending Messages. By default, this will be an empty String. Mutually exclusive with routing-key-expression. Optional.
	A SpEL expression that is evaluated to determine the routing-key to use when sending Messages, with the message as the root object (e.g. payload.key). By default, this will be an empty String. Mutually exclusive with routing-key. Optional.
	The default delivery mode for messages; PERSISTENT or NON_PERSISTENT. Overridden if the header-mapper sets the delivery mode. The DefaultHeaderMapper sets the value if the Spring Integration message header `amqp_deliveryMode` is present. If this attribute is not supplied and the header mapper doesn’t set it, the default depends on the underlying spring-amqp MessagePropertiesConverter used by the RabbitTemplate. If that is not customized at all, the default is PERSISTENT. Optional.
	Since version 4.2. An expression defining correlation data. When provided, this configures the underlying amqp template to receive publisher confirms. Requires a dedicated `RabbitTemplate` and a `CachingConnectionFactory` with the `publisherConfirms` property set to `true`. When a publisher confirm is received, and correlation data is supplied, it is written to either the confirm-ack-channel, or the confirm-nack-channel, depending on the confirmation type. The payload of the confirm is the correlation data as defined by this expression and the message will have a header amqp_publishConfirm set to true (ack) or false (nack). For nacks, an additional header `amqp_publishConfirmNackCause` is provided. Examples: "headers[myCorrelationData]", "payload". If the expression resolves to a `Message<?>` instance (such as "`#this`"), the message emitted on the ack/nack channel is based on that message, with the additional header(s) added. Previously, a new message was created with the correlation data as its payload, regardless of type. Optional.
	Since version 4.2. The channel to which positive (ack) publisher confirms are sent; payload is the correlation data defined by the confirm-correlation-expression. Optional, default=nullChannel.
	Since version 4.2. The channel to which negative (nack) publisher confirms are sent; payload is the correlation data defined by the confirm-correlation-expression. Optional, default=nullChannel.
(16)	The channel to which returned messages are sent. When provided, the underlying amqp template is configured to return undeliverable messages to the gateway. The message will be constructed from the data received from amqp, with the following additional headers: amqp_returnReplyCode, amqp_returnReplyText, amqp_returnExchange, amqp_returnRoutingKey. Optional.
(17)	When set to `false`, the endpoint will attempt to connect to the broker during application context initialization. This allows "fail fast" detection of bad configuration, but will also cause initialization to fail if the broker is down. When true (default), the connection is established (if it doesn’t already exist because some other component established it) when the first message is sent.

	return-channel
	Using a `return-channel` requires a `RabbitTemplate` with the `mandatory` property set to `true`, and a `CachingConnectionFactory` with the `publisherReturns` property set to `true`. When using multiple outbound endpoints with returns, a separate `RabbitTemplate` is needed for each endpoint.

	Important
	The underlying `AmqpTemplate` has a default `replyTimeout` of 5 seconds. If you require a longer timeout, it must be configured on the `template`.

11.6.1 Configuring with Java Configuration

The following Spring Boot application provides an example of configuring the outbound gateway using Java configuration:

@SpringBootApplication
@IntegrationComponentScan
public class AmqpJavaApplication {

    public static void main(String[] args) {
         ConfigurableApplicationContext context =
                new SpringApplicationBuilder(AmqpJavaApplication.class)
                       .web(false)
                       .run(args);
         MyGateway gateway = context.getBean(MyGateway.class);
         String reply = gateway.sendToRabbit("foo");
         System.out.println(reply);
    }

    @Bean
    @ServiceActivator(inputChannel = "amqpOutboundChannel")
    public AmqpOutboundEndpoint amqpOutbound(AmqpTemplate amqpTemplate) {
        AmqpOutboundEndpoint outbound = new AmqpOutboundEndpoint(amqpTemplate);
        outbound.setExpectReply(true);
        outbound.setRoutingKey("foo"); // default exchange - route to queue 'foo'
        return outbound;
    }

    @Bean
    public MessageChannel amqpOutboundChannel() {
        return new DirectChannel();
    }

    @MessagingGateway(defaultRequestChannel = "amqpOutboundChannel")
    public interface MyGateway {

        String sendToRabbit(String data);

    }

}

Notice that the only difference between the outbound adapter and outbound gateway configuration is the setting of the expectReply property.

11.6.2 Configuring with the Java DSL

The following Spring Boot application provides an example of configuring the outbound adapter using the Java DSL:

@SpringBootApplication
@IntegrationComponentScan
public class AmqpJavaApplication {

    public static void main(String[] args) {
         ConfigurableApplicationContext context =
                 new SpringApplicationBuilder(AmqpJavaApplication.class)
                      .web(false)
                      .run(args);
         RabbitTemplate template = context.getBean(RabbitTemplate.class);
         MyGateway gateway = context.getBean(MyGateway.class);
         String reply = gateway.sendToRabbit("foo");
         System.out.println(reply);
    }

    @Bean
    public IntegrationFlow amqpOutbound(AmqpTemplate amqpTemplate) {
        return IntegrationFlows.from(amqpOutboundChannel())
                .handle(Amqp.outboundGateway(amqpTemplate)
                        .routingKey("foo")) // default exchange - route to queue 'foo'
                .get();
    }

    @Bean
    public MessageChannel amqpOutboundChannel() {
        return new DirectChannel();
    }

    @MessagingGateway(defaultRequestChannel = "amqpOutboundChannel")
    public interface MyGateway {

        String sendToRabbit(String data);

    }
}

11.7 AMQP Backed Message Channels

There are two Message Channel implementations available. One is point-to-point, and the other is publish/subscribe. Both of these channels provide a wide range of configuration attributes for the underlying AmqpTemplate and SimpleMessageListenerContainer as you have seen on the Channel Adapters and Gateways. However, the examples we’ll show here are going to have minimal configuration. Explore the XML schema to view the available attributes.

A point-to-point channel would look like this:

<int-amqp:channel id="p2pChannel"/>

Under the covers a Queue named "si.p2pChannel" would be declared, and this channel will send to that Queue (technically by sending to the no-name Direct Exchange with a routing key that matches this Queue’s name). This channel will also register a consumer on that Queue. If for some reason, you want the Queue to be "pollable" instead of message-driven, then simply provide the "message-driven" flag with a value of false:

<int-amqp:channel id="p2pPollableChannel"  message-driven="false"/>

A publish/subscribe channel would look like this:

<int-amqp:publish-subscribe-channel id="pubSubChannel"/>

Under the covers a Fanout Exchange named "si.fanout.pubSubChannel" would be declared, and this channel will send to that Fanout Exchange. This channel will also declare a server-named exclusive, auto-delete, non-durable Queue and bind that to the Fanout Exchange while registering a consumer on that Queue to receive Messages. There is no "pollable" option for a publish-subscribe-channel; it must be message-driven.

Starting with version 4.1 AMQP Backed Message Channels, alongside with channel-transacted, support template-channel-transacted to separate transactional configuration for the AbstractMessageListenerContainer and for the RabbitTemplate. Note, previously, the channel-transacted was true by default, now it changed to false as standard default value for the AbstractMessageListenerContainer.

11.7.1 Configuring with Java Configuration

The following provides an example of configuring the channels using Java configuration:

@Bean
public AmqpChannelFactoryBean pollable(ConnectionFactory connectionFactory) {
    AmqpChannelFactoryBean factoryBean = new AmqpChannelFactoryBean();
    factoryBean.setConnectionFactory(connectionFactory);
    factoryBean.setQueueName("foo");
    factoryBean.setPubSub(false);
    return factoryBean;
}

@Bean
public AmqpChannelFactoryBean messageDriven(ConnectionFactory connectionFactory) {
    AmqpChannelFactoryBean factoryBean = new AmqpChannelFactoryBean(true);
    factoryBean.setConnectionFactory(connectionFactory);
    factoryBean.setQueueName("bar");
    factoryBean.setPubSub(false);
    return factoryBean;
}

@Bean
public AmqpChannelFactoryBean pubSub(ConnectionFactory connectionFactory) {
    AmqpChannelFactoryBean factoryBean = new AmqpChannelFactoryBean(true);
    factoryBean.setConnectionFactory(connectionFactory);
    factoryBean.setQueueName("baz");
    factoryBean.setPubSub(false);
    return factoryBean;
}

11.7.2 Configuring with the Java DSL

The following provides an example of configuring the channels using the Java DSL:

@Bean
public IntegrationFlow pollableInFlow(ConnectionFactory connectionFactory) {
    return IntegrationFlows.from(...)
            ...
            .channel(Amqp.pollableChannel(connectionFactory)
                    .queueName("foo"))
            ...
            .get();
}

@Bean
public IntegrationFlow messageDrivenInFow(ConnectionFactory connectionFactory) {
    return IntegrationFlows.from(...)
            ...
            .channel(Amqp.channel(connectionFactory)
                    .queueName("bar"))
            ...
            .get();
}

@Bean
public IntegrationFlow pubSubInFlow(ConnectionFactory connectionFactory) {
    return IntegrationFlows.from(...)
            ...
            .channel(Amqp.publisSubscribeChannel(connectionFactory)
                    .queueName("baz"))
            ...
            .get();
}

11.8 AMQP Message Headers

The Spring Integration AMQP Adapters will map standard AMQP properties automatically. These properties will be copied by default to and from Spring Integration MessageHeaders using the DefaultAmqpHeaderMapper.

Of course, you can pass in your own implementation of AMQP specific header mappers, as the adapters have respective properties to support that.

Any user-defined headers within the AMQP MessageProperties will NOT be copied to or from an AMQP Message, unless explicitly specified by the requestHeaderNames and/or replyHeaderNames properties of the DefaultAmqpHeaderMapper.

	Tip
	When mapping user-defined headers, the values can also contain simple wildcard patterns (e.g. "foo" or "foo") to be matched. For example, if you need to copy all user-defined headers simply use the wildcard character `*`, but see the CAUTION below.

Starting with version 4.1, the AbstractHeaderMapper (a DefaultAmqpHeaderMapper superclass) allows the NON_STANDARD_HEADERS token to be configured for the requestHeaderNames and/or replyHeaderNames properties (in addition to existing STANDARD_REQUEST_HEADERS and STANDARD_REPLY_HEADERS) to map all user-defined headers. Note, it is recommended to use the combination like this STANDARD_REPLY_HEADERS, NON_STANDARD_HEADERS instead of generic *, to avoid mapping of request headers to the reply.

Class org.springframework.amqp.support.AmqpHeaders identifies the default headers that will be used by the DefaultAmqpHeaderMapper:

amqp_appId
amqp_clusterId
amqp_contentEncoding
amqp_contentLength
content-type
amqp_correlationId
amqp_deliveryMode
amqp_deliveryTag
amqp_expiration
amqp_messageCount
amqp_messageId
amqp_receivedExchange
amqp_receivedRoutingKey
amqp_redelivered
amqp_replyTo
amqp_timestamp
amqp_type
amqp_userId
amqp_publishConfirm
amqp_publishConfirmNackCause
amqp_returnReplyCode
amqp_returnReplyText
amqp_returnExchange
amqp_returnRoutingKey

Caution

	Caution
As mentioned above, using a header mapping pattern `` is a common way to copy all headers. However, this can have some unexpected side-effects because certain RabbitMQ proprietary properties/headers will be copied as well. For example, when you use Federation, the received message may have a property named `x-received-from` which contains the node that sent the message. If you use the wildcard character `` for the request and reply header mapping on the Inbound Gateway, this header will be copied as well, which may cause some issues with federation; this reply message may be federated back to the sending broker, which will think that a message is looping and is thus silently dropped. If you wish to use the convenience of wildcard header mapping, you may need to filter out some headers in the downstream flow. For example, to avoid copying the `x-received-from` header back to the reply you can use `<int:header-filter ... header-names="x-received-from">` before sending the reply to the AMQP Inbound Gateway. Alternatively, you could explicitly list those properties that you actually want mapped instead of using wildcards.

As mentioned above, using a header mapping pattern * is a common way to copy all headers. However, this can have some unexpected side-effects because certain RabbitMQ proprietary properties/headers will be copied as well. For example, when you use Federation, the received message may have a property named x-received-from which contains the node that sent the message. If you use the wildcard character * for the request and reply header mapping on the Inbound Gateway, this header will be copied as well, which may cause some issues with federation; this reply message may be federated back to the sending broker, which will think that a message is looping and is thus silently dropped. If you wish to use the convenience of wildcard header mapping, you may need to filter out some headers in the downstream flow. For example, to avoid copying the x-received-from header back to the reply you can use <int:header-filter ... header-names="x-received-from"> before sending the reply to the AMQP Inbound Gateway. Alternatively, you could explicitly list those properties that you actually want mapped instead of using wildcards.

11.9 AMQP Samples

To experiment with the AMQP adapters, check out the samples available in the Spring Integration Samples Git repository at:

https://github.com/SpringSource/spring-integration-samples

Currently there is one sample available that demonstrates the basic functionality of the Spring Integration AMQP Adapter using an Outbound Channel Adapter and an Inbound Channel Adapter. As AMQP Broker implementation the sample uses RabbitMQ (http://www.rabbitmq.com/).

	Note
	In order to run the example you will need a running instance of RabbitMQ. A local installation with just the basic defaults will be sufficient. For detailed RabbitMQ installation procedures please visit: http://www.rabbitmq.com/install.html

Once the sample application is started, you enter some text on the command prompt and a message containing that entered text is dispatched to the AMQP queue. In return that message is retrieved via Spring Integration and then printed to the console.

The image belows illustrates the basic set of Spring Integration components used in this sample.

Figure 11.1. The Spring Integration graph of the AMQP sample

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