3.1.0-SNAPSHOT

Reference Guide

This guide describes the RabbitMQ implementation of the Spring Cloud Stream Binder. It contains information about its design, usage and configuration options, as well as information on how the Stream Cloud Stream concepts map into RabbitMQ specific constructs.

1. Usage

To use the RabbitMQ binder, you can add it to your Spring Cloud Stream application, by using the following Maven coordinates:

<dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-stream-binder-rabbit</artifactId>
</dependency>

Alternatively, you can use the Spring Cloud Stream RabbitMQ Starter, as follows:

<dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-starter-stream-rabbit</artifactId>
</dependency>

2. RabbitMQ Binder Overview

The following simplified diagram shows how the RabbitMQ binder operates:

Figure 1. RabbitMQ Binder

By default, the RabbitMQ Binder implementation maps each destination to a TopicExchange. For each consumer group, a Queue is bound to that TopicExchange. Each consumer instance has a corresponding RabbitMQ Consumer instance for its group’s Queue. For partitioned producers and consumers, the queues are suffixed with the partition index and use the partition index as the routing key. For anonymous consumers (those with no group property), an auto-delete queue (with a randomized unique name) is used.

By using the optional autoBindDlq option, you can configure the binder to create and configure dead-letter queues (DLQs) (and a dead-letter exchange DLX, as well as routing infrastructure). By default, the dead letter queue has the name of the destination, appended with .dlq. If retry is enabled (maxAttempts > 1), failed messages are delivered to the DLQ after retries are exhausted. If retry is disabled (maxAttempts = 1), you should set requeueRejected to false (the default) so that failed messages are routed to the DLQ, instead of being re-queued. In addition, republishToDlq causes the binder to publish a failed message to the DLQ (instead of rejecting it). This feature lets additional information (such as the stack trace in the x-exception-stacktrace header) be added to the message in headers. See the frameMaxHeadroom property for information about truncated stack traces. This option does not need retry enabled. You can republish a failed message after just one attempt. Starting with version 1.2, you can configure the delivery mode of republished messages. See the republishDeliveryMode property.

If the stream listener throws an ImmediateAcknowledgeAmqpException, the DLQ is bypassed and the message simply discarded. Starting with version 2.1, this is true regardless of the setting of republishToDlq; previously it was only the case when republishToDlq was false.

Setting requeueRejected to true (with republishToDlq=false ) causes the message to be re-queued and redelivered continually, which is likely not what you want unless the reason for the failure is transient. In general, you should enable retry within the binder by setting maxAttempts to greater than one or by setting republishToDlq to true.

See RabbitMQ Binder Properties for more information about these properties.

The framework does not provide any standard mechanism to consume dead-letter messages (or to re-route them back to the primary queue). Some options are described in Dead-Letter Queue Processing.

When multiple RabbitMQ binders are used in a Spring Cloud Stream application, it is important to disable 'RabbitAutoConfiguration' to avoid the same configuration from RabbitAutoConfiguration being applied to the two binders. You can exclude the class by using the @SpringBootApplication annotation.

Starting with version 2.0, the RabbitMessageChannelBinder sets the RabbitTemplate.userPublisherConnection property to true so that the non-transactional producers avoid deadlocks on consumers, which can happen if cached connections are blocked because of a memory alarm on the broker.

Currently, a multiplex consumer (a single consumer listening to multiple queues) is only supported for message-driven conssumers; polled consumers can only retrieve messages from a single queue.

3. Configuration Options

This section contains settings specific to the RabbitMQ Binder and bound channels.

For general binding configuration options and properties, see the Spring Cloud Stream core documentation.

3.1. RabbitMQ Binder Properties

By default, the RabbitMQ binder uses Spring Boot’s ConnectionFactory. Conseuqently, it supports all Spring Boot configuration options for RabbitMQ. (For reference, see the Spring Boot documentation). RabbitMQ configuration options use the spring.rabbitmq prefix.

In addition to Spring Boot options, the RabbitMQ binder supports the following properties:

spring.cloud.stream.rabbit.binder.adminAddresses: A comma-separated list of RabbitMQ management plugin URLs. Only used when nodes contains more than one entry. Each entry in this list must have a corresponding entry in spring.rabbitmq.addresses. Only needed if you use a RabbitMQ cluster and wish to consume from the node that hosts the queue. See Queue Affinity and the LocalizedQueueConnectionFactory for more information.

Default: empty.
spring.cloud.stream.rabbit.binder.nodes: A comma-separated list of RabbitMQ node names. When more than one entry, used to locate the server address where a queue is located. Each entry in this list must have a corresponding entry in spring.rabbitmq.addresses. Only needed if you use a RabbitMQ cluster and wish to consume from the node that hosts the queue. See Queue Affinity and the LocalizedQueueConnectionFactory for more information.

Default: empty.
spring.cloud.stream.rabbit.binder.compressionLevel: The compression level for compressed bindings. See java.util.zip.Deflater.

Default: 1 (BEST_LEVEL).
spring.cloud.stream.binder.connection-name-prefix: A connection name prefix used to name the connection(s) created by this binder. The name is this prefix followed by #n, where n increments each time a new connection is opened.

Default: none (Spring AMQP default).

3.2. RabbitMQ Consumer Properties

The following properties are available for Rabbit consumers only and must be prefixed with spring.cloud.stream.rabbit.bindings.<channelName>.consumer..

However if the same set of properties needs to be applied to most bindings, to avoid repetition, Spring Cloud Stream supports setting values for all channels, in the format of spring.cloud.stream.rabbit.default.<property>=<value>.

Also, keep in mind that binding specific property will override its equivalent in the default.

acknowledgeMode: The acknowledge mode.

Default: AUTO.
anonymousGroupPrefix: When the binding has no group property, an anonymous, auto-delete queue is bound to the destination exchange. The default naming stragegy for such queues results in a queue named anonymous.<base64 representation of a UUID>. Set this property to change the prefix to something other than the default.

Default: anonymous..
autoBindDlq: Whether to automatically declare the DLQ and bind it to the binder DLX.

Default: false.
bindingRoutingKey: The routing key with which to bind the queue to the exchange (if bindQueue is true). Can be multiple keys - see bindingRoutingKeyDelimiter. For partitioned destinations, -<instanceIndex> is appended to each key.

Default: #.
bindingRoutingKeyDelimiter: When this is not null, 'bindingRoutingKey' is considered to be a list of keys delimited by this value; often a comma is used.

Default: null.
bindQueue: Whether to declare the queue and bind it to the destination exchange. Set it to false if you have set up your own infrastructure and have previously created and bound the queue.

Default: true.
consumerTagPrefix: Used to create the consumer tag(s); will be appended by #n where n increments for each consumer created. Example: ${spring.application.name}-${spring.cloud.stream.bindings.input.group}-${spring.cloud.stream.instance-index}.

Default: none - the broker will generate random consumer tags.
containerType: Select the type of listener container to be used. See Choosing a Container in the Spring AMQP documentation for more information.

Default: simple
deadLetterQueueName: The name of the DLQ

Default: prefix+destination.dlq
deadLetterExchange: A DLX to assign to the queue. Relevant only if autoBindDlq is true.

Default: 'prefix+DLX'
deadLetterExchangeType: The type of the DLX to assign to the queue. Relevant only if autoBindDlq is true.

Default: 'direct'
deadLetterRoutingKey: A dead letter routing key to assign to the queue. Relevant only if autoBindDlq is true.

Default: destination
declareDlx: Whether to declare the dead letter exchange for the destination. Relevant only if autoBindDlq is true. Set to false if you have a pre-configured DLX.

Default: true.
declareExchange: Whether to declare the exchange for the destination.

Default: true.
delayedExchange: Whether to declare the exchange as a Delayed Message Exchange. Requires the delayed message exchange plugin on the broker. The x-delayed-type argument is set to the exchangeType.

Default: false.
dlqBindingArguments: Arguments applied when binding the dlq to the dead letter exchange; used with headers deadLetterExchangeType to specify headers to match on. For example …dlqBindingArguments.x-match=any, …dlqBindingArguments.someHeader=someValue.

Default: empty
dlqDeadLetterExchange: If a DLQ is declared, a DLX to assign to that queue.

Default: none
dlqDeadLetterRoutingKey: If a DLQ is declared, a dead letter routing key to assign to that queue.

Default: none
dlqExpires: How long before an unused dead letter queue is deleted (in milliseconds).

Default: no expiration
dlqLazy: Declare the dead letter queue with the x-queue-mode=lazy argument. See “Lazy Queues”. Consider using a policy instead of this setting, because using a policy allows changing the setting without deleting the queue.

Default: false.
dlqMaxLength: Maximum number of messages in the dead letter queue.

Default: no limit
dlqMaxLengthBytes: Maximum number of total bytes in the dead letter queue from all messages.

Default: no limit
dlqMaxPriority: Maximum priority of messages in the dead letter queue (0-255).

Default: none
dlqOverflowBehavior: Action to take when dlqMaxLength or dlqMaxLengthBytes is exceeded; currently drop-head or reject-publish but refer to the RabbitMQ documentation.

Default: none
dlqQuorum.deliveryLimit: When quorum.enabled=true, set a delivery limit after which the message is dropped or dead-lettered.

Default: none - broker default will apply.
dlqQuorum.enabled: When true, create a quorum dead letter queue instead of a classic queue.

Default: false
dlqQuorum.initialQuorumSize: When quorum.enabled=true, set the initial quorum size.

Default: none - broker default will apply.
dlqSingleActiveConsumer: Set to true to set the x-single-active-consumer queue property to true.

Default: false
dlqTtl: Default time to live to apply to the dead letter queue when declared (in milliseconds).

Default: no limit
durableSubscription: Whether the subscription should be durable. Only effective if group is also set.

Default: true.
exchangeAutoDelete: If declareExchange is true, whether the exchange should be auto-deleted (that is, removed after the last queue is removed).

Default: true.
exchangeDurable: If declareExchange is true, whether the exchange should be durable (that is, it survives broker restart).

Default: true.
exchangeType: The exchange type: direct, fanout, headers or topic for non-partitioned destinations and direct, headers or topic for partitioned destinations.

Default: topic.
exclusive: Whether to create an exclusive consumer. Concurrency should be 1 when this is true. Often used when strict ordering is required but enabling a hot standby instance to take over after a failure. See recoveryInterval, which controls how often a standby instance attempts to consume. Consider using singleActiveConsumer instead when using RabbitMQ 3.8 or later.

Default: false.
expires: How long before an unused queue is deleted (in milliseconds).

Default: no expiration
failedDeclarationRetryInterval: The interval (in milliseconds) between attempts to consume from a queue if it is missing.

Default: 5000

frameMaxHeadroom: The number of bytes to reserve for other headers when adding the stack trace to a DLQ message header. All headers must fit within the frame_max size configured on the broker. Stack traces can be large; if the size plus this property exceeds frame_max then the stack trace will be truncated. A WARN log will be written; consider increasing the frame_max or reducing the stack trace by catching the exception and throwing one with a smaller stack trace.

Default: 20000
headerPatterns: Patterns for headers to be mapped from inbound messages.

Default: ['*'] (all headers).
lazy: Declare the queue with the x-queue-mode=lazy argument. See “Lazy Queues”. Consider using a policy instead of this setting, because using a policy allows changing the setting without deleting the queue.

Default: false.
maxConcurrency: The maximum number of consumers. Not supported when the containerType is direct.

Default: 1.
maxLength: The maximum number of messages in the queue.

Default: no limit
maxLengthBytes: The maximum number of total bytes in the queue from all messages.

Default: no limit
maxPriority: The maximum priority of messages in the queue (0-255).

Default: none
missingQueuesFatal: When the queue cannot be found, whether to treat the condition as fatal and stop the listener container. Defaults to false so that the container keeps trying to consume from the queue — for example, when using a cluster and the node hosting a non-HA queue is down.

Default: false
overflowBehavior: Action to take when maxLength or maxLengthBytes is exceeded; currently drop-head or reject-publish but refer to the RabbitMQ documentation.

Default: none
prefetch: Prefetch count.

Default: 1.
prefix: A prefix to be added to the name of the destination and queues.

Default: "".
queueBindingArguments: Arguments applied when binding the queue to the exchange; used with headers exchangeType to specify headers to match on. For example …queueBindingArguments.x-match=any, …queueBindingArguments.someHeader=someValue.

Default: empty
queueDeclarationRetries: The number of times to retry consuming from a queue if it is missing. Relevant only when missingQueuesFatal is true. Otherwise, the container keeps retrying indefinitely. Not supported when the containerType is direct.

Default: 3
queueNameGroupOnly: When true, consume from a queue with a name equal to the group. Otherwise the queue name is destination.group. This is useful, for example, when using Spring Cloud Stream to consume from an existing RabbitMQ queue.

Default: false.
quorum.deliveryLimit: When quorum.enabled=true, set a delivery limit after which the message is dropped or dead-lettered.

Default: none - broker default will apply.
quorum.enabled: When true, create a quorum queue instead of a classic queue.

Default: false
quorum.initialQuorumSize: When quorum.enabled=true, set the initial quorum size.

Default: none - broker default will apply.
recoveryInterval: The interval between connection recovery attempts, in milliseconds.

Default: 5000.
requeueRejected: Whether delivery failures should be re-queued when retry is disabled or republishToDlq is false.

Default: false.

republishDeliveryMode: When republishToDlq is true, specifies the delivery mode of the republished message.

Default: DeliveryMode.PERSISTENT
republishToDlq: By default, messages that fail after retries are exhausted are rejected. If a dead-letter queue (DLQ) is configured, RabbitMQ routes the failed message (unchanged) to the DLQ. If set to true, the binder republishs failed messages to the DLQ with additional headers, including the exception message and stack trace from the cause of the final failure. Also see the frameMaxHeadroom property.

Default: true
singleActiveConsumer: Set to true to set the x-single-active-consumer queue property to true.

Default: false
transacted: Whether to use transacted channels.

Default: false.
ttl: Default time to live to apply to the queue when declared (in milliseconds).

Default: no limit
txSize: The number of deliveries between acks. Not supported when the containerType is direct.

Default: 1.

3.3. Advanced Listener Container Configuration

To set listener container properties that are not exposed as binder or binding properties, add a single bean of type ListenerContainerCustomizer to the application context. The binder and binding properties will be set and then the customizer will be called. The customizer (configure() method) is provided with the queue name as well as the consumer group as arguments.

3.4. Advanced Queue/Exchange/Binding Configuration

From time to time, the RabbitMQ team add new features that are enabled by setting some argument when declaring, for example, a queue. Generally, such features are enabled in the binder by adding appropriate properties, but this may not be immediately available in a current version. Starting with version 3.0.1, you can now add DeclarableCustomizer bean(s) to the application context to modify a Declarable (Queue, Exchange or Binding) just before the declaration is performed. This allows you to add arguments that are not currently directly supported by the binder.

3.5. Receiving Batched Messages

With the RabbitMQ binder, there are two types of batches handled by consumer bindings:

3.5.1. Batches Created by Producers

Normally, if a producer binding has batch-enabled=true (see Rabbit Producer Properties), or a message is created by a BatchingRabbitTemplate, elements of the batch are returned as individual calls to the listener method. Starting with version 3.0, any such batch can be presented as a List<?> to the listener method if spring.cloud.stream.bindings.<name>.consumer.batch-mode is set to true.

3.5.2. Consumer-side Batching

Starting with version 3.1, the consumer can be configured to assemble multiple inbound messages into a batch which is presented to the application as a List<?> of converted payloads. The following simple application demonstrates how to use this technique:

spring.cloud.stream.bindings.input-in-0.group=someGroup

spring.cloud.stream.bindings.input-in-0.consumer.batch-mode=true

spring.cloud.stream.rabbit.bindings.input-in-0.consumer.enable-batching=true
spring.cloud.stream.rabbit.bindings.input-in-0.consumer.batch-size=10
spring.cloud.stream.rabbit.bindings.input-in-0.consumer.receive-timeout=200

@SpringBootApplication
public class Application {

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}

	@Bean
	Consumer<List<Thing>> input() {
		return list -> {
			System.out.println("Received " + list.size());
			list.forEach(thing -> {
				System.out.println(thing);

				// ...

			});
		};
	}

	@Bean
	public ApplicationRunner runner(RabbitTemplate template) {
		return args -> {
			template.convertAndSend("input-in-0.someGroup", "{\"field\":\"value1\"}");
			template.convertAndSend("input-in-0.someGroup", "{\"field\":\"value2\"}");
		};
	}

	public static class Thing {

		private String field;

		public Thing() {
		}

		public Thing(String field) {
			this.field = field;
		}

		public String getField() {
			return this.field;
		}

		public void setField(String field) {
			this.field = field;
		}

		@Override
		public String toString() {
			return "Thing [field=" + this.field + "]";
		}

	}

}

Received 2
Thing [field=value1]
Thing [field=value2]

The number of messages in a batch is specified by the batch-size and receive-timeout properties; if the receive-timeout elapses with no new messages, a "short" batch is delivered.

Consumer-side batching is only supported with container-type=simple (the default).

If you wish to examine headers of consumer-side batched messages, you should consume Message<List<?>>; the headers are a List<Map<String, Object>> in a header AmqpInboundChannelAdapter.CONSOLIDATED_HEADERS, with the headers for each payload element in the corresponding index. Again, here is a simple example:

@SpringBootApplication
public class Application {

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}

	@Bean
	Consumer<Message<List<Thing>>> input() {
		return msg -> {
			List<Thing> things = msg.getPayload();
			System.out.println("Received " + things.size());
			@SuppressWarnings("unchecked")
			List<Map<String, Object>> headers =
					(List<Map<String, Object>>) msg.getHeaders().get(AmqpInboundChannelAdapter.CONSOLIDATED_HEADERS);
			for (int i = 0; i < things.size(); i++) {
				System.out.println(things.get(i) + " myHeader=" + headers.get(i).get("myHeader"));

				// ...

			}
		};
	}

	@Bean
	public ApplicationRunner runner(RabbitTemplate template) {
		return args -> {
			template.convertAndSend("input-in-0.someGroup", "{\"field\":\"value1\"}", msg -> {
				msg.getMessageProperties().setHeader("myHeader", "headerValue1");
				return msg;
			});
			template.convertAndSend("input-in-0.someGroup", "{\"field\":\"value2\"}", msg -> {
				msg.getMessageProperties().setHeader("myHeader", "headerValue2");
				return msg;
			});
		};
	}

	public static class Thing {

		private String field;

		public Thing() {
		}

		public Thing(String field) {
			this.field = field;
		}

		public String getfield() {
			return this.field;
		}

		public void setfield(String field) {
			this.field = field;
		}

		@Override
		public String toString() {
			return "Thing [field=" + this.field + "]";
		}

	}

}

Received 2
Thing [field=value1] myHeader=headerValue1
Thing [field=value2] myHeader=headerValue2

3.6. Rabbit Producer Properties

The following properties are available for Rabbit producers only and must be prefixed with spring.cloud.stream.rabbit.bindings.<channelName>.producer..

Also, keep in mind that binding specific property will override its equivalent in the default.

autoBindDlq

Whether to automatically declare the DLQ and bind it to the binder DLX.

Default: false.

batchingEnabled

Whether to enable message batching by producers. Messages are batched into one message according to the following properties (described in the next three entries in this list): 'batchSize', batchBufferLimit, and batchTimeout. See Batching for more information. Also see Receiving Batched Messages.

Default: false.

batchSize

The number of messages to buffer when batching is enabled.

Default: 100.

batchBufferLimit

The maximum buffer size when batching is enabled.

Default: 10000.

batchTimeout

The batch timeout when batching is enabled.

Default: 5000.

bindingRoutingKey

The routing key with which to bind the queue to the exchange (if bindQueue is true). Can be multiple keys - see bindingRoutingKeyDelimiter. For partitioned destinations, -n is appended to each key. Only applies if requiredGroups are provided and then only to those groups.

Default: #.

bindingRoutingKeyDelimiter

When this is not null, 'bindingRoutingKey' is considered to be a list of keys delimited by this value; often a comma is used. Only applies if requiredGroups are provided and then only to those groups.

Default: null.

bindQueue

Whether to declare the queue and bind it to the destination exchange. Set it to false if you have set up your own infrastructure and have previously created and bound the queue. Only applies if requiredGroups are provided and then only to those groups.

Default: true.

compress

Whether data should be compressed when sent.

Default: false.

confirmAckChannel

When errorChannelEnabled is true, a channel to which to send positive delivery acknowledgments (aka publisher confirms). If the channel does not exist, a DirectChannel is registered with this name. The connection factory must be configured to enable publisher confirms. Mutually exclusive with useConfirmHeader.

Default: nullChannel (acks are discarded).

deadLetterQueueName

The name of the DLQ Only applies if requiredGroups are provided and then only to those groups.

Default: prefix+destination.dlq

deadLetterExchange

A DLX to assign to the queue. Relevant only when autoBindDlq is true. Applies only when requiredGroups are provided and then only to those groups.

Default: 'prefix+DLX'

deadLetterExchangeType

The type of the DLX to assign to the queue. Relevant only if autoBindDlq is true. Applies only when requiredGroups are provided and then only to those groups.

Default: 'direct'

deadLetterRoutingKey

A dead letter routing key to assign to the queue. Relevant only when autoBindDlq is true. Applies only when requiredGroups are provided and then only to those groups.

Default: destination

declareDlx

Whether to declare the dead letter exchange for the destination. Relevant only if autoBindDlq is true. Set to false if you have a pre-configured DLX. Applies only when requiredGroups are provided and then only to those groups.

Default: true.

declareExchange

Whether to declare the exchange for the destination.

Default: true.

delayExpression

A SpEL expression to evaluate the delay to apply to the message (x-delay header). It has no effect if the exchange is not a delayed message exchange.

Default: No x-delay header is set.

delayedExchange

Whether to declare the exchange as a Delayed Message Exchange. Requires the delayed message exchange plugin on the broker. The x-delayed-type argument is set to the exchangeType.

Default: false.

deliveryMode

The delivery mode.

Default: PERSISTENT.

dlqBindingArguments

Arguments applied when binding the dlq to the dead letter exchange; used with headers deadLetterExchangeType to specify headers to match on. For example …dlqBindingArguments.x-match=any, …dlqBindingArguments.someHeader=someValue. Applies only when requiredGroups are provided and then only to those groups.

Default: empty

dlqDeadLetterExchange

When a DLQ is declared, a DLX to assign to that queue. Applies only if requiredGroups are provided and then only to those groups.

Default: none

dlqDeadLetterRoutingKey

When a DLQ is declared, a dead letter routing key to assign to that queue. Applies only when requiredGroups are provided and then only to those groups.

Default: none

dlqExpires

How long (in milliseconds) before an unused dead letter queue is deleted. Applies only when requiredGroups are provided and then only to those groups.

Default: no expiration

dlqLazy

Declare the dead letter queue with the x-queue-mode=lazy argument. See “Lazy Queues”. Consider using a policy instead of this setting, because using a policy allows changing the setting without deleting the queue. Applies only when requiredGroups are provided and then only to those groups.

dlqMaxLength

Maximum number of messages in the dead letter queue. Applies only if requiredGroups are provided and then only to those groups.

Default: no limit

dlqMaxLengthBytes

Maximum number of total bytes in the dead letter queue from all messages. Applies only when requiredGroups are provided and then only to those groups.

Default: no limit

dlqMaxPriority

Maximum priority of messages in the dead letter queue (0-255) Applies only when requiredGroups are provided and then only to those groups.

Default: none

dlqQuorum.deliveryLimit

When quorum.enabled=true, set a delivery limit after which the message is dropped or dead-lettered. Applies only when requiredGroups are provided and then only to those groups.

Default: none - broker default will apply.

dlqQuorum.enabled

When true, create a quorum dead letter queue instead of a classic queue. Applies only when requiredGroups are provided and then only to those groups.

Default: false

dlqQuorum.initialQuorumSize

When quorum.enabled=true, set the initial quorum size. Applies only when requiredGroups are provided and then only to those groups.

Default: none - broker default will apply.

dlqSingleActiveConsumer

Set to true to set the x-single-active-consumer queue property to true. Applies only when requiredGroups are provided and then only to those groups.

Default: false

dlqTtl

Default time (in milliseconds) to live to apply to the dead letter queue when declared. Applies only when requiredGroups are provided and then only to those groups.

Default: no limit

exchangeAutoDelete

If declareExchange is true, whether the exchange should be auto-delete (it is removed after the last queue is removed).

Default: true.

exchangeDurable

If declareExchange is true, whether the exchange should be durable (survives broker restart).

Default: true.

exchangeType

The exchange type: direct, fanout, headers or topic for non-partitioned destinations and direct, headers or topic for partitioned destinations.

Default: topic.

expires

How long (in milliseconds) before an unused queue is deleted. Applies only when requiredGroups are provided and then only to those groups.

Default: no expiration

headerPatterns

Patterns for headers to be mapped to outbound messages.

Default: ['*'] (all headers).

lazy

Declare the queue with the x-queue-mode=lazy argument. See “Lazy Queues”. Consider using a policy instead of this setting, because using a policy allows changing the setting without deleting the queue. Applies only when requiredGroups are provided and then only to those groups.

Default: false.

maxLength

Maximum number of messages in the queue. Applies only when requiredGroups are provided and then only to those groups.

Default: no limit

maxLengthBytes

Maximum number of total bytes in the queue from all messages. Only applies if requiredGroups are provided and then only to those groups.

Default: no limit

maxPriority

Maximum priority of messages in the queue (0-255). Only applies if requiredGroups are provided and then only to those groups.

Default: none

prefix

A prefix to be added to the name of the destination exchange.

Default: "".

queueBindingArguments

Arguments applied when binding the queue to the exchange; used with headers exchangeType to specify headers to match on. For example …queueBindingArguments.x-match=any, …queueBindingArguments.someHeader=someValue. Applies only when requiredGroups are provided and then only to those groups.

Default: empty

queueNameGroupOnly

When true, consume from a queue with a name equal to the group. Otherwise the queue name is destination.group. This is useful, for example, when using Spring Cloud Stream to consume from an existing RabbitMQ queue. Applies only when requiredGroups are provided and then only to those groups.

Default: false.

quorum.deliveryLimit

When quorum.enabled=true, set a delivery limit after which the message is dropped or dead-lettered. Applies only when requiredGroups are provided and then only to those groups.

Default: none - broker default will apply.

quorum.enabled

When true, create a quorum queue instead of a classic queue. Applies only when requiredGroups are provided and then only to those groups.

Default: false

quorum.initialQuorumSize

When quorum.enabled=true, set the initial quorum size. Applies only when requiredGroups are provided and then only to those groups.

Default: none - broker default will apply.

routingKeyExpression

A SpEL expression to determine the routing key to use when publishing messages. For a fixed routing key, use a literal expression, such as routingKeyExpression='my.routingKey' in a properties file or routingKeyExpression: '''my.routingKey''' in a YAML file.

Default: destination or destination-<partition> for partitioned destinations.

singleActiveConsumer

Set to true to set the x-single-active-consumer queue property to true. Applies only when requiredGroups are provided and then only to those groups.

Default: false

transacted

Whether to use transacted channels.

Default: false.

ttl

Default time (in milliseconds) to live to apply to the queue when declared. Applies only when requiredGroups are provided and then only to those groups.

Default: no limit

useConfirmHeader

See Publisher Confirms. Mutually exclusive with confirmAckChannel.

In the case of RabbitMQ, content type headers can be set by external applications. Spring Cloud Stream supports them as part of an extended internal protocol used for any type of transport — including transports, such as Kafka (prior to 0.11), that do not natively support headers.

3.7. Publisher Confirms

There are two mechanisms to get the result of publishing a message; in each case, the connection factory must have publisherConfirmType set ConfirmType.CORRELATED. The "legacy" mechanism is to set the confirmAckChannel to the bean name of a message channel from which you can retrieve the confirmations asynchronously; negative acks are sent to the error channel (if enabled) - see Error Channels.

The preferred mechanism, added in version 3.1 is to use a correlation data header and wait for the result via its Future<Confirm> property. This is particularly useful with a batch listener because you can send multiple messages before waiting for the result. To use this technique, set the useConfirmHeader property to true The following simple application is an example of using this technique:

spring.cloud.stream.bindings.input-in-0.group=someGroup
spring.cloud.stream.bindings.input-in-0.consumer.batch-mode=true

spring.cloud.stream.source=output
spring.cloud.stream.bindings.output-out-0.producer.error-channel-enabled=true

spring.cloud.stream.rabbit.bindings.output-out-0.producer.useConfirmHeader=true
spring.cloud.stream.rabbit.bindings.input-in-0.consumer.auto-bind-dlq=true
spring.cloud.stream.rabbit.bindings.input-in-0.consumer.batch-size=10

spring.rabbitmq.publisher-confirm-type=correlated
spring.rabbitmq.publisher-returns=true

@SpringBootApplication
public class Application {

	private static final Logger log = LoggerFactory.getLogger(Application.class);

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}

	@Autowired
	private StreamBridge bridge;

	@Bean
	Consumer<List<String>> input() {
		return list -> {
			List<MyCorrelationData> results = new ArrayList<>();
			list.forEach(str -> {
				log.info("Received: " + str);
				MyCorrelationData corr = new MyCorrelationData(UUID.randomUUID().toString(), str);
				results.add(corr);
				this.bridge.send("output-out-0", MessageBuilder.withPayload(str.toUpperCase())
						.setHeader(AmqpHeaders.PUBLISH_CONFIRM_CORRELATION, corr)
						.build());
			});
			results.forEach(correlation -> {
				try {
					Confirm confirm = correlation.getFuture().get(10, TimeUnit.SECONDS);
					log.info(confirm + " for " + correlation.getPayload());
					if (correlation.getReturnedMessage() != null) {
						log.error("Message for " + correlation.getPayload() + " was returned ");

						// try to re-publish, send a DLQ, etc

					}
				}
				catch (InterruptedException e) {
					Thread.currentThread().interrupt();
					e.printStackTrace();
				}
				catch (ExecutionException | TimeoutException e) {
					e.printStackTrace();
				}
			});
		};
	}


	@Bean
	public ApplicationRunner runner(BatchingRabbitTemplate template) {
		return args -> IntStream.range(0, 10).forEach(i ->
				template.convertAndSend("input-in-0", "input-in-0.rbgh303", "foo" + i));
	}

	@Bean
	public BatchingRabbitTemplate template(CachingConnectionFactory cf, TaskScheduler taskScheduler) {
		BatchingStrategy batchingStrategy = new SimpleBatchingStrategy(10, 1000000, 1000);
		return new BatchingRabbitTemplate(cf, batchingStrategy, taskScheduler);
	}

}

class MyCorrelationData extends CorrelationData {

	private final String payload;

	MyCorrelationData(String id, String payload) {
		super(id);
		this.payload = payload;
	}

	public String getPayload() {
		return this.payload;
	}

}

As you can see, we send each message and then await for the publication results. If the messages can’t be routed, then correlation data is populated with the returned message before the future is completed.

The correlation data must be provided with a unique id so that the framework can perform the correlation.

You cannot set both useConfirmHeader and confirmAckChannel but you can still receive returned messages in the error channel when useConfirmHeader is true, but using the correlation header is more convenient.

4. Using Existing Queues/Exchanges

By default, the binder will automatically provision a topic exchange with the name being derived from the value of the destination binding property <prefix><destination>. The destination defaults to the binding name, if not provided. When binding a consumer, a queue will automatically be provisioned with the name <prefix><destination>.<group> (if a group binding property is specified), or an anonymous, auto-delete queue when there is no group. The queue will be bound to the exchange with the "match-all" wildcard routing key (#) for a non-partitioned binding or <destination>-<instanceIndex> for a partitioned binding. The prefix is an empty String by default. If an output binding is specified with requiredGroups, a queue/binding will be provisioned for each group.

There are a number of rabbit-specific binding properties that allow you to modify this default behavior.

If you have an existing exchange/queue that you wish to use, you can completely disable automatic provisioning as follows, assuming the exchange is named myExchange and the queue is named myQueue:

spring.cloud.stream.bindings.<binding name>.destination=myExhange
spring.cloud.stream.bindings.<binding name>.group=myQueue
spring.cloud.stream.rabbit.bindings.<binding name>.consumer.bindQueue=false
spring.cloud.stream.rabbit.bindings.<binding name>.consumer.declareExchange=false
spring.cloud.stream.rabbit.bindings.<binding name>.consumer.queueNameGroupOnly=true

If you want the binder to provision the queue/exchange, but you want to do it using something other than the defaults discussed here, use the following properties. Refer to the property documentation above for more information.

spring.cloud.stream.rabbit.bindings.<binding name>.consumer.bindingRoutingKey=myRoutingKey
spring.cloud.stream.rabbit.bindings.<binding name>.consumer.exchangeType=<type>
spring.cloud.stream.rabbit.bindings.<binding name>.producer.routingKeyExpression='myRoutingKey'

There are similar properties used when declaring a dead-letter exchange/queue, when autoBindDlq is true.

5. Retry With the RabbitMQ Binder

When retry is enabled within the binder, the listener container thread is suspended for any back off periods that are configured. This might be important when strict ordering is required with a single consumer. However, for other use cases, it prevents other messages from being processed on that thread. An alternative to using binder retry is to set up dead lettering with time to live on the dead-letter queue (DLQ) as well as dead-letter configuration on the DLQ itself. See “RabbitMQ Binder Properties” for more information about the properties discussed here. You can use the following example configuration to enable this feature:

Set autoBindDlq to true. The binder create a DLQ. Optionally, you can specify a name in deadLetterQueueName.
Set dlqTtl to the back off time you want to wait between redeliveries.
Set the dlqDeadLetterExchange to the default exchange. Expired messages from the DLQ are routed to the original queue, because the default deadLetterRoutingKey is the queue name (destination.group). Setting to the default exchange is achieved by setting the property with no value, as shown in the next example.

To force a message to be dead-lettered, either throw an AmqpRejectAndDontRequeueException or set requeueRejected to false (the default) and throw any exception.

The loop continue without end, which is fine for transient problems, but you may want to give up after some number of attempts. Fortunately, RabbitMQ provides the x-death header, which lets you determine how many cycles have occurred.

To acknowledge a message after giving up, throw an ImmediateAcknowledgeAmqpException.

5.1. Putting it All Together

The following configuration creates an exchange myDestination with queue myDestination.consumerGroup bound to a topic exchange with a wildcard routing key #:

---
spring.cloud.stream.bindings.input.destination=myDestination
spring.cloud.stream.bindings.input.group=consumerGroup
#disable binder retries
spring.cloud.stream.bindings.input.consumer.max-attempts=1
#dlx/dlq setup
spring.cloud.stream.rabbit.bindings.input.consumer.auto-bind-dlq=true
spring.cloud.stream.rabbit.bindings.input.consumer.dlq-ttl=5000
spring.cloud.stream.rabbit.bindings.input.consumer.dlq-dead-letter-exchange=
---

This configuration creates a DLQ bound to a direct exchange (DLX) with a routing key of myDestination.consumerGroup. When messages are rejected, they are routed to the DLQ. After 5 seconds, the message expires and is routed to the original queue by using the queue name as the routing key, as shown in the following example:

Spring Boot application

@SpringBootApplication
@EnableBinding(Sink.class)
public class XDeathApplication {

    public static void main(String[] args) {
        SpringApplication.run(XDeathApplication.class, args);
    }

    @StreamListener(Sink.INPUT)
    public void listen(String in, @Header(name = "x-death", required = false) Map<?,?> death) {
        if (death != null && death.get("count").equals(3L)) {
            // giving up - don't send to DLX
            throw new ImmediateAcknowledgeAmqpException("Failed after 4 attempts");
        }
        throw new AmqpRejectAndDontRequeueException("failed");
    }

}

Notice that the count property in the x-death header is a Long.

6. Error Channels

Starting with version 1.3, the binder unconditionally sends exceptions to an error channel for each consumer destination and can also be configured to send async producer send failures to an error channel. See “[spring-cloud-stream-overview-error-handling]” for more information.

RabbitMQ has two types of send failures:

Returned messages,
Negatively acknowledged Publisher Confirms.

The latter is rare. According to the RabbitMQ documentation "[A nack] will only be delivered if an internal error occurs in the Erlang process responsible for a queue.". You can also get a negative acknowledgment if you publish to a bounded queue with reject-publish queue overflow behavior.

As well as enabling producer error channels (as described in “[spring-cloud-stream-overview-error-handling]”), the RabbitMQ binder only sends messages to the channels if the connection factory is appropriately configured, as follows:

ccf.setPublisherConfirms(true);
ccf.setPublisherReturns(true);

When using Spring Boot configuration for the connection factory, set the following properties:

spring.rabbitmq.publisher-confirms
spring.rabbitmq.publisher-returns

The payload of the ErrorMessage for a returned message is a ReturnedAmqpMessageException with the following properties:

failedMessage: The spring-messaging Message<?> that failed to be sent.
amqpMessage: The raw spring-amqp Message.
replyCode: An integer value indicating the reason for the failure (for example, 312 - No route).
replyText: A text value indicating the reason for the failure (for example, NO_ROUTE).
exchange: The exchange to which the message was published.
routingKey: The routing key used when the message was published.

Also see Publisher Confirms for an alternative mechanism to receive returned messages.

For negatively acknowledged confirmations, the payload is a NackedAmqpMessageException with the following properties:

failedMessage: The spring-messaging Message<?> that failed to be sent.
nackReason: A reason (if available — you may need to examine the broker logs for more information).

There is no automatic handling of these exceptions (such as sending to a dead-letter queue). You can consume these exceptions with your own Spring Integration flow.

7. Dead-Letter Queue Processing

Because you cannot anticipate how users would want to dispose of dead-lettered messages, the framework does not provide any standard mechanism to handle them. If the reason for the dead-lettering is transient, you may wish to route the messages back to the original queue. However, if the problem is a permanent issue, that could cause an infinite loop. The following Spring Boot application shows an example of how to route those messages back to the original queue but moves them to a third “parking lot” queue after three attempts. The second example uses the RabbitMQ Delayed Message Exchange to introduce a delay to the re-queued message. In this example, the delay increases for each attempt. These examples use a @RabbitListener to receive messages from the DLQ. You could also use RabbitTemplate.receive() in a batch process.

The examples assume the original destination is so8400in and the consumer group is so8400.

7.1. Non-Partitioned Destinations

The first two examples are for when the destination is not partitioned:

@SpringBootApplication
public class ReRouteDlqApplication {

    private static final String ORIGINAL_QUEUE = "so8400in.so8400";

    private static final String DLQ = ORIGINAL_QUEUE + ".dlq";

    private static final String PARKING_LOT = ORIGINAL_QUEUE + ".parkingLot";

    private static final String X_RETRIES_HEADER = "x-retries";

    public static void main(String[] args) throws Exception {
        ConfigurableApplicationContext context = SpringApplication.run(ReRouteDlqApplication.class, args);
        System.out.println("Press enter to exit");
        System.in.read();
        context.close();
    }

    @Autowired
    private RabbitTemplate rabbitTemplate;

    @RabbitListener(queues = DLQ)
    public void rePublish(Message failedMessage) {
        Integer retriesHeader = (Integer) failedMessage.getMessageProperties().getHeaders().get(X_RETRIES_HEADER);
        if (retriesHeader == null) {
            retriesHeader = Integer.valueOf(0);
        }
        if (retriesHeader < 3) {
            failedMessage.getMessageProperties().getHeaders().put(X_RETRIES_HEADER, retriesHeader + 1);
            this.rabbitTemplate.send(ORIGINAL_QUEUE, failedMessage);
        }
        else {
            this.rabbitTemplate.send(PARKING_LOT, failedMessage);
        }
    }

    @Bean
    public Queue parkingLot() {
        return new Queue(PARKING_LOT);
    }

}

@SpringBootApplication
public class ReRouteDlqApplication {

    private static final String ORIGINAL_QUEUE = "so8400in.so8400";

    private static final String DLQ = ORIGINAL_QUEUE + ".dlq";

    private static final String PARKING_LOT = ORIGINAL_QUEUE + ".parkingLot";

    private static final String X_RETRIES_HEADER = "x-retries";

    private static final String DELAY_EXCHANGE = "dlqReRouter";

    public static void main(String[] args) throws Exception {
        ConfigurableApplicationContext context = SpringApplication.run(ReRouteDlqApplication.class, args);
        System.out.println("Press enter to exit");
        System.in.read();
        context.close();
    }

    @Autowired
    private RabbitTemplate rabbitTemplate;

    @RabbitListener(queues = DLQ)
    public void rePublish(Message failedMessage) {
        Map<String, Object> headers = failedMessage.getMessageProperties().getHeaders();
        Integer retriesHeader = (Integer) headers.get(X_RETRIES_HEADER);
        if (retriesHeader == null) {
            retriesHeader = Integer.valueOf(0);
        }
        if (retriesHeader < 3) {
            headers.put(X_RETRIES_HEADER, retriesHeader + 1);
            headers.put("x-delay", 5000 * retriesHeader);
            this.rabbitTemplate.send(DELAY_EXCHANGE, ORIGINAL_QUEUE, failedMessage);
        }
        else {
            this.rabbitTemplate.send(PARKING_LOT, failedMessage);
        }
    }

    @Bean
    public DirectExchange delayExchange() {
        DirectExchange exchange = new DirectExchange(DELAY_EXCHANGE);
        exchange.setDelayed(true);
        return exchange;
    }

    @Bean
    public Binding bindOriginalToDelay() {
        return BindingBuilder.bind(new Queue(ORIGINAL_QUEUE)).to(delayExchange()).with(ORIGINAL_QUEUE);
    }

    @Bean
    public Queue parkingLot() {
        return new Queue(PARKING_LOT);
    }

}

7.2. Partitioned Destinations

With partitioned destinations, there is one DLQ for all partitions. We determine the original queue from the headers.

7.2.1. `republishToDlq=false`

When republishToDlq is false, RabbitMQ publishes the message to the DLX/DLQ with an x-death header containing information about the original destination, as shown in the following example:

@SpringBootApplication
public class ReRouteDlqApplication {

	private static final String ORIGINAL_QUEUE = "so8400in.so8400";

	private static final String DLQ = ORIGINAL_QUEUE + ".dlq";

	private static final String PARKING_LOT = ORIGINAL_QUEUE + ".parkingLot";

	private static final String X_DEATH_HEADER = "x-death";

	private static final String X_RETRIES_HEADER = "x-retries";

	public static void main(String[] args) throws Exception {
		ConfigurableApplicationContext context = SpringApplication.run(ReRouteDlqApplication.class, args);
		System.out.println("Press enter to exit");
		System.in.read();
		context.close();
	}

	@Autowired
	private RabbitTemplate rabbitTemplate;

	@SuppressWarnings("unchecked")
	@RabbitListener(queues = DLQ)
	public void rePublish(Message failedMessage) {
		Map<String, Object> headers = failedMessage.getMessageProperties().getHeaders();
		Integer retriesHeader = (Integer) headers.get(X_RETRIES_HEADER);
		if (retriesHeader == null) {
			retriesHeader = Integer.valueOf(0);
		}
		if (retriesHeader < 3) {
			headers.put(X_RETRIES_HEADER, retriesHeader + 1);
			List<Map<String, ?>> xDeath = (List<Map<String, ?>>) headers.get(X_DEATH_HEADER);
			String exchange = (String) xDeath.get(0).get("exchange");
			List<String> routingKeys = (List<String>) xDeath.get(0).get("routing-keys");
			this.rabbitTemplate.send(exchange, routingKeys.get(0), failedMessage);
		}
		else {
			this.rabbitTemplate.send(PARKING_LOT, failedMessage);
		}
	}

	@Bean
	public Queue parkingLot() {
		return new Queue(PARKING_LOT);
	}

}

7.2.2. `republishToDlq=true`

When republishToDlq is true, the republishing recoverer adds the original exchange and routing key to headers, as shown in the following example:

@SpringBootApplication
public class ReRouteDlqApplication {

	private static final String ORIGINAL_QUEUE = "so8400in.so8400";

	private static final String DLQ = ORIGINAL_QUEUE + ".dlq";

	private static final String PARKING_LOT = ORIGINAL_QUEUE + ".parkingLot";

	private static final String X_RETRIES_HEADER = "x-retries";

	private static final String X_ORIGINAL_EXCHANGE_HEADER = RepublishMessageRecoverer.X_ORIGINAL_EXCHANGE;

	private static final String X_ORIGINAL_ROUTING_KEY_HEADER = RepublishMessageRecoverer.X_ORIGINAL_ROUTING_KEY;

	public static void main(String[] args) throws Exception {
		ConfigurableApplicationContext context = SpringApplication.run(ReRouteDlqApplication.class, args);
		System.out.println("Press enter to exit");
		System.in.read();
		context.close();
	}

	@Autowired
	private RabbitTemplate rabbitTemplate;

	@RabbitListener(queues = DLQ)
	public void rePublish(Message failedMessage) {
		Map<String, Object> headers = failedMessage.getMessageProperties().getHeaders();
		Integer retriesHeader = (Integer) headers.get(X_RETRIES_HEADER);
		if (retriesHeader == null) {
			retriesHeader = Integer.valueOf(0);
		}
		if (retriesHeader < 3) {
			headers.put(X_RETRIES_HEADER, retriesHeader + 1);
			String exchange = (String) headers.get(X_ORIGINAL_EXCHANGE_HEADER);
			String originalRoutingKey = (String) headers.get(X_ORIGINAL_ROUTING_KEY_HEADER);
			this.rabbitTemplate.send(exchange, originalRoutingKey, failedMessage);
		}
		else {
			this.rabbitTemplate.send(PARKING_LOT, failedMessage);
		}
	}

	@Bean
	public Queue parkingLot() {
		return new Queue(PARKING_LOT);
	}

}

8. Partitioning with the RabbitMQ Binder

RabbitMQ does not support partitioning natively.

Sometimes, it is advantageous to send data to specific partitions — for example, when you want to strictly order message processing, all messages for a particular customer should go to the same partition.

The RabbitMessageChannelBinder provides partitioning by binding a queue for each partition to the destination exchange.

The following Java and YAML examples show how to configure the producer:

Producer

@SpringBootApplication
@EnableBinding(Source.class)
public class RabbitPartitionProducerApplication {

    private static final Random RANDOM = new Random(System.currentTimeMillis());

    private static final String[] data = new String[] {
            "abc1", "def1", "qux1",
            "abc2", "def2", "qux2",
            "abc3", "def3", "qux3",
            "abc4", "def4", "qux4",
            };

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

    @InboundChannelAdapter(channel = Source.OUTPUT, poller = @Poller(fixedRate = "5000"))
    public Message<?> generate() {
        String value = data[RANDOM.nextInt(data.length)];
        System.out.println("Sending: " + value);
        return MessageBuilder.withPayload(value)
                .setHeader("partitionKey", value)
                .build();
    }

}

application.yml

    spring:
      cloud:
        stream:
          bindings:
            output:
              destination: partitioned.destination
              producer:
                partitioned: true
                partition-key-expression: headers['partitionKey']
                partition-count: 2
                required-groups:
                - myGroup

The configuration in the prececing example uses the default partitioning (key.hashCode() % partitionCount). This may or may not provide a suitably balanced algorithm, depending on the key values. You can override this default by using the partitionSelectorExpression or partitionSelectorClass properties.

The required-groups property is required only if you need the consumer queues to be provisioned when the producer is deployed. Otherwise, any messages sent to a partition are lost until the corresponding consumer is deployed.

The following configuration provisions a topic exchange:

The following queues are bound to that exchange:

The following bindings associate the queues to the exchange:

The following Java and YAML examples continue the previous examples and show how to configure the consumer:

Consumer

@SpringBootApplication
@EnableBinding(Sink.class)
public class RabbitPartitionConsumerApplication {

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

    @StreamListener(Sink.INPUT)
    public void listen(@Payload String in, @Header(AmqpHeaders.CONSUMER_QUEUE) String queue) {
        System.out.println(in + " received from queue " + queue);
    }

}

application.yml

    spring:
      cloud:
        stream:
          bindings:
            input:
              destination: partitioned.destination
              group: myGroup
              consumer:
                partitioned: true
                instance-index: 0

The RabbitMessageChannelBinder does not support dynamic scaling. There must be at least one consumer per partition. The consumer’s instanceIndex is used to indicate which partition is consumed. Platforms such as Cloud Foundry can have only one instance with an instanceIndex.

Appendices

Appendix A: Building

A.1. Basic Compile and Test

To build the source you will need to install JDK 1.8.

The build uses the Maven wrapper so you don’t have to install a specific version of Maven. To enable the tests, you should have RabbitMQ server running on localhost and the default port (5672) before building.

The main build command is

$ ./mvnw clean install

You can also add '-DskipTests' if you like, to avoid running the tests.

You can also install Maven (>=3.3.3) yourself and run the mvn command in place of ./mvnw in the examples below. If you do that you also might need to add -P spring if your local Maven settings do not contain repository declarations for spring pre-release artifacts.

Be aware that you might need to increase the amount of memory available to Maven by setting a MAVEN_OPTS environment variable with a value like -Xmx512m -XX:MaxPermSize=128m. We try to cover this in the .mvn configuration, so if you find you have to do it to make a build succeed, please raise a ticket to get the settings added to source control.

The projects that require middleware generally include a docker-compose.yml, so consider using Docker Compose to run the middeware servers in Docker containers.

A.2. Documentation

There is a "docs" profile that will generate documentation.

./mvnw clean package -Pdocs -DskipTests

The reference documentation can then be found in docs/target/contents/reference.

A.3. Working with the code

If you don’t have an IDE preference we would recommend that you use Spring Tools Suite or Eclipse when working with the code. We use the m2eclipe eclipse plugin for maven support. Other IDEs and tools should also work without issue.

A.3.1. Importing into eclipse with m2eclipse

We recommend the m2eclipe eclipse plugin when working with eclipse. If you don’t already have m2eclipse installed it is available from the "eclipse marketplace".

Unfortunately m2e does not yet support Maven 3.3, so once the projects are imported into Eclipse you will also need to tell m2eclipse to use the .settings.xml file for the projects. If you do not do this you may see many different errors related to the POMs in the projects. Open your Eclipse preferences, expand the Maven preferences, and select User Settings. In the User Settings field click Browse and navigate to the Spring Cloud project you imported selecting the .settings.xml file in that project. Click Apply and then OK to save the preference changes.

Alternatively you can copy the repository settings from .settings.xml into your own ~/.m2/settings.xml.

A.3.2. Importing into eclipse without m2eclipse

If you prefer not to use m2eclipse you can generate eclipse project metadata using the following command:

$ ./mvnw eclipse:eclipse

The generated eclipse projects can be imported by selecting import existing projects from the file menu.

Appendix B: Contributing

Spring Cloud is released under the non-restrictive Apache 2.0 license, and follows a very standard Github development process, using Github tracker for issues and merging pull requests into master. If you want to contribute even something trivial please do not hesitate, but follow the guidelines below.

B.1. Sign the Contributor License Agreement

Before we accept a non-trivial patch or pull request we will need you to sign the contributor’s agreement. Signing the contributor’s agreement does not grant anyone commit rights to the main repository, but it does mean that we can accept your contributions, and you will get an author credit if we do. Active contributors might be asked to join the core team, and given the ability to merge pull requests.

B.2. Code Conventions and Housekeeping

None of these is essential for a pull request, but they will all help. They can also be added after the original pull request but before a merge.

Use the Spring Framework code format conventions. If you use Eclipse you can import formatter settings using the eclipse-code-formatter.xml file from the Spring Cloud Build project. If using IntelliJ, you can use the Eclipse Code Formatter Plugin to import the same file.
Make sure all new .java files to have a simple Javadoc class comment with at least an @author tag identifying you, and preferably at least a paragraph on what the class is for.
Add the ASF license header comment to all new .java files (copy from existing files in the project)
Add yourself as an @author to the .java files that you modify substantially (more than cosmetic changes).
Add some Javadocs and, if you change the namespace, some XSD doc elements.
A few unit tests would help a lot as well — someone has to do it.
If no-one else is using your branch, please rebase it against the current master (or other target branch in the main project).
When writing a commit message please follow these conventions, if you are fixing an existing issue please add Fixes gh-XXXX at the end of the commit message (where XXXX is the issue number).

Spring Cloud Stream RabbitMQ Binder Reference Guide