3. Reference

This part of the reference documentation details the various components that comprise Spring AMQP. The main chapter covers the core classes to develop an AMQP application. This part also includes a chapter about the sample applications.

3.1 Using Spring AMQP

In this chapter, we will explore the interfaces and classes that are the essential components for developing applications with Spring AMQP.

3.1.1 AMQP Abstractions

Introduction

Spring AMQP consists of a handful of modules, each represented by a JAR in the distribution. These modules are: spring-amqp, and spring-rabbit. The spring-amqp module contains the org.springframework.amqp.core package. Within that package, you will find the classes that represent the core AMQP "model". Our intention is to provide generic abstractions that do not rely on any particular AMQP broker implementation or client library. End user code will be more portable across vendor implementations as it can be developed against the abstraction layer only. These abstractions are then used implemented by broker-specific modules, such as spring-rabbit. There is currently only a RabbitMQ implementation; however the abstractions have been validated in .NET using Apache Qpid in addition to RabbitMQ. Since AMQP operates at the protocol level in principle, the RabbitMQ client can be used with any broker that supports the same protocol version, but we do not test any other brokers at present.

The overview here assumes that you are already familiar with the basics of the AMQP specification. If you are not, then have a look at the resources listed in Chapter 5, Other Resources

Message

The 0-9-1 AMQP specification does not define a Message class or interface. Instead, when performing an operation such as basicPublish(), the content is passed as a byte-array argument and additional properties are passed in as separate arguments. Spring AMQP defines a Message class as part of a more general AMQP domain model representation. The purpose of the Message class is to simply encapsulate the body and properties within a single instance so that the API can in turn be simpler. The Message class definition is quite straightforward.

public class Message {

    private final MessageProperties messageProperties;

    private final byte[] body;

    public Message(byte[] body, MessageProperties messageProperties) {
        this.body = body;
        this.messageProperties = messageProperties;
    }

    public byte[] getBody() {
        return this.body;
    }

    public MessageProperties getMessageProperties() {
        return this.messageProperties;
    }
}

The MessageProperties interface defines several common properties such as messageId, timestamp, contentType, and several more. Those properties can also be extended with user-defined headers by calling the setHeader(String key, Object value) method.

[Important]Important

Starting with versions 1.5.7, 1.6.11, 1.7.4, 2.0.0, if a message body is a serialized Serializable java object, it is no longer deserialized (by default) when performing toString() operations (such as in log messages). This is to prevent unsafe deserialization. By default, only java.util and java.lang classes are deserialized. To revert to the previous behavior, you can add allowable class/package patterns by invoking Message.addWhiteListPatterns(...). A simple * wildcard is supported, for example com.foo.*, *.MyClass. Bodies that cannot be deserialized will be represented by byte[<size>] in log messages.

Exchange

The Exchange interface represents an AMQP Exchange, which is what a Message Producer sends to. Each Exchange within a virtual host of a broker will have a unique name as well as a few other properties:

public interface Exchange {

    String getName();

    String getExchangeType();

    boolean isDurable();

    boolean isAutoDelete();

    Map<String, Object> getArguments();

}

As you can see, an Exchange also has a type represented by constants defined in ExchangeTypes. The basic types are: Direct, Topic, Fanout, and Headers. In the core package you will find implementations of the Exchange interface for each of those types. The behavior varies across these Exchange types in terms of how they handle bindings to Queues. For example, a Direct exchange allows for a Queue to be bound by a fixed routing key (often the Queue’s name). A Topic exchange supports bindings with routing patterns that may include the * and # wildcards for exactly-one and zero-or-more, respectively. The Fanout exchange publishes to all Queues that are bound to it without taking any routing key into consideration. For much more information about these and the other Exchange types, check out Chapter 5, Other Resources.

[Note]Note

The AMQP specification also requires that any broker provide a "default" Direct Exchange that has no name. All Queues that are declared will be bound to that default Exchange with their names as routing keys. You will learn more about the default Exchange’s usage within Spring AMQP in Section 3.1.4, “AmqpTemplate”.

Queue

The Queue class represents the component from which a Message Consumer receives Messages. Like the various Exchange classes, our implementation is intended to be an abstract representation of this core AMQP type.

public class Queue  {

    private final String name;

    private volatile boolean durable;

    private volatile boolean exclusive;

    private volatile boolean autoDelete;

    private volatile Map<String, Object> arguments;

    /**
     * The queue is durable, non-exclusive and non auto-delete.
     *
     * @param name the name of the queue.
     */
    public Queue(String name) {
        this(name, true, false, false);
    }

    // Getters and Setters omitted for brevity

}

Notice that the constructor takes the Queue name. Depending on the implementation, the admin template may provide methods for generating a uniquely named Queue. Such Queues can be useful as a "reply-to" address or other temporary situations. For that reason, the exclusive and autoDelete properties of an auto-generated Queue would both be set to true.

[Note]Note

See the section on queues in Section 3.1.10, “Configuring the broker” for information about declaring queues using namespace support, including queue arguments.

Binding

Given that a producer sends to an Exchange and a consumer receives from a Queue, the bindings that connect Queues to Exchanges are critical for connecting those producers and consumers via messaging. In Spring AMQP, we define a Binding class to represent those connections. Let’s review the basic options for binding Queues to Exchanges.

You can bind a Queue to a DirectExchange with a fixed routing key.

new Binding(someQueue, someDirectExchange, "foo.bar")

You can bind a Queue to a TopicExchange with a routing pattern.

new Binding(someQueue, someTopicExchange, "foo.*")

You can bind a Queue to a FanoutExchange with no routing key.

new Binding(someQueue, someFanoutExchange)

We also provide a BindingBuilder to facilitate a "fluent API" style.

Binding b = BindingBuilder.bind(someQueue).to(someTopicExchange).with("foo.*");
[Note]Note

The BindingBuilder class is shown above for clarity, but this style works well when using a static import for the bind() method.

By itself, an instance of the Binding class is just holding the data about a connection. In other words, it is not an "active" component. However, as you will see later in Section 3.1.10, “Configuring the broker”, Binding instances can be used by the AmqpAdmin class to actually trigger the binding actions on the broker. Also, as you will see in that same section, the Binding instances can be defined using Spring’s @Bean-style within @Configuration classes. There is also a convenient base class which further simplifies that approach for generating AMQP-related bean definitions and recognizes the Queues, Exchanges, and Bindings so that they will all be declared on the AMQP broker upon application startup.

The AmqpTemplate is also defined within the core package. As one of the main components involved in actual AMQP messaging, it is discussed in detail in its own section (see Section 3.1.4, “AmqpTemplate”).

3.1.2 Connection and Resource Management

Introduction

Whereas the AMQP model we described in the previous section is generic and applicable to all implementations, when we get into the management of resources, the details are specific to the broker implementation. Therefore, in this section, we will be focusing on code that exists only within our "spring-rabbit" module since at this point, RabbitMQ is the only supported implementation.

The central component for managing a connection to the RabbitMQ broker is the ConnectionFactory interface. The responsibility of a ConnectionFactory implementation is to provide an instance of org.springframework.amqp.rabbit.connection.Connection which is a wrapper for com.rabbitmq.client.Connection. The only concrete implementation we provide is CachingConnectionFactory which, by default, establishes a single connection proxy that can be shared by the application. Sharing of the connection is possible since the "unit of work" for messaging with AMQP is actually a "channel" (in some ways, this is similar to the relationship between a Connection and a Session in JMS). As you can imagine, the connection instance provides a createChannel method. The CachingConnectionFactory implementation supports caching of those channels, and it maintains separate caches for channels based on whether they are transactional or not. When creating an instance of CachingConnectionFactory, the hostname can be provided via the constructor. The username and password properties should be provided as well. If you would like to configure the size of the channel cache (the default is 25), you could call the setChannelCacheSize() method here as well.

Starting with version 1.3, the CachingConnectionFactory can be configured to cache connections as well as just channels. In this case, each call to createConnection() creates a new connection (or retrieves an idle one from the cache). Closing a connection returns it to the cache (if the cache size has not been reached). Channels created on such connections are cached too. The use of separate connections might be useful in some environments, such as consuming from an HA cluster, in conjunction with a load balancer, to connect to different cluster members. Set the cacheMode to CacheMode.CONNECTION.

[Note]Note

This does not limit the number of connections, it specifies how many idle open connections are allowed.

Starting with version 1.5.5, a new property connectionLimit is provided. When this is set, it limits the total number of connections allowed. When set, if the limit is reached, the channelCheckoutTimeLimit is used to wait for a connection to become idle. If the time is exceeded, an AmqpTimeoutException is thrown.

[Important]Important

When the cache mode is CONNECTION, automatic declaration of queues etc. (See the section called “Automatic Declaration of Exchanges, Queues and Bindings”) is NOT supported.

Also, at the time of writing, the rabbitmq-client library creates a fixed thread pool for each connection (5 threads) by default. When using a large number of connections, you should consider setting a custom executor on the CachingConnectionFactory. Then, the same executor will be used by all connections and its threads can be shared. The executor’s thread pool should be unbounded, or set appropriately for the expected utilization (usually, at least one thread per connection). If multiple channels are created on each connection then the pool size will affect the concurrency, so a variable (or simple cached) thread pool executor would be most suitable.

It is important to understand that the cache size is (by default) not a limit, but merely the number of channels that can be cached. With a cache size of, say, 10, any number of channels can actually be in use. If more than 10 channels are being used and they are all returned to the cache, 10 will go in the cache; the remainder will be physically closed.

Starting with version 1.6, the default channel cache size has been increased from 1 to 25. In high volume, multi-threaded, environments, a small cache means that channels are created and closed at a high rate. Increasing the default cache size will avoid this overhead. You should monitor the channels in use via the RabbitMQ Admin UI and consider increasing the cache size further if you see many channels being created and closed. The cache will only grow on-demand (to suit the concurrency requirements of the application) so this change will not impact existing low-volume applications.

Starting with version 1.4.2, the CachingConnectionFactory has a property channelCheckoutTimeout. When this property is greater than zero, the channelCacheSize becomes a limit on the number of channels that can be created on a connection. If the limit is reached, calling threads will block until a channel is available or this timeout is reached, in which case a AmqpTimeoutException is thrown.

[Warning]Warning

Channels used within the framework (e.g. RabbitTemplate) will be reliably returned to the cache. If you create channels outside of the framework, (e.g. by accessing the connection(s) directly and invoking createChannel()), you must return them (by closing) reliably, perhaps in a finally block, to avoid running out of channels.

CachingConnectionFactory connectionFactory = new CachingConnectionFactory("somehost");
connectionFactory.setUsername("guest");
connectionFactory.setPassword("guest");

Connection connection = connectionFactory.createConnection();

When using XML, the configuration might look like this:

<bean id="connectionFactory"
      class="org.springframework.amqp.rabbit.connection.CachingConnectionFactory">
    <constructor-arg value="somehost"/>
    <property name="username" value="guest"/>
    <property name="password" value="guest"/>
</bean>
[Note]Note

There is also a SingleConnectionFactory implementation which is only available in the unit test code of the framework. It is simpler than CachingConnectionFactory since it does not cache channels, but it is not intended for practical usage outside of simple tests due to its lack of performance and resilience. If you find a need to implement your own ConnectionFactory for some reason, the AbstractConnectionFactory base class may provide a nice starting point.

A ConnectionFactory can be created quickly and conveniently using the rabbit namespace:

<rabbit:connection-factory id="connectionFactory"/>

In most cases this will be preferable since the framework can choose the best defaults for you. The created instance will be a CachingConnectionFactory. Keep in mind that the default cache size for channels is 25. If you want more channels to be cached set a larger value via the channelCacheSize property. In XML it would look like this:

<bean id="connectionFactory"
      class="org.springframework.amqp.rabbit.connection.CachingConnectionFactory">
    <constructor-arg value="somehost"/>
    <property name="username" value="guest"/>
    <property name="password" value="guest"/>
    <property name="channelCacheSize" value="50"/>
</bean>

And with the namespace you can just add the channel-cache-size attribute:

<rabbit:connection-factory
    id="connectionFactory" channel-cache-size="50"/>

The default cache mode is CHANNEL, but you can configure it to cache connections instead; in this case, we use connection-cache-size:

<rabbit:connection-factory
    id="connectionFactory" cache-mode="CONNECTION" connection-cache-size="25"/>

Host and port attributes can be provided using the namespace

<rabbit:connection-factory
    id="connectionFactory" host="somehost" port="5672"/>

Alternatively, if running in a clustered environment, use the addresses attribute.

<rabbit:connection-factory
    id="connectionFactory" addresses="host1:5672,host2:5672"/>

Here’s an example with a custom thread factory that prefixes thread names with rabbitmq-.

<rabbit:connection-factory id="multiHost" virtual-host="/bar" addresses="host1:1234,host2,host3:4567"
    thread-factory="tf"
    channel-cache-size="10" username="user" password="password" />

<bean id="tf" class="org.springframework.scheduling.concurrent.CustomizableThreadFactory">
    <constructor-arg value="rabbitmq-" />
</bean>

Starting with version 2.0 a ConnectionNameStrategy is provided for the injection into the AbstractionConnectionFactory. The generated name is used for the application-specific identification of the target RabbitMQ connection. The connection name is displayed in the management UI if RabbitMQ server supports it. This value doesn’t have to be unique and cannot be used as a connection identifier e.g. in HTTP API requests. This value is supposed to be human-readable and is a part of ClientProperties under connection_name key. Can be used as a simple Lambda:

connectionFactory.setConnectionNameStrategy(connectionFactory -> "MY_CONNECTION");

The ConnectionFactory argument can be used to distinguish target connection names by some logic. By default a beanName of the AbstractConnectionFactory and an internal counter are used to generate connection_name. The <rabbit:connection-factory> namespace component is also supplied with the connection-name-strategy attribute.

The connection might be blocked for interaction from the Broker according to the Memory Alarm. Starting with version 2.0, the org.springframework.amqp.rabbit.connection.Connection can be supplied with com.rabbitmq.client.BlockedListener s to to be notified for connection blocked and unblocked events. In addition the AbstractConnectionFactory emits a ConnectionBlockedEvent and ConnectionUnblockedEvent, respectively, via its internal BlockedListener implementation. These allow you to provide application logic to react appropriately to problems on the broker and take some corrective actions for example.

[Important]Important

When the application is configured with a single CachingConnectionFactory, as it is by default with Spring Boot auto-configuration, the application will stop working when the connection is blocked by the Broker. And when it is blocked by the Broker, any its clients stop to work. If we have producers and consumers in the same application, we may end up with a deadlock when producers are blocking the connection because there are no resources on the Broker anymore and consumers can’t free them because the connection is blocked. To mitigate the problem, there is just enough to have one more separate CachingConnectionFactory instance with the same options - one for producers and one for consumers. The separate CachingConnectionFactory isn’t recommended for transactional producers, since they should reuse a Channel associated with the consumer transactions.

Configuring the Underlying Client Connection Factory

The CachingConnectionFactory uses an instance of the Rabbit client ConnectionFactory; a number of configuration properties are passed through (host, port, userName, password, requestedHeartBeat, connectionTimeout for example) when setting the equivalent property on the CachingConnectionFactory. To set other properties (clientProperties for example), define an instance of the rabbit factory and provide a reference to it using the appropriate constructor of the CachingConnectionFactory. When using the namespace as described above, provide a reference to the configured factory in the connection-factory attribute. For convenience, a factory bean is provided to assist in configuring the connection factory in a Spring application context, as discussed in the next section.

<rabbit:connection-factory
      id="connectionFactory" connection-factory="rabbitConnectionFactory"/>
[Note]Note

The 4.0.x client enables automatic recovery by default; while compatible with this feature, Spring AMQP has its own recovery mechanisms and the client recovery feature generally isn’t needed. It is recommended to disable amqp-client automatic recovery, to avoid getting AutoRecoverConnectionNotCurrentlyOpenException s when the broker is available, but the connection has not yet recovered. You may notice this exception, for example, when a RetryTemplate is configured in a RabbitTemplate, even when failing over to another broker in a cluster. Since the auto recovering connection recovers on a timer, the connection may be recovered faster using Spring AMQP’s recovery mechanisms. Starting with version 1.7.1, Spring AMQP disables it unless you explicitly create your own RabbitMQ connection factory and provide it to the CachingConnectionFactory. RabbitMQ ConnectionFactory instances created by the RabbitConnectionFactoryBean will also have the option disabled by default.

RabbitConnectionFactoryBean and Configuring SSL

Starting with version 1.4, a convenient RabbitConnectionFactoryBean is provided to enable convenient configuration of SSL properties on the underlying client connection factory, using dependency injection. Other setters simply delegate to the underlying factory. Previously you had to configure the SSL options programmatically.

<rabbit:connection-factory id="rabbitConnectionFactory"
    connection-factory="clientConnectionFactory"
    host="${host}"
    port="${port}"
    virtual-host="${vhost}"
    username="${username}" password="${password}" />

<bean id="clientConnectionFactory"
        class="org.springframework.xd.dirt.integration.rabbit.RabbitConnectionFactoryBean">
    <property name="useSSL" value="true" />
    <property name="sslPropertiesLocation" value="file:/secrets/rabbitSSL.properties"/>
</bean>

Refer to the RabbitMQ Documentation for information about configuring SSL. Omit the keyStore and trustStore configuration to connect over SSL without certificate validation. Key and trust store configuration can be provided as follows:

The sslPropertiesLocation property is a Spring Resource pointing to a properties file containing the following keys:

keyStore=file:/secret/keycert.p12
trustStore=file:/secret/trustStore
keyStore.passPhrase=secret
trustStore.passPhrase=secret

The keyStore and truststore are Spring Resources pointing to the stores. Typically this properties file will be secured by the operating system with the application having read access.

Starting with Spring AMQP version 1.5, these properties can be set directly on the factory bean. If both discrete properties and sslPropertiesLocation is provided, properties in the latter will override the discrete values.

Routing Connection Factory

Starting with version 1.3, the AbstractRoutingConnectionFactory has been introduced. This provides a mechanism to configure mappings for several ConnectionFactories and determine a target ConnectionFactory by some lookupKey at runtime. Typically, the implementation checks a thread-bound context. For convenience, Spring AMQP provides the SimpleRoutingConnectionFactory, which gets the current thread-bound lookupKey from the SimpleResourceHolder:

<bean id="connectionFactory"
      class="org.springframework.amqp.rabbit.connection.SimpleRoutingConnectionFactory">
	<property name="targetConnectionFactories">
		<map>
			<entry key="#{connectionFactory1.virtualHost}" ref="connectionFactory1"/>
			<entry key="#{connectionFactory2.virtualHost}" ref="connectionFactory2"/>
		</map>
	</property>
</bean>

<rabbit:template id="template" connection-factory="connectionFactory" />
public class MyService {

    @Autowired
    private RabbitTemplate rabbitTemplate;

    public void service(String vHost, String payload) {
        SimpleResourceHolder.bind(rabbitTemplate.getConnectionFactory(), vHost);
        rabbitTemplate.convertAndSend(payload);
        SimpleResourceHolder.unbind(rabbitTemplate.getConnectionFactory());
    }

}

It is important to unbind the resource after use. For more information see the JavaDocs of AbstractRoutingConnectionFactory.

Starting with version 1.4, the RabbitTemplate supports the SpEL sendConnectionFactorySelectorExpression and receiveConnectionFactorySelectorExpression properties, which are evaluated on each AMQP protocol interaction operation (send, sendAndReceive, receive or receiveAndReply), resolving to a lookupKey value for the provided AbstractRoutingConnectionFactory. Bean references, such as "@vHostResolver.getVHost(#root)" can be used in the expression. For send operations, the Message to be sent is the root evaluation object; for receive operations, the queueName is the root evaluation object.

The routing algorithm is: If the selector expression is null, or is evaluated to null, or the provided ConnectionFactory isn’t an instance of AbstractRoutingConnectionFactory, everything works as before, relying on the provided ConnectionFactory implementation. The same occurs if the evaluation result isn’t null, but there is no target ConnectionFactory for that lookupKey and the AbstractRoutingConnectionFactory is configured with lenientFallback = true. Of course, in the case of an AbstractRoutingConnectionFactory it does fallback to its routing implementation based on determineCurrentLookupKey(). But, if lenientFallback = false, an IllegalStateException is thrown.

The Namespace support also provides the send-connection-factory-selector-expression and receive-connection-factory-selector-expression attributes on the <rabbit:template> component.

Also starting with version 1.4, you can configure a routing connection factory in a listener container. In that case, the list of queue names is used as the lookup key. For example, if you configure the container with setQueueNames("foo", "bar"), the lookup key will be "[foo,bar]" (no spaces).

Starting with version 1.6.9 you can add a qualifier to the lookup key using setLookupKeyQualifier on the listener container. This would enable, for example, listening to queues with the same name, but in different virtual host (where you would have a connection factory for each).

For example, with lookup key qualifier foo and a container listening to queue bar, the lookup key you would register the target connection factory with would be foo[bar].

Queue Affinity and the LocalizedQueueConnectionFactory

When using HA queues in a cluster, for the best performance, it can be desirable to connect to the physical broker where the master queue resides. While the CachingConnectionFactory can be configured with multiple broker addresses; this is to fail over and the client will attempt to connect in order. The LocalizedQueueConnectionFactory uses the REST API provided by the admin plugin to determine which node the queue is mastered. It then creates (or retrieves from a cache) a CachingConnectionFactory that will connect to just that node. If the connection fails, the new master node is determined and the consumer connects to it. The LocalizedQueueConnectionFactory is configured with a default connection factory, in case the physical location of the queue cannot be determined, in which case it will connect as normal to the cluster.

The LocalizedQueueConnectionFactory is a RoutingConnectionFactory and the SimpleMessageListenerContainer uses the queue names as the lookup key as discussed in the section called “Routing Connection Factory” above.

[Note]Note

For this reason (the use of the queue name for the lookup), the LocalizedQueueConnectionFactory can only be used if the container is configured to listen to a single queue.

[Note]Note

The RabbitMQ management plugin must be enabled on each node.

[Caution]Caution

This connection factory is intended for long-lived connections, such as those used by the SimpleMessageListenerContainer. It is not intended for short connection use, such as with a RabbitTemplate because of the overhead of invoking the REST API before making the connection. Also, for publish operations, the queue is unknown, and the message is published to all cluster members anyway, so the logic of looking up the node has little value.

Here is an example configuration, using Spring Boot’s RabbitProperties to configure the factories:

@Autowired
private RabbitProperties props;

private final String[] adminUris = { "http://host1:15672", "http://host2:15672" };

private final String[] nodes = { "[email protected]", "[email protected]" };

@Bean
public ConnectionFactory defaultConnectionFactory() {
    CachingConnectionFactory cf = new CachingConnectionFactory();
    cf.setAddresses(this.props.getAddresses());
    cf.setUsername(this.props.getUsername());
    cf.setPassword(this.props.getPassword());
    cf.setVirtualHost(this.props.getVirtualHost());
    return cf;
}

@Bean
public ConnectionFactory queueAffinityCF(
        @Qualifier("defaultConnectionFactory") ConnectionFactory defaultCF) {
    return new LocalizedQueueConnectionFactory(defaultCF,
            StringUtils.commaDelimitedListToStringArray(this.props.getAddresses()),
            this.adminUris, this.nodes,
            this.props.getVirtualHost(), this.props.getUsername(), this.props.getPassword(),
            false, null);
}

Notice that the first three parameters are arrays of addresses, adminUris and nodes. These are positional in that when a container attempts to connect to a queue, it determines on which node the queue is mastered and connects to the address in the same array position.

Publisher Confirms and Returns

Confirmed and returned messages are supported by setting the CachingConnectionFactory's publisherConfirms and publisherReturns properties to 'true' respectively.

When these options are set, Channel s created by the factory are wrapped in an PublisherCallbackChannel, which is used to facilitate the callbacks. When such a channel is obtained, the client can register a PublisherCallbackChannel.Listener with the Channel. The PublisherCallbackChannel implementation contains logic to route a confirm/return to the appropriate listener. These features are explained further in the following sections.

[Tip]Tip

For some more background information, please see the following blog post by the RabbitMQ team titled Introducing Publisher Confirms.

Connection and Channel Listeners

The connection factory supports registering ConnectionListener and ChannelListener implementations. This allows you to receive notifications for connection and channel related events. (A ConnectionListener is used by the RabbitAdmin to perform declarations when the connection is established - see the section called “Automatic Declaration of Exchanges, Queues and Bindings” for more information).

ConnectionListener. 

@FunctionalInterface
public interface ConnectionListener {

    void onCreate(Connection connection);

    default void onClose(Connection connection) {
    }

    default void onShutDown(ShutdownSignalException signal) {
    }

}

Starting with version 2.0, the org.springframework.amqp.rabbit.connection.Connection object can be supplied with com.rabbitmq.client.BlockedListener s to to be notified for connection blocked and unblocked events.

ChannelListener. 

@FunctionalInterface
public interface ChannelListener {

    void onCreate(Channel channel, boolean transactional);

    default void onShutDown(ShutdownSignalException signal) {
    }

}

See the section called “Publishing is Asynchronous - How to Detect Success and Failures” for one scenario where you might want to register a ChannelListener.

Logging Channel Close Events

A mechanism to enable users to control logging levels was introduced in version 1.5.

The CachingConnectionFactory uses a default strategy to log channel closures as follows:

  • Normal channel closes (200 OK) are not logged.
  • If a channel is closed due to a failed passive queue declaration, it is logged at debug level.
  • If a channel is closed because the basic.consume is refused due to an exclusive consumer condition, it is logged at INFO level.
  • All others are logged at ERROR level.

To modify this behavior, inject a custom ConditionalExceptionLogger into the CachingConnectionFactory in its closeExceptionLogger property.

Also see the section called “Consumer Failure Events”.

Runtime Cache Properties

Staring with version 1.6, the CachingConnectionFactory now provides cache statistics via the getCacheProperties() method. These statistics can be used to tune the cache to optimize it in production. For example, the high water marks can be used to determine whether the cache size should be increased. If it equals the cache size, you might want to consider increasing further.

Table 3.1. Cache properties for CacheMode.CHANNEL

PropertyMeaning
connectionName

The name of the connection generated by the ConnectionNameStrategy.

channelCacheSize

The currently configured maximum channels that are allowed to be idle.

localPort

The local port for the connection (if available). This can be used to correlate with connections/channels on the RabbitMQ Admin UI.

idleChannelsTx

The number of transactional channels that are currently idle (cached).

idleChannelsNotTx

The number of non-transactional channels that are currently idle (cached).

idleChannelsTxHighWater

The maximum number of transactional channels that have been concurrently idle (cached).

idleChannelsNotTxHighWater

The maximum number of non-transactional channels have been concurrently idle (cached).


Table 3.2. Cache properties for CacheMode.CONNECTION

PropertyMeaning
connectionName:<localPort>

The name of the connection generated by the ConnectionNameStrategy.

openConnections

The number of connection objects representing connections to brokers.

channelCacheSize

The currently configured maximum channels that are allowed to be idle.

connectionCacheSize

The currently configured maximum connections that are allowed to be idle.

idleConnections

The number of connections that are currently idle.

idleConnectionsHighWater

The maximum number of connections that have been concurrently idle.

idleChannelsTx:<localPort>

The number of transactional channels that are currently idle (cached) for this connection. The localPort part of the property name can be used to correlate with connections/channels on the RabbitMQ Admin UI.

idleChannelsNotTx:<localPort>

The number of non-transactional channels that are currently idle (cached) for this connection. The localPort part of the property name can be used to correlate with connections/channels on the RabbitMQ Admin UI.

idleChannelsTxHighWater:
<localPort>

The maximum number of transactional channels that have been concurrently idle (cached). The localPort part of the property name can be used to correlate with connections/channels on the RabbitMQ Admin UI.

idleChannelsNotTxHighWater:
<localPort>

The maximum number of non-transactional channels have been concurrently idle (cached). The localPort part of the property name can be used to correlate with connections/channels on the RabbitMQ Admin UI.


The cacheMode property (CHANNEL or CONNECTION is also included).

Figure 3.1. JVisualVM Example

cacheStats

RabbitMQ Automatic Connection/Topology recovery

Since the first version of Spring AMQP, the framework has provided its own connection and channel recovery in the event of a broker failure. Also, as discussed in Section 3.1.10, “Configuring the broker”, the RabbitAdmin will re-declare any infrastructure beans (queues etc) when the connection is re-established. It therefore does not rely on the Auto Recovery that is now provided by the amqp-client library. Spring AMQP now uses the 4.0.x version of amqp-client, which has auto recovery enabled by default. Spring AMQP can still use its own recovery mechanisms if you wish, disabling it in the client, (by setting the automaticRecoveryEnabled property on the underlying RabbitMQ connectionFactory to false). However, the framework is completely compatible with auto recovery being enabled. This means any consumers you create within your code (perhaps via RabbitTemplate.execute()) can be recovered automatically.

3.1.3 Adding Custom Client Connection Properties

The CachingConnectionFactory now allows you to access the underlying connection factory to allow, for example, setting custom client properties:

connectionFactory.getRabbitConnectionFactory().getClientProperties().put("foo", "bar");

These properties appear in the RabbitMQ Admin UI when viewing the connection.

3.1.4 AmqpTemplate

Introduction

As with many other high-level abstractions provided by the Spring Framework and related projects, Spring AMQP provides a "template" that plays a central role. The interface that defines the main operations is called AmqpTemplate. Those operations cover the general behavior for sending and receiving Messages. In other words, they are not unique to any implementation, hence the "AMQP" in the name. On the other hand, there are implementations of that interface that are tied to implementations of the AMQP protocol. Unlike JMS, which is an interface-level API itself, AMQP is a wire-level protocol. The implementations of that protocol provide their own client libraries, so each implementation of the template interface will depend on a particular client library. Currently, there is only a single implementation: RabbitTemplate. In the examples that follow, you will often see usage of an "AmqpTemplate", but when you look at the configuration examples, or any code excerpts where the template is instantiated and/or setters are invoked, you will see the implementation type (e.g. "RabbitTemplate").

As mentioned above, the AmqpTemplate interface defines all of the basic operations for sending and receiving Messages. We will explore Message sending and reception, respectively, in the two sections that follow.

See also the section called “AsyncRabbitTemplate”.

Adding Retry Capabilities

Starting with version 1.3 you can now configure the RabbitTemplate to use a RetryTemplate to help with handling problems with broker connectivity. Refer to the spring-retry project for complete information; the following is just one example that uses an exponential back off policy and the default SimpleRetryPolicy which will make three attempts before throwing the exception to the caller.

Using the XML namespace:

<rabbit:template id="template" connection-factory="connectionFactory" retry-template="retryTemplate"/>

<bean id="retryTemplate" class="org.springframework.retry.support.RetryTemplate">
    <property name="backOffPolicy">
        <bean class="org.springframework.retry.backoff.ExponentialBackOffPolicy">
            <property name="initialInterval" value="500" />
            <property name="multiplier" value="10.0" />
            <property name="maxInterval" value="10000" />
        </bean>
    </property>
</bean>

Using @Configuration:

@Bean
public AmqpTemplate rabbitTemplate();
    RabbitTemplate template = new RabbitTemplate(connectionFactory());
    RetryTemplate retryTemplate = new RetryTemplate();
    ExponentialBackOffPolicy backOffPolicy = new ExponentialBackOffPolicy();
    backOffPolicy.setInitialInterval(500);
    backOffPolicy.setMultiplier(10.0);
    backOffPolicy.setMaxInterval(10000);
    retryTemplate.setBackOffPolicy(backOffPolicy);
    template.setRetryTemplate(retryTemplate);
    return template;
}

Starting with version 1.4, in addition to the retryTemplate property, the recoveryCallback option is supported on the RabbitTemplate. It is used as a second argument for the RetryTemplate.execute(RetryCallback<T, E> retryCallback, RecoveryCallback<T>recoveryCallback).

[Note]Note

The RecoveryCallback is somewhat limited in that the retry context only contains the lastThrowable field. For more sophisticated use cases, you should use an external RetryTemplate so that you can convey additional information to the RecoveryCallback via the context’s attributes:

retryTemplate.execute(
    new RetryCallback<Object, Exception>() {

        @Override
        public Object doWithRetry(RetryContext context) throws Exception {
            context.setAttribute("message", message);
            return rabbitTemplate.convertAndSend(exchange, routingKey, message);
        }

    }, new RecoveryCallback<Object>() {

        @Override
        public Object recover(RetryContext context) throws Exception {
            Object message = context.getAttribute("message");
            Throwable t = context.getLastThrowable();
            // Do something with message
            return null;
        }
    });
}

In this case, you would not inject a RetryTemplate into the RabbitTemplate.

Publishing is Asynchronous - How to Detect Success and Failures

Publishing messages is an asynchronous mechanism and, by default, messages that can’t be routed are simply dropped by RabbitMQ. For successful publishing you can receive an async confirmation as described in the section called “Publisher Confirms and Returns” below. Let’s consider two failure scenarios:

  • publish to an exchange but there is no matching destination queue
  • publish to a non-existent exchange

The first case is covered by publisher returns as described in the section called “Publisher Confirms and Returns” below.

For the second case, the message is dropped, no return is generated; the underlying channel is closed with an exception. By default, this exception is logged, but you can register a ChannelListener with the CachingConnectionFactory to obtain notifications of such events:

this.connectionFactory.addConnectionListener(new ConnectionListener() {

    @Override
    public void onCreate(Connection connection) {
    }

    @Override
    public void onShutDown(ShutdownSignalException signal) {
        ...
    }

});

You can examine the signal’s reason property to determine the problem that occurred.

To detect the exception on the sending thread, you can setChannelTransacted(true) on the RabbitTemplate and the exception will be detected on the txCommit(). However, transactions significantly impede performance so consider this carefully before enabling transactions for just this one use case.

Publisher Confirms and Returns

The RabbitTemplate implementation of AmqpTemplate supports Publisher Confirms and Returns.

For returned messages, the template’s mandatory property must be set to true, or the mandatory-expression must evaluate to true for a particular message. This feature requires a CachingConnectionFactory that has its publisherReturns property set to true (see the section called “Publisher Confirms and Returns”). Returns are sent to to the client by it registering a RabbitTemplate.ReturnCallback by calling setReturnCallback(ReturnCallback callback). The callback must implement this method:

void returnedMessage(Message message, int replyCode, String replyText,
          String exchange, String routingKey);

Only one ReturnCallback is supported by each RabbitTemplate. See also the section called “Reply Timeout”.

For Publisher Confirms (aka Publisher Acknowledgements), the template requires a CachingConnectionFactory that has its publisherConfirms property set to true. Confirms are sent to to the client by it registering a RabbitTemplate.ConfirmCallback by calling setConfirmCallback(ConfirmCallback callback). The callback must implement this method:

void confirm(CorrelationData correlationData, boolean ack, String cause);

The CorrelationData is an object supplied by the client when sending the original message. The ack is true for an ack and false for a nack. For nack s, the cause may contain a reason for the nack, if it is available when the nack is generated. An example is when sending a message to a non-existent exchange. In that case the broker closes the channel; the reason for the closure is included in the cause. cause was added in version 1.4.

Only one ConfirmCallback is supported by a RabbitTemplate.

[Note]Note

When a rabbit template send operation completes, the channel is closed; this would preclude the reception of confirms or returns in the case when the connection factory cache is full (when there is space in the cache, the channel is not physically closed and the returns/confirms will proceed as normal). When the cache is full, the framework defers the close for up to 5 seconds, in order to allow time for the confirms/returns to be received. When using confirms, the channel will be closed when the last confirm is received. When using only returns, the channel will remain open for the full 5 seconds. It is generally recommended to set the connection factory’s channelCacheSize to a large enough value so that the channel on which a message is published is returned to the cache instead of being closed. You can monitor channel usage using the RabbitMQ management plugin; if you see channels being opened/closed rapidly you should consider increasing the cache size to reduce overhead on the server.

See also the section called “Scoped Operations” for a simpler mechanism for waiting for publisher confirms.

Scoped Operations

Normally, when using the template, a Channel is checked out of the cache (or created), used for the operation, and returned to the cache for reuse. In a multi-threaded environment, there is no guarantee that the next operation will use the same channel. There may be times, however, where you want to have more control over the use of a channel, and ensure that a number of operations are all performed on the same channel.

Starting with version 2.0, a new method invoke is provided, with an OperationsCallback. Any operations performed within the scope of the callback, and on the provided RabbitOperations argument, will use the same dedicated Channel, which will be closed at the end (not returned to a cache).

@FunctionalInterface
public interface OperationsCallback<T> {

    T doInRabbit(RabbitOperations operations);

}

One example of why you might need this is if you wish to use the waitForConfirms() method on the underlying Channel. This method was not previously exposed using the Spring API because the channel is, generally, cached and shared as discussed above. The RabbitTemplate now provides waitForConfirms(long timeout) and waitForConfirmsOrDie(long timeout) which delegate to the dedicated channel used within the scope of the OperationsCallback. The methods cannot be used outside of that scope, for obvious reasons.

Note that a higher-level abstraction which allows you to correlate confirms to requests is provided elsewhere (see the section called “Publisher Confirms and Returns”). You still need to set the connection factory’s publisherConfirms property to true as discussed in that section, but for simple use cases where you just want to wait until all confirms are received, you can use this technique here:

Collection<?> messages = getMessagesToSend();
Boolean result = this.template.invoke(t -> {
    messages.forEach(m -> t.convertAndSend(ROUTE, m));
    t.waitForConfirmsOrDie(10_000);
    return true;
});

If you wish RabbitAdmin operations to be invoked on the same channel, within the scope of the OperationsCallback, the admin must have been constructed using the same RabbitTemplate that was used for the invoke operation.

[Note]Note

The above discussion is moot if the template operations are already performed within the scope of an existing transaction. For example, when running on a transacted listener container thread and performing operations on a transacted template. In that case, the operations will be performed on that channel and committed when the thread returns to the container; it is not necessary to use invoke in that scenario.

Messaging integration

Starting with version 1.4 RabbitMessagingTemplate, built on top of RabbitTemplate, provides an integration with the Spring Framework messaging abstraction, i.e. org.springframework.messaging.Message. This allows you to send and receive messages using the spring-messaging Message<?> abstraction. This abstraction is used by other Spring projects such as Spring Integration and Spring’s STOMP support. There are two message converters involved; one to convert between a spring-messaging Message<?> and Spring AMQP’s Message abstraction, and one to convert between Spring AMQP’s Message abstraction and the format required by the underlying RabbitMQ client library. By default, the message payload is converted by the provided RabbitTemplate 's message converter. Alternatively, you can inject a custom MessagingMessageConverter with some other payload converter:

MessagingMessageConverter amqpMessageConverter = new MessagingMessageConverter();
amqpMessageConverter.setPayloadConverter(myPayloadConverter);
rabbitMessagingTempalte.setAmqpMessageConverter(amqpMessageConverter);

Validated User Id

Starting with version 1.6, the template now supports a user-id-expression (userIdExpression when using Java configuration). If a message is sent, the user id property is set (if not already set) after evaluating this expression. The root object for the evaluation is the message to be sent.

Examples:

<rabbit:template ... user-id-expression="'guest'" />

<rabbit:template ... user-id-expression="@myConnectionFactory.username" />

The first example is a literal expression; the second obtains the username property from a connection factory bean in the application context.

3.1.5 Sending messages

Introduction

When sending a Message, one can use any of the following methods:

void send(Message message) throws AmqpException;

void send(String routingKey, Message message) throws AmqpException;

void send(String exchange, String routingKey, Message message) throws AmqpException;

We can begin our discussion with the last method listed above since it is actually the most explicit. It allows an AMQP Exchange name to be provided at runtime along with a routing key. The last parameter is the callback that is responsible for actual creating of the Message instance. An example of using this method to send a Message might look this this:

amqpTemplate.send("marketData.topic", "quotes.nasdaq.FOO",
    new Message("12.34".getBytes(), someProperties));

The "exchange" property can be set on the template itself if you plan to use that template instance to send to the same exchange most or all of the time. In such cases, the second method listed above may be used instead. The following example is functionally equivalent to the previous one:

amqpTemplate.setExchange("marketData.topic");
amqpTemplate.send("quotes.nasdaq.FOO", new Message("12.34".getBytes(), someProperties));

If both the "exchange" and "routingKey" properties are set on the template, then the method accepting only the Message may be used:

amqpTemplate.setExchange("marketData.topic");
amqpTemplate.setRoutingKey("quotes.nasdaq.FOO");
amqpTemplate.send(new Message("12.34".getBytes(), someProperties));

A better way of thinking about the exchange and routing key properties is that the explicit method parameters will always override the template’s default values. In fact, even if you do not explicitly set those properties on the template, there are always default values in place. In both cases, the default is an empty String, but that is actually a sensible default. As far as the routing key is concerned, it’s not always necessary in the first place (e.g. a Fanout Exchange). Furthermore, a Queue may be bound to an Exchange with an empty String. Those are both legitimate scenarios for reliance on the default empty String value for the routing key property of the template. As far as the Exchange name is concerned, the empty String is quite commonly used because the AMQP specification defines the "default Exchange" as having no name. Since all Queues are automatically bound to that default Exchange (which is a Direct Exchange) using their name as the binding value, that second method above can be used for simple point-to-point Messaging to any Queue through the default Exchange. Simply provide the queue name as the "routingKey" - either by providing the method parameter at runtime:

RabbitTemplate template = new RabbitTemplate(); // using default no-name Exchange
template.send("queue.helloWorld", new Message("Hello World".getBytes(), someProperties));

Or, if you prefer to create a template that will be used for publishing primarily or exclusively to a single Queue, the following is perfectly reasonable:

RabbitTemplate template = new RabbitTemplate(); // using default no-name Exchange
template.setRoutingKey("queue.helloWorld"); // but we'll always send to this Queue
template.send(new Message("Hello World".getBytes(), someProperties));

Message Builder API

Starting with version 1.3, a message builder API is provided by the MessageBuilder and MessagePropertiesBuilder; they provides a convenient "fluent" means of creating a message or message properties:

Message message = MessageBuilder.withBody("foo".getBytes())
    .setContentType(MessageProperties.CONTENT_TYPE_TEXT_PLAIN)
    .setMessageId("123")
    .setHeader("bar", "baz")
    .build();

or

MessageProperties props = MessagePropertiesBuilder.newInstance()
    .setContentType(MessageProperties.CONTENT_TYPE_TEXT_PLAIN)
    .setMessageId("123")
    .setHeader("bar", "baz")
    .build();
Message message = MessageBuilder.withBody("foo".getBytes())
    .andProperties(props)
    .build();

Each of the properties defined on the MessageProperties can be set. Other methods include setHeader(String key, String value), removeHeader(String key), removeHeaders(), and copyProperties(MessageProperties properties). Each property setting method has a set*IfAbsent() variant. In the cases where a default initial value exists, the method is named set*IfAbsentOrDefault().

Five static methods are provided to create an initial message builder:

public static MessageBuilder withBody(byte[] body) 1

public static MessageBuilder withClonedBody(byte[] body) 2

public static MessageBuilder withBody(byte[] body, int from, int to) 3

public static MessageBuilder fromMessage(Message message) 4

public static MessageBuilder fromClonedMessage(Message message) 5

1

The message created by the builder will have a body that is a direct reference to the argument.

2

The message created by the builder will have a body that is a new array containing a copy of bytes in the argument.

3

The message created by the builder will have a body that is a new array containing the range of bytes from the argument. See Arrays.copyOfRange() for more details.

4

The message created by the builder will have a body that is a direct reference to the body of the argument. The argument’s properties are copied to a new MessageProperties object.

5

The message created by the builder will have a body that is a new array containing a copy of the argument’s body. The argument’s properties are copied to a new MessageProperties object.

public static MessagePropertiesBuilder newInstance() 1

public static MessagePropertiesBuilder fromProperties(MessageProperties properties) 2

public static MessagePropertiesBuilder fromClonedProperties(MessageProperties properties) 3

1

A new message properties object is initialized with default values.

2

The builder is initialized with, and build() will return, the provided properties object.,

3

The argument’s properties are copied to a new MessageProperties object.

With the RabbitTemplate implementation of AmqpTemplate, each of the send() methods has an overloaded version that takes an additional CorrelationData object. When publisher confirms are enabled, this object is returned in the callback described in Section 3.1.4, “AmqpTemplate”. This allows the sender to correlate a confirm (ack or nack) with the sent message.

Starting with version 1.6.7, the CorrelationAwareMessagePostProcessor interface was introduced, allowing the correlation data to be modified after the message has been converted:

Message postProcessMessage(Message message, Correlation correlation);

In version 2.0, this interface is deprecated; the method has been moved to MessagePostProcessor with a default implementation that delegates to postProcessMessage(Message message).

Also starting with version 1.6.7 a new callback interface is provided CorrelationDataPostProcessor; this is invoked after all MessagePostProcessor s (provided in the send() method as well as those provided in setBeforePublishPostProcessors()). Implementations can update or replace the correlation data supplied in the send() method (if any). The Message and original CorrelationData (if any) are provided as arguments.

CorrelationData postProcess(Message message, CorrelationData correlationData);

Publisher Returns

When the template’s mandatory property is true returned messages are provided by the callback described in Section 3.1.4, “AmqpTemplate”.

Starting with version 1.4 the RabbitTemplate supports the SpEL mandatoryExpression property, which is evaluated against each request message, as the root evaluation object, resolving to a boolean value. Bean references, such as "@myBean.isMandatory(#root)" can be used in the expression.

Publisher returns can also be used internally by the RabbitTemplate in send and receive operations. See the section called “Reply Timeout” for more information.

Batching

Starting with version 1.4.2, the BatchingRabbitTemplate has been introduced. This is a subclass of RabbitTemplate with an overridden send method that batches messages according to the BatchingStrategy; only when a batch is complete is the message sent to RabbitMQ.

public interface BatchingStrategy {

	MessageBatch addToBatch(String exchange, String routingKey, Message message);

	Date nextRelease();

	Collection<MessageBatch> releaseBatches();

}
[Caution]Caution

Batched data is held in memory; unsent messages can be lost in the event of a system failure.

A SimpleBatchingStrategy is provided. It supports sending messages to a single exchange/routing key. It has properties:

  • batchSize - the number of messages in a batch before it is sent
  • bufferLimit - the maximum size of the batched message; this will preempt the batchSize if exceeded, and cause a partial batch to be sent
  • timeout - a time after which a partial batch will be sent when there is no new activity adding messages to the batch

The SimpleBatchingStrategy formats the batch by preceding each embedded message with a 4 byte binary length. This is communicated to the receiving system by setting the springBatchFormat message property to lengthHeader4.

[Important]Important

Batched messages are automatically de-batched by listener containers (using the springBatchFormat message header). Rejecting any message from a batch will cause the entire batch to be rejected.

3.1.6 Receiving messages

Introduction

Message reception is always a little more complicated than sending. There are two ways to receive a Message. The simpler option is to poll for a single Message at a time with a polling method call. The more complicated yet more common approach is to register a listener that will receive Messages on-demand, asynchronously. We will look at an example of each approach in the next two sub-sections.

Polling Consumer

The AmqpTemplate itself can be used for polled Message reception. By default, if no message is available, null is returned immediately; there is no blocking. Starting with version 1.5, you can now set a receiveTimeout, in milliseconds, and the receive methods will block for up to that long, waiting for a message. A value less than zero means block indefinitely (or at least until the connection to the broker is lost). Version 1.6 introduced variants of the receive methods allowing the timeout to be passed in on each call.

[Caution]Caution

Since the receive operation creates a new QueueingConsumer for each message, this technique is not really appropriate for high-volume environments; consider using an asynchronous consumer, or a receiveTimeout of zero for those use cases.

There are four simple receive methods available. As with the Exchange on the sending side, there is a method that requires a default queue property having been set directly on the template itself, and there is a method that accepts a queue parameter at runtime. Version 1.6 introduced variants to accept timeoutMillis to override receiveTimeout on a per-request basis.

Message receive() throws AmqpException;

Message receive(String queueName) throws AmqpException;

Message receive(long timeoutMillis) throws AmqpException;

Message receive(String queueName, long timeoutMillis) throws AmqpException;

Just like in the case of sending messages, the AmqpTemplate has some convenience methods for receiving POJOs instead of Message instances, and implementations will provide a way to customize the MessageConverter used to create the Object returned:

Object receiveAndConvert() throws AmqpException;

Object receiveAndConvert(String queueName) throws AmqpException;

Message receiveAndConvert(long timeoutMillis) throws AmqpException;

Message receiveAndConvert(String queueName, long timeoutMillis) throws AmqpException;

Starting with version 2.0, there are variants of these methods that take an additional ParameterizedTypeReference argument to convert complex types. The template must be configured with a SmartMessageConverter; see the section called “Converting From a Message With RabbitTemplate” for more information.

Similar to sendAndReceive methods, beginning with version 1.3, the AmqpTemplate has several convenience receiveAndReply methods for synchronously receiving, processing and replying to messages:

<R, S> boolean receiveAndReply(ReceiveAndReplyCallback<R, S> callback)
	   throws AmqpException;

<R, S> boolean receiveAndReply(String queueName, ReceiveAndReplyCallback<R, S> callback)
 	throws AmqpException;

<R, S> boolean receiveAndReply(ReceiveAndReplyCallback<R, S> callback,
	String replyExchange, String replyRoutingKey) throws AmqpException;

<R, S> boolean receiveAndReply(String queueName, ReceiveAndReplyCallback<R, S> callback,
	String replyExchange, String replyRoutingKey) throws AmqpException;

<R, S> boolean receiveAndReply(ReceiveAndReplyCallback<R, S> callback,
 	ReplyToAddressCallback<S> replyToAddressCallback) throws AmqpException;

<R, S> boolean receiveAndReply(String queueName, ReceiveAndReplyCallback<R, S> callback,
			ReplyToAddressCallback<S> replyToAddressCallback) throws AmqpException;

The AmqpTemplate implementation takes care of the receive and reply phases. In most cases you should provide only an implementation of ReceiveAndReplyCallback to perform some business logic for the received message and build a reply object or message, if needed. Note, a ReceiveAndReplyCallback may return null. In this case no reply is sent and receiveAndReply works like the receive method. This allows the same queue to be used for a mixture of messages, some of which may not need a reply.

Automatic message (request and reply) conversion is applied only if the provided callback is not an instance of ReceiveAndReplyMessageCallback - which provides a raw message exchange contract.

The ReplyToAddressCallback is useful for cases requiring custom logic to determine the replyTo address at runtime against the received message and reply from the ReceiveAndReplyCallback. By default, replyTo information in the request message is used to route the reply.

The following is an example of POJO-based receive and reply…​

boolean received =
        this.template.receiveAndReply(ROUTE, new ReceiveAndReplyCallback<Order, Invoice>() {

                public Invoice handle(Order order) {
                        return processOrder(order);
                }
        });
if (received) {
        log.info("We received an order!");
}

Asynchronous Consumer

[Important]Important

Spring AMQP also supports annotated-listener endpoints through the use of the @RabbitListener annotation and provides an open infrastructure to register endpoints programmatically. This is by far the most convenient way to setup an asynchronous consumer, see the section called “Annotation-driven Listener Endpoints” for more details.

[Important]Important

The prefetch default value used to be 1, which could lead to under-utilization of efficient consumers. Starting with version 2.0, the default prefetch value is now 250, which should keep consumers busy in most common scenarios and thus improve throughput.

There are nevertheless scenarios where the prefetch value should be low: for example, with large messages, especially if the processing is slow (messages could add up to a large amount of memory in the client process), and if strict message ordering is necessary (the prefetch value should be set back to 1 in this case).

Also, with low-volume messaging and multiple consumers (including concurrency within a single listener container instance), you may wish to reduce the prefetch to get a more even distribution of messages across consumers. It is also recomended to use prefetch = 1 with the MANUAL ack mode. The basicAck is async operation and if something wrong happens on the Broker (double ack for the same delivery tag, for example), you end up with processed subsequent messages in the batch, but unacked on the Broker and other consumer may see them.

See Section 3.1.15, “Message Listener Container Configuration”.

For more background about prefetch, see this post about consumer utilization in RabbitMQ and this post about queuing theory.

Message Listener

For asynchronous Message reception, a dedicated component (not the AmqpTemplate) is involved. That component is a container for a Message consuming callback. We will look at the container and its properties in just a moment, but first we should look at the callback since that is where your application code will be integrated with the messaging system. There are a few options for the callback starting with an implementation of the MessageListener interface:

public interface MessageListener {
    void onMessage(Message message);
}

If your callback logic depends upon the AMQP Channel instance for any reason, you may instead use the ChannelAwareMessageListener. It looks similar but with an extra parameter:

public interface ChannelAwareMessageListener {
    void onMessage(Message message, Channel channel) throws Exception;
}
MessageListenerAdapter

If you prefer to maintain a stricter separation between your application logic and the messaging API, you can rely upon an adapter implementation that is provided by the framework. This is often referred to as "Message-driven POJO" support.

[Note]Note

Version 1.5 introduced a more flexible mechanism for POJO messaging, the @RabbitListener annotation - see the section called “Annotation-driven Listener Endpoints” for more information.

When using the adapter, you only need to provide a reference to the instance that the adapter itself should invoke.

MessageListenerAdapter listener = new MessageListenerAdapter(somePojo);
listener.setDefaultListenerMethod("myMethod");

You can subclass the adapter and provide an implementation of getListenerMethodName() to dynamically select different methods based on the message. This method has two parameters, the originalMessage and extractedMessage, the latter being the result of any conversion. By default, a SimpleMessageConverter is configured; see the section called “SimpleMessageConverter” for more information and information about other converters available.

Starting with version 1.4.2, the original message has properties consumerQueue and consumerTag which can be used to determine which queue a message was received from.

Starting with version 1.5, you can configure a map of consumer queue/tag to method name, to dynamically select the method to call. If no entry is in the map, we fall back to the default listener method. The default listener method (if not set) is handleMessage.

Starting with version 2.0, a convenient FunctionalInterface has been provided:

@FunctionalInterface
public interface ReplyingMessageListener<T, R> {

	R handleMessage(T t);

}

This facilitates convenient configuration of the adapter using Java 8 lamdas:

new MessageListenerAdapter((ReplyingMessageListener<String, String>) data -> {
    ...
    return result;
}));
Container

Now that you’ve seen the various options for the Message-listening callback, we can turn our attention to the container. Basically, the container handles the "active" responsibilities so that the listener callback can remain passive. The container is an example of a "lifecycle" component. It provides methods for starting and stopping. When configuring the container, you are essentially bridging the gap between an AMQP Queue and the MessageListener instance. You must provide a reference to the ConnectionFactory and the queue name(s) or Queue instance(s) from which that listener should consume Messages.

With versions prior to version 2.0, there was one listener container - the SimpleMessageListenerContainer; there is now a second container - the DirectMessageListenerContainer. The differences between the containers and criteria you might apply when choosing which to use are described in the section called “Choosing a Container”.

Here is the most basic example using the, SimpleMessageListenerContainer :

SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();
container.setConnectionFactory(rabbitConnectionFactory);
container.setQueueNames("some.queue");
container.setMessageListener(new MessageListenerAdapter(somePojo));

As an "active" component, it’s most common to create the listener container with a bean definition so that it can simply run in the background. This can be done via XML:

<rabbit:listener-container connection-factory="rabbitConnectionFactory">
    <rabbit:listener queues="some.queue" ref="somePojo" method="handle"/>
</rabbit:listener-container>

or

<rabbit:listener-container connection-factory="rabbitConnectionFactory" type="direct">
    <rabbit:listener queues="some.queue" ref="somePojo" method="handle"/>
</rabbit:listener-container>

will create a DirectMessageListenerContainer (notice the type attribute - it defaults to simple).

Or, you may prefer to use the @Configuration style which will look very similar to the actual code snippet above:

@Configuration
public class ExampleAmqpConfiguration {

    @Bean
    public SimpleMessageListenerContainer messageListenerContainer() {
        SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();
        container.setConnectionFactory(rabbitConnectionFactory());
        container.setQueueName("some.queue");
        container.setMessageListener(exampleListener());
        return container;
    }

    @Bean
    public ConnectionFactory rabbitConnectionFactory() {
        CachingConnectionFactory connectionFactory =
            new CachingConnectionFactory("localhost");
        connectionFactory.setUsername("guest");
        connectionFactory.setPassword("guest");
        return connectionFactory;
    }

    @Bean
    public MessageListener exampleListener() {
        return new MessageListener() {
            public void onMessage(Message message) {
                System.out.println("received: " + message);
            }
        };
    }
}

Starting with RabbitMQ Version 3.2, the broker now supports consumer priority (see Using Consumer Priorities with RabbitMQ). This is enabled by setting the x-priority argument on the consumer. The SimpleMessageListenerContainer now supports setting consumer arguments:

container.setConsumerArguments(Collections.
<String, Object> singletonMap("x-priority", Integer.valueOf(10)));

For convenience, the namespace provides the priority attribute on the listener element:

<rabbit:listener-container connection-factory="rabbitConnectionFactory">
    <rabbit:listener queues="some.queue" ref="somePojo" method="handle" priority="10" />
</rabbit:listener-container>

Starting with version 1.3 the queue(s) on which the container is listening can be modified at runtime; see Section 3.1.18, “Listener Container Queues”.

auto-delete Queues

When a container is configured to listen to auto-delete queue(s), or the queue has an x-expires option or the Time-To-Live policy is configured on the Broker, the queue is removed by the broker when the container is stopped (last consumer is cancelled). Before version 1.3, the container could not be restarted because the queue was missing; the RabbitAdmin only automatically redeclares queues etc, when the connection is closed/opens, which does not happen when the container is stopped/started.

Starting with version 1.3, the container will now use a RabbitAdmin to redeclare any missing queues during startup.

You can also use conditional declaration (the section called “Conditional Declaration”) together with an auto-startup="false" admin to defer queue declaration until the container is started.

<rabbit:queue id="otherAnon" declared-by="containerAdmin" />

<rabbit:direct-exchange name="otherExchange" auto-delete="true" declared-by="containerAdmin">
    <rabbit:bindings>
        <rabbit:binding queue="otherAnon" key="otherAnon" />
    </rabbit:bindings>
</rabbit:direct-exchange>

<rabbit:listener-container id="container2" auto-startup="false">
    <rabbit:listener id="listener2" ref="foo" queues="otherAnon" admin="containerAdmin" />
</rabbit:listener-container>

<rabbit:admin id="containerAdmin" connection-factory="rabbitConnectionFactory"
    auto-startup="false" />

In this case, the queue and exchange are declared by containerAdmin which has auto-startup="false" so the elements are not declared during context initialization. Also, the container is not started for the same reason. When the container is later started, it uses it’s reference to containerAdmin to declare the elements.

Batched Messages

Batched messages are automatically de-batched by listener containers (using the springBatchFormat message header). Rejecting any message from a batch will cause the entire batch to be rejected. See the section called “Batching” for more information about batching.

Consumer Failure Events

The containers publish application events whenever a listener (consumer) experiences a failure of some kind. The event ListenerContainerConsumerFailedEvent has the following properties:

  • container - the listener container where the consumer experienced the problem.
  • reason - a textual reason for the failure.
  • fatal - a boolean indicating whether the failure was fatal; with non-fatal exceptions, the container will attempt to restart the consumer, according to the recoveryInterval or recoveryBackoff (for the SimpleMessageListenerContainer) or the monitorInterval (for the DirectMessageListenerContainer).
  • throwable - the Throwable that was caught.

These events can be consumed by implementing ApplicationListener<ListenerContainerConsumerFailedEvent>.

[Note]Note

System-wide events (such as connection failures) will be published by all consumers when concurrentConsumers is greater than 1.

If a consumer fails because one if its queues is being used exclusively, by default, as well as publishing the event, a WARN log is issued. To change this logging behavior, provide a custom ConditionalExceptionLogger in the SimpleMessageListenerContainer 's exclusiveConsumerExceptionLogger property. See also the section called “Logging Channel Close Events”.

Fatal errors are always logged at ERROR level; this it not modifiable.

Consumer Tags

You can provide a strategy to generate consumer tags. By default, the consumer tag will be generated by the broker.

public interface ConsumerTagStrategy {

    String createConsumerTag(String queue);

}

The queue is made available so it can (optionally) be used in the tag.

See Section 3.1.15, “Message Listener Container Configuration”.

Annotation-driven Listener Endpoints

Introduction

The easiest way to receive a message asynchronously is to use the annotated listener endpoint infrastructure. In a nutshell, it allows you to expose a method of a managed bean as a Rabbit listener endpoint.

@Component
public class MyService {

    @RabbitListener(queues = "myQueue")
    public void processOrder(String data) {
        ...
    }

}

The idea of the example above is that, whenever a message is available on the queue named myQueue, the processOrder method is invoked accordingly (in this case, with the payload of the message).

The annotated endpoint infrastructure creates a message listener container behind the scenes for each annotated method, using a RabbitListenerContainerFactory.

In the example above, myQueue must already exist and be bound to some exchange. The queue can be declared and bound automatically, as long as a RabbitAdmin exists in the application context.

[Note]Note

Property placeholders (${some.property}) or SpEL expressions (#{someExpression}) can be specified for the annotation properties (queues etc). See the section called “Listening to Multiple Queues” for an example of why you might use SpEL instead of a property placeholder.

@Component
public class MyService {

  @RabbitListener(bindings = @QueueBinding(
        value = @Queue(value = "myQueue", durable = "true"),
        exchange = @Exchange(value = "auto.exch", ignoreDeclarationExceptions = "true"),
        key = "orderRoutingKey")
  )
  public void processOrder(Order order) {
    ...
  }

  @RabbitListener(bindings = @QueueBinding(
        value = @Queue,
        exchange = @Exchange(value = "auto.exch"),
        key = "invoiceRoutingKey")
  )
  public void processInvoice(Invoice invoice) {
    ...
  }

  @RabbitListener(queuesToDeclare = @Queue(name = "${my.queue}", durable = "true"))
  public String handleWithSimpleDeclare(String data) {
      ...
  }

}

In the first example, a queue myQueue will be declared automatically (durable) together with the exchange, if needed, and bound to the exchange with the routing key. In the second example, an anonymous (exclusive, auto-delete) queue will be declared and bound. Multiple QueueBinding entries can be provided, allowing the listener to listen to multiple queues. In the third example, a queue with the name retrieved from property my.queue will be declared if necessary, with the default binding to the default exchange using the queue name as the routing key.

Since version 2.0 the @Exchange annotation supports any exchange types, including custom. See more information in the AMQP Concepts document.

Use normal @Bean definitions when more advanced configuration is required.

Notice ignoreDeclarationExceptions on the exchange in the first example. This allows, for example, binding to an existing exchange that might have different settings (such as internal). By default the properties of an existing exchange must match.

Starting with version 2.0, you can now bind a queue to an exchange with multiple routing keys:

...
    key = { "red", "yellow" }
...

You can also specify arguments within @QueueBinding annotations for queues, exchanges and bindings. For example:

@RabbitListener(bindings = @QueueBinding(
        value = @Queue(value = "auto.headers", autoDelete = "true",
                        arguments = @Argument(name = "x-message-ttl", value = "10000",
                                                type = "java.lang.Integer")),
        exchange = @Exchange(value = "auto.headers", type = ExchangeTypes.HEADERS, autoDelete = "true"),
        arguments = {
                @Argument(name = "x-match", value = "all"),
                @Argument(name = "foo", value = "bar"),
                @Argument(name = "baz")
        })
)
public String handleWithHeadersExchange(String foo) {
    ...
}

Notice that the x-message-ttl argument is set to 10 seconds for the queue. Since the argument type is not String, we have to specify its type; in this case Integer. As with all such declarations, if the queue exists already, the arguments must match those on the queue. For the header exchange, we set the binding arguments to match messages that have the header foo set to bar and the header baz must be present with any value. The x-match argument means both conditions must be satisfied.

The argument name, value, and type can be property placeholders (${...}) or SpEL expressions (#{...}). The name must resolve to a String; the expression for type must resolve to a Class or the fully-qualified name of a class. The value must resolve to something that can be converted by the DefaultConversionService to the type (such as the x-message-ttl in the above example).

If a name resolves to null or an empty String, that @Argument is ignored.

Meta-Annotations

Sometimes you may want to use the same configuration for multiple listeners. To reduce the boilerplate configuration, you can use meta-annotations to create your own listener annotation:

@Target({ElementType.TYPE, ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@RabbitListener(bindings = @QueueBinding(
        value = @Queue,
        exchange = @Exchange(value = "metaFanout", type = ExchangeTypes.FANOUT)))
public @interface MyAnonFanoutListener {
}

public class MetaListener {

    @MyAnonFanoutListener
    public void handle1(String foo) {
        ...
    }

    @MyAnonFanoutListener
    public void handle2(String foo) {
        ...
    }

}

In this example, each listener created by the @MyAnonFanoutListener annotation will bind an anonymous, auto-delete queue to the fanout exchange metaFanout. The meta-annotation mechanism is simple in that attributes on the user-defined annotation are not examined - so you can’t override settings from the meta-annotation. Use normal @Bean definitions when more advanced configuration is required.

Enable Listener Endpoint Annotations

To enable support for @RabbitListener annotations add @EnableRabbit to one of your @Configuration classes.

@Configuration
@EnableRabbit
public class AppConfig {

    @Bean
    public SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory() {
        SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
        factory.setConnectionFactory(connectionFactory());
        factory.setConcurrentConsumers(3);
        factory.setMaxConcurrentConsumers(10);
        return factory;
    }
}

Since version 2.0, a DirectMessageListenerContainerFactory is also available, which creates DirectMessageListenerContainer s.

[Note]Note

To choose between the SimpleRabbitListenerContainerFactory and DirectRabbitListenerContainerFactory see the section called “Choosing a Container”.

By default, the infrastructure looks for a bean named rabbitListenerContainerFactory as the source for the factory to use to create message listener containers. In this case, and ignoring the RabbitMQ infrastructure setup, the processOrder method can be invoked with a core poll size of 3 threads and a maximum pool size of 10 threads.

It is possible to customize the listener container factory to use per annotation or an explicit default can be configured by implementing the RabbitListenerConfigurer interface. The default is only required if at least one endpoint is registered without a specific container factory. See the javadoc for full details and examples.

If you prefer XML configuration, use the <rabbit:annotation-driven> element; any beans annotated with @RabbitListener will be detected.

For SimpleRabbitListenerContainer s:

<rabbit:annotation-driven/>

<bean id="rabbitListenerContainerFactory"
      class="org.springframework.amqp.rabbit.config.SimpleRabbitListenerContainerFactory">
    <property name="connectionFactory" ref="connectionFactory"/>
    <property name="concurrentConsumers" value="3"/>
    <property name="maxConcurrentConsumers" value="10"/>
</bean>

and for DirectMessageListenerContainer s:

<rabbit:annotation-driven/>

<bean id="rabbitListenerContainerFactory"
      class="org.springframework.amqp.rabbit.config.DirectRabbitListenerContainerFactory">
    <property name="connectionFactory" ref="connectionFactory"/>
    <property name="consumersPerQueue" value="3"/>
</bean>

Starting with version 2.0, the @RabbitListener annotation has a concurrency property; it supports SpEL expressions (#{...}) and property placeholders (${...}). Its meaning, and allowed values, depend on the container type.

  • For the DirectMessageListenerContainer, the value must be a single integer value, which sets the consumersPerQueue property on the container.
  • For the SimpleRabbitListenerContainer, the value can be a single integer value, which sets the concurrentConsumers property on the container, or it can have the form m-n where m is the concurrentConsumers property, and n is the maxConcurrentConsumers property.

In either case, this setting overrides the setting(s) on the factory. Previously you had to define different container factories if you had listeners that required different concurrency.

Message Conversion for Annotated Methods

There are two conversion steps in the pipeline before invoking the listener. The first uses a MessageConverter to convert the incoming Spring AMQP Message to a spring-messaging Message. When the target method is invoked, the message payload is converted, if necessary, to the method parameter type.

The default MessageConverter for the first step is a Spring AMQP SimpleMessageConverter that handles conversion to String and java.io.Serializable objects; all others remain as a byte[]. In the following discussion, we call this the message converter.

The default converter for the second step is a GenericMessageConverter which delegates to a conversion service (an instance of DefaultFormattingConversionService). In the following discussion, we call this the method argument converter.

To change the message converter, simply add it as a property to the container factory bean:

@Bean
public SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory() {
    SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
    ...
    factory.setMessageConverter(new Jackson2JsonMessageConverter());
    ...
    return factory;
}

This configures a Jackson2 converter that expects header information to be present to guide the conversion.

You can also consider a ContentTypeDelegatingMessageConverter which can handle conversion of different content types.

In most cases, it is not necessary to customize the method argument converter unless, for example, you want to use a custom ConversionService.

In versions prior to 1.6, the type information to convert the JSON had to be provided in message headers, or a custom ClassMapper was required. Starting with version 1.6, if there are no type information headers, the type can be inferred from the target method arguments.

[Note]Note

This type inference only works for @RabbitListener at the method level.

See the section called “Jackson2JsonMessageConverter” for more information.

If you wish to customize the method argument converter, you can do so as follows:

@Configuration
@EnableRabbit
public class AppConfig implements RabbitListenerConfigurer {

    ...

    @Bean
    public DefaultMessageHandlerMethodFactory myHandlerMethodFactory() {
        DefaultMessageHandlerMethodFactory factory = new DefaultMessageHandlerMethodFactory();
        factory.setMessageConverter(new GenericMessageConverter(myConversionService()));
        return factory;
    }

    @Bean
    public ConversionService myConversionService() {
        DefaultConversionService conv = new DefaultConversionService();
        conv.addConverter(mySpecialConverter());
        return conv;
    }

    @Override
    public void configureRabbitListeners(RabbitListenerEndpointRegistrar registrar) {
        registrar.setMessageHandlerMethodFactory(myHandlerMethodFactory());
    }

    ...

}
[Important]Important

for multi-method listeners (see the section called “Multi-Method Listeners”), the method selection is based on the payload of the message after the message conversion; the method argument converter is only called after the method has been selected.

Programmatic Endpoint Registration

RabbitListenerEndpoint provides a model of a Rabbit endpoint and is responsible for configuring the container for that model. The infrastructure allows you to configure endpoints programmatically in addition to the ones that are detected by the RabbitListener annotation.

@Configuration
@EnableRabbit
public class AppConfig implements RabbitListenerConfigurer {

    @Override
    public void configureRabbitListeners(RabbitListenerEndpointRegistrar registrar) {
        SimpleRabbitListenerEndpoint endpoint = new SimpleRabbitListenerEndpoint();
        endpoint.setQueueNames("anotherQueue");
        endpoint.setMessageListener(message -> {
            // processing
        });
        registrar.registerEndpoint(endpoint);
    }
}

In the example above, we used SimpleRabbitListenerEndpoint which provides the actual MessageListener to invoke but you could just as well build your own endpoint variant describing a custom invocation mechanism.

It should be noted that you could just as well skip the use of @RabbitListener altogether and only register your endpoints programmatically through RabbitListenerConfigurer.

Annotated Endpoint Method Signature

So far, we have been injecting a simple String in our endpoint but it can actually have a very flexible method signature. Let’s rewrite it to inject the Order with a custom header:

@Component
public class MyService {

    @RabbitListener(queues = "myQueue")
    public void processOrder(Order order, @Header("order_type") String orderType) {
        ...
    }
}

These are the main elements you can inject in listener endpoints:

The raw org.springframework.amqp.core.Message.

The com.rabbitmq.client.Channel on which the message was received

The org.springframework.messaging.Message representing the incoming AMQP message. Note that this message holds both the custom and the standard headers (as defined by AmqpHeaders).

[Note]Note

Starting with version 1.6, the inbound deliveryMode header is now available in the header with name AmqpHeaders.RECEIVED_DELIVERY_MODE instead of AmqpHeaders.DELIVERY_MODE.

@Header-annotated method arguments to extract a specific header value, including standard AMQP headers.

@Headers-annotated argument that must also be assignable to java.util.Map for getting access to all headers.

A non-annotated element that is not one of the supported types (i.e. Message and Channel) is considered to be the payload. You can make that explicit by annotating the parameter with @Payload. You can also turn on validation by adding an extra @Valid.

The ability to inject Spring’s Message abstraction is particularly useful to benefit from all the information stored in the transport-specific message without relying on transport-specific API.

@RabbitListener(queues = "myQueue")
public void processOrder(Message<Order> order) { ...
}

Handling of method arguments is provided by DefaultMessageHandlerMethodFactory which can be further customized to support additional method arguments. The conversion and validation support can be customized there as well.

For instance, if we want to make sure our Order is valid before processing it, we can annotate the payload with @Valid and configure the necessary validator as follows:

@Configuration
@EnableRabbit
public class AppConfig implements RabbitListenerConfigurer {

    @Override
    public void configureRabbitListeners(RabbitListenerEndpointRegistrar registrar) {
        registrar.setMessageHandlerMethodFactory(myHandlerMethodFactory());
    }

    @Bean
    public DefaultMessageHandlerMethodFactory myHandlerMethodFactory() {
        DefaultMessageHandlerMethodFactory factory = new DefaultMessageHandlerMethodFactory();
        factory.setValidator(myValidator());
        return factory;
    }
}
Listening to Multiple Queues

When using the queues attribute, you can specify that the associated container can listen to multiple queues. You can use a @Header annotation to make the queue name from which a message was received available to the POJO method:

@Component
public class MyService {

    @RabbitListener(queues = { "queue1", "queue2" } )
    public void processOrder(String data, @Header(AmqpHeaders.CONSUMER_QUEUE) String queue) {
        ...
    }

}

Starting with version 1.5, you can externalize the queue names using property placeholders, and SpEL:

@Component
public class MyService {

    @RabbitListener(queues = "#{'${property.with.comma.delimited.queue.names}'.split(',')}" )
    public void processOrder(String data, @Header(AmqpHeaders.CONSUMER_QUEUE) String queue) {
        ...
    }

}

Prior to version 1.5, only a single queue could be specified this way; each queue needed a separate property.

Reply Management

The existing support in MessageListenerAdapter already allows your method to have a non-void return type. When that’s the case, the result of the invocation is encapsulated in a message sent either in the address specified in the ReplyToAddress header of the original message or in the default address configured on the listener. That default address can now be set using the @SendTo annotation of the messaging abstraction.

Assuming our processOrder method should now return an OrderStatus, it is possible to write it as follow to automatically send a reply:

@RabbitListener(destination = "myQueue")
@SendTo("status")
public OrderStatus processOrder(Order order) {
    // order processing
    return status;
}

If you need to set additional headers in a transport-independent manner, you could return a Message instead, something like:

@RabbitListener(destination = "myQueue")
@SendTo("status")
public Message<OrderStatus> processOrder(Order order) {
    // order processing
    return MessageBuilder
        .withPayload(status)
        .setHeader("code", 1234)
        .build();
}

The @SendTo value is assumed as a reply exchange and routingKey pair following the pattern exchange/routingKey, where one of those parts can be omitted. The valid values are:

foo/bar - the replyTo exchange and routingKey.

foo/ - the replyTo exchange and default (empty) routingKey.

bar or /bar - the replyTo routingKey and default (empty) exchange.

/ or empty - the replyTo default exchange and default routingKey.

Also @SendTo can be used without a value attribute. This case is equal to an empty sendTo pattern. @SendTo is only used if the inbound message does not have a replyToAddress property.

Starting with version 1.5, the @SendTo value can be a bean initialization SpEL Expression, for example…​

@RabbitListener(queues = "test.sendTo.spel")
@SendTo("#{spelReplyTo}")
public String capitalizeWithSendToSpel(String foo) {
    return foo.toUpperCase();
}
...
@Bean
public String spelReplyTo() {
    return "test.sendTo.reply.spel";
}

The expression must evaluate to a String, which can be a simple queue name (sent to the default exchange) or with the form exchange/routingKey as discussed above.

[Note]Note

The #{...} expression is evaluated once, during initialization.

For dynamic reply routing, the message sender should include a reply_to message property or use the alternate runtime SpEL expression described below.

Starting with version 1.6, the @SendTo can be a SpEL expression that is evaluated at runtime against the request and reply:

@RabbitListener(queues = "test.sendTo.spel")
@SendTo("!{'some.reply.queue.with.' + result.queueName}")
public Bar capitalizeWithSendToSpel(Foo foo) {
    return processTheFooAndReturnABar(foo);
}

The runtime nature of the SpEL expression is indicated with !{...} delimiters. The evaluation context #root object for the expression has three properties:

  • request - the o.s.amqp.core.Message request object.
  • source - the o.s.messaging.Message<?> after conversion.
  • result - the method result.

The context has a map property accessor, a standard type converter and a bean resolver, allowing other beans in the context to be referenced (e.g. @someBeanName.determineReplyQ(request, result)).

In summary, #{...} is evaluated once during initialization, with the #root object being the application context; beans are referenced by their names. !{...} is evaluated at runtime for each message with the root object having the properties above and beans are referenced with their names, prefixed by @.

Multi-Method Listeners

Starting with version 1.5.0, the @RabbitListener annotation can now be specified at the class level. Together with the new @RabbitHandler annotation, this allows a single listener to invoke different methods, based on the payload type of the incoming message. This is best described using an example:

@RabbitListener(id="multi", queues = "someQueue")
public class MultiListenerBean {

    @RabbitHandler
    @SendTo("my.reply.queue")
    public String bar(Bar bar) {
        ...
    }

    @RabbitHandler
    public String baz(Baz baz) {
        ...
    }

    @RabbitHandler
    public String qux(@Header("amqp_receivedRoutingKey") String rk, @Payload Qux qux) {
        ...
    }

}

In this case, the individual @RabbitHandler methods are invoked if the converted payload is a Bar, Baz or Qux. It is important to understand that the system must be able to identify a unique method based on the payload type. The type is checked for assignability to a single parameter that has no annotations, or is annotated with the @Payload annotation. Notice that the same method signatures apply as discussed in the method-level @RabbitListener described above.

Notice that the @SendTo must be specified on each method (if needed); it is not supported at the class level.

@Repeatable @RabbitListener

Starting with version 1.6, the @RabbitListener annotation is marked with @Repeatable. This means that the annotation can appear on the same annotated element (method or class) multiple times. In this case, a separate listener container is created for each annotation, each of which invokes the same listener @Bean. Repeatable annotations can be used with Java 8 or above; when using Java 7 or earlier, the same effect can be achieved by using the @RabbitListeners "container" annotation, with an array of @RabbitListener annotations.

Proxy @RabbitListener and Generics

If your service is intended to be proxied (e.g. in case of @Transactional) there are some considerations when the interface has generic parameters. With a generic interface and a particular implementation, e.g.:

interface TxService<P> {

   String handle(P payload, String header);

}

static class TxServiceImpl implements TxService<Foo> {

    @Override
    @RabbitListener(...)
    public String handle(Foo foo, String rk) {
         ...
    }

}

you are forced to switch to the CGLIB target class proxy because the actual implementation of the interface handle method is a bridge method. In the case of transaction management, the use of CGLIB is configured using an annotation option - @EnableTransactionManagement(proxyTargetClass = true). And in this case, all annotations have to be declared on the target method in the implementation:

static class TxServiceImpl implements TxService<Foo> {

    @Override
    @Transactional
    @RabbitListener(...)
    public String handle(@Payload Foo foo, @Header("amqp_receivedRoutingKey") String rk) {
        ...
    }

}
Handling Exceptions

By default, if an annotated listener method throws an exception, it is thrown to the container and the message will be requeued and redelivered, discarded, or routed to a Dead Letter Exchange, depending on the container and broker configuration. Nothing is returned to the sender.

Starting with version 2.0, the @RabbitListener annotation has two new attributes: errorHandler and returnExceptions.

These are not configured by default.

Use the errorHandler to provide the bean name of a RabbitListenerErrorHandler implementation. This functional interface has one method:

@FunctionalInterface
public interface RabbitListenerErrorHandler {

    Object handleError(Message amqpMessage, org.springframework.messaging.Message<?> message,
              ListenerExecutionFailedException exception) throws Exception;

}

As you can see, you have access to the raw message received from the container, the spring-messaging Message<?> object produced by the message converter and the exception that was thrown by the listener, wrapped in a ListenerExecutionFailedException. The error handler can either return some result which will be sent as the reply, or throw the original or a new exception which will be thrown to the container, or returned to the sender, depending on the returnExceptions setting.

The returnExceptions attribute, when "true" will cause exceptions to be returned to the sender. The exception is wrapped in a RemoteInvocationResult object. On the sender side, there is an available RemoteInvocationAwareMessageConverterAdapter which, if configured into the RabbitTemplate, will re-throw the server-side exception, wrapped in an AmqpRemoteException. The stack trace of the server exception will be synthesized by merging the server and client stack traces.

[Important]Important

This mechanism will generally only work with the default SimpleMessageConverter, which uses Java serialization; exceptions are generally not "Jackson-friendly" so can’t be serialized to JSON. If you are using JSON, consider using an errorHandler to return some other Jackson-friendly Error object when an exception is thrown.

Container Management

Containers created for annotations are not registered with the application context. You can obtain a collection of all containers by invoking getListenerContainers() on the RabbitListenerEndpointRegistry bean. You can then iterate over this collection, for example, to stop/start all containers or invoke the Lifecycle methods on the registry itself which will invoke the operations on each container.

You can also get a reference to an individual container using its id, using getListenerContainer(String id); for example registry.getListenerContainer("multi") for the container created by the snippet above.

Starting with version 1.5.2, you can obtain the id s of the registered containers with getListenerContainerIds().

Starting with version 1.5, you can now assign a group to the container on the RabbitListener endpoint. This provides a mechanism to get a reference to a subset of containers; adding a group attribute causes a bean of type Collection<MessageListenerContainer> to be registered with the context with the group name.

Threading and Asynchronous Consumers

A number of different threads are involved with asynchronous consumers.

Threads from the TaskExecutor configured in the SimpleMessageListenerContainer are used to invoke the MessageListener when a new message is delivered by RabbitMQ Client. If not configured, a SimpleAsyncTaskExecutor is used. If a pooled executor is used, ensure the pool size is sufficient to handle the configured concurrency. With the DirectMessageListenerContainer, the MessageListener is invoked directly on a RabbitMQ Client thread. In this case, the taskExecutor is used for the task that monitors the consumers.

[Note]Note

When using the default SimpleAsyncTaskExecutor, for the threads the listener is invoked on, the listener container beanName is used in the threadNamePrefix. This is useful for log analysis; it’s generally recommended to always include the thread name in the logging appender configuration. When a TaskExecutor is specifically provided via the taskExecutor property on the container, it is used as is, without modification. It is recommended that you use a similar technique to name the threads created by a custom TaskExecutor bean definition, to aid with thread identification in log messages.

The Executor configured in the CachingConnectionFactory is passed into the RabbitMQ Client when creating the connection, and its threads are used to deliver new messages to the listener container. At the time of writing, if this is not configured, the client uses an internal thread pool executor with a pool size of 5.

[Important]Important

With the DirectMessageListenerContainer you need to ensure that the connection factory is configured with a task executor that had sufficient threads to support your desired concurrency, across all listener containers that use that factory. At the time of writing, the default pool size is only 5.

The RabbitMQ client uses a ThreadFactory to create threads for low-level I/O (socket) operations. To modify this factory, you need to configure the underlying RabbitMQ ConnectionFactory, as discussed in the section called “Configuring the Underlying Client Connection Factory”.

Choosing a Container

Version 2.0 introduced the DirectMessageListenerContainer (DMLC); previously, only the SimpleMessageListenerContainer (SMLC) was available. The SMLC uses an internal queue and a dedicated thread for each consumer; if a container is configured to listen to multiple queues, the same consumer thread is used to process all the queues. Concurrency is controlled by concurrentConsumers and other properties. As messages arrive from the RabbitMQ client, the client thread hands them off to the consumer thread via the queue. This architecture was required because in early versions of the RabbitMQ client, multiple concurrent deliveries were not possible. Newer versions of the client have a revised threading model and can now support concurrency. This has allowed the introduction of the DMLC where the listener is now invoked directly on the RabbitMQ Client thread. Its architecture is therefore actually "simpler" than the SMLC. However, there are some limitations with this approach and certain features of the SMLC are not available with the DMLC; also concurrency is controlled by consumersPerQueue (and the client library’s thread pool); the concurrentConsumers and associated properties are not available with this container.

The following features are available with the SMLC, but not the DMLC:

  • txSize - with the SMLC, you can set this to control how many messages are delivered in a transaction and/or to reduce the number of acks, but it may cause the number of duplicate deliveries to increase after a failure. (The DMLC does have mesagesPerAck which can be used to reduce the acks, the same as with txSize and the SMLC, but it can’t be used with transactions - each message is delivered and ack’d in a separate transaction).
  • maxConcurrentConsumers and consumer scaling intervals/triggers - there is no auto-scaling in the DMLC; it does, however, allow you to programmatically change the consumersPerQueue property and the consumers will be adjusted accordingly.

However, the DMLC has the following benefits over the SMLC:

  • Adding and removing queues at runtime is more efficient; with the SMLC, the entire consumer thread is restarted (all consumers canceled and re-created); with the DMLC, unaffected consumers are not canceled.
  • The context switch between the RabbitMQ Client thread and the consumer thread is avoided.
  • Threads are shared across consumers rather than having a dedicated thread for each consumer in the SMLC. However, see the IMPORTANT note about the connection factory configuration in the section called “Threading and Asynchronous Consumers”.

See Section 3.1.15, “Message Listener Container Configuration” for information about which configuration properties apply to each container.

Detecting Idle Asynchronous Consumers

While efficient, one problem with asynchronous consumers is detecting when they are idle - users might want to take some action if no messages arrive for some period of time.

Starting with version 1.6, it is now possible to configure the listener container to publish a ListenerContainerIdleEvent when some time passes with no message delivery. While the container is idle, an event will be published every idleEventInterval milliseconds.

To configure this feature, set the idleEventInterval on the container:

xml
<rabbit:listener-container connection-factory="connectionFactory"
        ...
        idle-event-interval="60000"
        ...
        >
    <rabbit:listener id="container1" queue-names="foo" ref="myListener" method="handle" />
</rabbit:listener-container>
Java
@Bean
public SimpleMessageListenerContainer(ConnectionFactory connectionFactory) {
    SimpleMessageListenerContainer container = new SimpleMessageListenerContainer(connectionFactory);
    ...
    container.setIdleEventInterval(60000L);
    ...
    return container;
}
@RabbitListener
@Bean
public SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory() {
    SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
    factory.setConnectionFactory(rabbitConnectionFactory());
    factory.setIdleEventInterval(60000L);
    ...
    return factory;
}

In each of these cases, an event will be published once per minute while the container is idle.

Event Consumption

You can capture these events by implementing ApplicationListener - either a general listener, or one narrowed to only receive this specific event. You can also use @EventListener, introduced in Spring Framework 4.2.

The following example combines the @RabbitListener and @EventListener into a single class. It’s important to understand that the application listener will get events for all containers so you may need to check the listener id if you want to take specific action based on which container is idle. You can also use the @EventListener condition for this purpose.

The events have 4 properties:

  • source - the listener container instance
  • id - the listener id (or container bean name)
  • idleTime - the time the container had been idle when the event was published
  • queueNames - the names of the queue(s) that the container listens to
public class Listener {

    @RabbitListener(id="foo", queues="#{queue.name}")
    public String listen(String foo) {
        return foo.toUpperCase();
    }

    @EventListener(condition = "event.listenerId == 'foo'")
    public void onApplicationEvent(ListenerContainerIdleEvent event) {
        ...
    }

}
[Important]Important

Event listeners will see events for all containers; so, in the example above, we narrow the events received based on the listener ID.

[Caution]Caution

If you wish to use the idle event to stop the lister container, you should not call container.stop() on the thread that calls the listener - it will cause delays and unnecessary log messages. Instead, you should hand off the event to a different thread that can then stop the container.

3.1.7 Message Converters

Introduction

The AmqpTemplate also defines several methods for sending and receiving Messages that will delegate to a MessageConverter. The MessageConverter itself is quite straightforward. It provides a single method for each direction: one for converting to a Message and another for converting from a Message. Notice that when converting to a Message, you may also provide properties in addition to the object. The "object" parameter typically corresponds to the Message body.

public interface MessageConverter {

    Message toMessage(Object object, MessageProperties messageProperties)
            throws MessageConversionException;

    Object fromMessage(Message message) throws MessageConversionException;

}

The relevant Message-sending methods on the AmqpTemplate are listed below. They are simpler than the methods we discussed previously because they do not require the Message instance. Instead, the MessageConverter is responsible for "creating" each Message by converting the provided object to the byte array for the Message body and then adding any provided MessageProperties.

void convertAndSend(Object message) throws AmqpException;

void convertAndSend(String routingKey, Object message) throws AmqpException;

void convertAndSend(String exchange, String routingKey, Object message)
    throws AmqpException;

void convertAndSend(Object message, MessagePostProcessor messagePostProcessor)
    throws AmqpException;

void convertAndSend(String routingKey, Object message,
    MessagePostProcessor messagePostProcessor) throws AmqpException;

void convertAndSend(String exchange, String routingKey, Object message,
    MessagePostProcessor messagePostProcessor) throws AmqpException;

On the receiving side, there are only two methods: one that accepts the queue name and one that relies on the template’s "queue" property having been set.

Object receiveAndConvert() throws AmqpException;

Object receiveAndConvert(String queueName) throws AmqpException;
[Note]Note

The MessageListenerAdapter mentioned in the section called “Asynchronous Consumer” also uses a MessageConverter.

SimpleMessageConverter

The default implementation of the MessageConverter strategy is called SimpleMessageConverter. This is the converter that will be used by an instance of RabbitTemplate if you do not explicitly configure an alternative. It handles text-based content, serialized Java objects, and simple byte arrays.

Converting From a Message

If the content type of the input Message begins with "text" (e.g. "text/plain"), it will also check for the content-encoding property to determine the charset to be used when converting the Message body byte array to a Java String. If no content-encoding property had been set on the input Message, it will use the "UTF-8" charset by default. If you need to override that default setting, you can configure an instance of SimpleMessageConverter, set its "defaultCharset" property and then inject that into a RabbitTemplate instance.

If the content-type property value of the input Message is set to "application/x-java-serialized-object", the SimpleMessageConverter will attempt to deserialize (rehydrate) the byte array into a Java object. While that might be useful for simple prototyping, it’s generally not recommended to rely on Java serialization since it leads to tight coupling between the producer and consumer. Of course, it also rules out usage of non-Java systems on either side. With AMQP being a wire-level protocol, it would be unfortunate to lose much of that advantage with such restrictions. In the next two sections, we’ll explore some alternatives for passing rich domain object content without relying on Java serialization.

For all other content-types, the SimpleMessageConverter will return the Message body content directly as a byte array.

See the section called “Java Deserialization” for important information.

Converting To a Message

When converting to a Message from an arbitrary Java Object, the SimpleMessageConverter likewise deals with byte arrays, Strings, and Serializable instances. It will convert each of these to bytes (in the case of byte arrays, there is nothing to convert), and it will set the content-type property accordingly. If the Object to be converted does not match one of those types, the Message body will be null.

SerializerMessageConverter

This converter is similar to the SimpleMessageConverter except it can be configured with other Spring Framework Serializer and Deserializer implementations for application/x-java-serialized-object conversions.

See the section called “Java Deserialization” for important information.

Jackson2JsonMessageConverter

Converting to a Message

As mentioned in the previous section, relying on Java serialization is generally not recommended. One rather common alternative that is more flexible and portable across different languages and platforms is JSON (JavaScript Object Notation). The converter can be configured on any RabbitTemplate instance to override its usage of the SimpleMessageConverter default. The Jackson2JsonMessageConverter uses the com.fasterxml.jackson 2.x library.

<bean class="org.springframework.amqp.rabbit.core.RabbitTemplate">
    <property name="connectionFactory" ref="rabbitConnectionFactory"/>
    <property name="messageConverter">
        <bean class="org.springframework.amqp.support.converter.Jackson2JsonMessageConverter">
            <!-- if necessary, override the DefaultClassMapper -->
            <property name="classMapper" ref="customClassMapper"/>
        </bean>
    </property>
</bean>

As shown above, Jackson2JsonMessageConverter uses a DefaultClassMapper by default. Type information is added to (and retrieved from) the MessageProperties. If an inbound message does not contain type information in the MessageProperties, but you know the expected type, you can configure a static type using the defaultType property

<bean id="jsonConverterWithDefaultType"
      class="o.s.amqp.support.converter.Jackson2JsonMessageConverter">
    <property name="classMapper">
        <bean class="org.springframework.amqp.support.converter.DefaultClassMapper">
            <property name="defaultType" value="foo.PurchaseOrder"/>
        </bean>
    </property>
</bean>

In addition, you can provide custom mappings from the value in the __TypeId__ header…​

@Bean
public Jackson2JsonMessageConverter jsonMessageConverter() {
    Jackson2JsonMessageConverter jsonConverter = new Jackson2JsonMessageConverter();
    jsonConverter.setClassMapper(classMapper());
    return jsonConverter;
}

@Bean
public DefaultClassMapper classMapper() {
    DefaultClassMapper classMapper = new DefaultClassMapper();
    Map<String, Class<?>> idClassMapping = new HashMap<>();
    idClassMapping.put("foo", Foo.class);
    idClassMapping.put("bar", Bar.class);
    classMapper.setIdClassMapping(idClassMapping);
    return classMapper;
}

Now, if the sending system sets the header to foo, the converter will create a Foo object, etc. See the Section 3.3.4, “Receiving JSON from Non-Spring Applications” sample application for a complete discussion about converting messages from non-Spring applications.

Converting from a Message

Inbound messages are converted to objects according to the type information added to headers by the sending system.

In versions prior to 1.6, if type information is not present, conversion would fail. Starting with version 1.6, if type information is missing, the converter will convert the JSON using Jackson defaults (usually a map).

Also, starting with version 1.6, when using @RabbitListener annotations (on methods), the inferred type information is added to the MessageProperties; this allows the converter to convert to the argument type of the target method. This only applies if there is one parameter with no annotations or a single parameter with the @Payload annotation. Parameters of type Message are ignored during the analysis.

[Important]Important

By default, the inferred type information will override the inbound __TypeId__ and related headers created by the sending system. This allows the receiving system to automatically convert to a different domain object. This applies only if the parameter type is concrete (not abstract or an interface) or it is from the java.util package. In all other cases, the __TypeId__ and related headers will be used. There are cases where you might wish to override the default behavior and always use the __TypeId__ information. For example, let’s say you have a @RabbitListener that takes a Foo argument but the message contains a Bar which is a subclass of Foo (which is concrete). The inferred type would be incorrect. To handle this situation, set the TypePrecedence property on the Jackson2JsonMessageConverter to TYPE_ID instead of the default INFERRED. The property is actually on the converter’s DefaultJackson2JavaTypeMapper but a setter is provided on the converter for convenience. If you inject a custom type mapper, you should set the property on the mapper instead.

[Note]Note

When converting from the Message, an incoming MessageProperties.getContentType() must be JSON-compliant (the logic contentType.contains("json") is used). Otherwise, a WARN log message Could not convert incoming message with content-type [...], is emitted and message.getBody() is returned as is - as a byte[]. So, to meet the Jackson2JsonMessageConverter requirements on the consumer side, the producer must add the contentType message property, e.g. as application/json, text/x-json or simply use the Jackson2JsonMessageConverter, which will set the header automatically.

@RabbitListener
public void foo(Foo foo) {...}

@RabbitListener
public void foo(@Payload Foo foo, @Header("amqp_consumerQueue") String queue) {...}

@RabbitListener
public void foo(Foo foo, o.s.amqp.core.Message message) {...}

@RabbitListener
public void foo(Foo foo, o.s.messaging.Message<Foo> message) {...}

@RabbitListener
public void foo(Foo foo, String bar) {...}

@RabbitListener
public void foo(Foo foo, o.s.messaging.Message<?> message) {...}

In the first four cases above the converter will attempt to convert to the Foo type. The fifth example is invalid because we can’t determine which argument should receive the message payload. With the sixth example, the Jackson defaults will apply due to the generic type being a WildcardType.

You can, however, create a custom converter and use the targetMethod message property to decide which type to convert the JSON to.

[Note]Note

This type inference can only be achieved when the @RabbitListener annotation is declared at the method level. With class-level @RabbitListener, the converted type is used to select which @RabbitHandler method to invoke. For this reason, the infrastructure provides the targetObject message property which can be used by a custom converter to determine the type.

[Important]Important

Starting with version 1.6.11, the Jackson2JsonMessageConverter and, therefore, DefaultJackson2JavaTypeMapper (DefaultClassMapper) provide the trustedPackages option to overcome Serialization Gadgets vulnerability. By default, for backward compatiblity the Jackson2JsonMessageConverter trusts all packages - use * for the option.

Converting From a Message With RabbitTemplate

As mentioned above, type information is conveyed in message headers to assist the converter when converting from a message. This works fine in most cases, but when using generic types, it can only convert simple objects and known "container" objects (lists, arrays, maps). Starting with version 2.0, the Jackson2JsonMessageConverter implements SmartMessageConverter which allows it to be used with the new RabbitTemplate methods that take a ParameterizedTypeReference argument; this allows conversion of complex generic types. For example:

Foo<Bar<Baz, Qux>> foo =
    rabbitTemplate.receiveAndConvert(new ParameterizedTypeReference<Foo<Bar<Baz, Qux>>>() { });

MarshallingMessageConverter

Yet another option is the MarshallingMessageConverter. It delegates to the Spring OXM library’s implementations of the Marshaller and Unmarshaller strategy interfaces. You can read more about that library here. In terms of configuration, it’s most common to provide the constructor argument only since most implementations of Marshaller will also implement Unmarshaller.

<bean class="org.springframework.amqp.rabbit.core.RabbitTemplate">
    <property name="connectionFactory" ref="rabbitConnectionFactory"/>
    <property name="messageConverter">
        <bean class="org.springframework.amqp.support.converter.MarshallingMessageConverter">
            <constructor-arg ref="someImplemenationOfMarshallerAndUnmarshaller"/>
        </bean>
    </property>
</bean>

ContentTypeDelegatingMessageConverter

This class was introduced in version 1.4.2 and allows delegation to a specific MessageConverter based on the content type property in the MessageProperties. By default, it will delegate to a SimpleMessageConverter if there is no contentType property, or a value that matches none of the configured converters.

<bean id="contentTypeConverter" class="ContentTypeDelegatingMessageConverter">
    <property name="delegates">
        <map>
            <entry key="application/json" value-ref="jsonMessageConverter" />
            <entry key="application/xml" value-ref="xmlMessageConverter" />
        </map>
    </property>
</bean>

Java Deserialization

[Important]Important

There is a possible vulnerability when deserializing java objects from untrusted sources.

If you accept messages from untrusted sources with a content-type application/x-java-serialized-object, you should consider configuring which packages/classes are allowed to be deserialized. This applies to both the SimpleMessageConverter and SerializerMessageConverter when it is configured to use a DefaultDeserializer - either implicitly, or via configuration.

By default, the white list is empty, meaning all classes will be deserialized.

You can set a list of patterns, such as foo.*, foo.bar.Baz or *.MySafeClass.

The patterns will be checked in order until a match is found. If there is no match, a SecurityException is thrown.

Set the patterns using the whiteListPatterns property on these converters.

Message Properties Converters

The MessagePropertiesConverter strategy interface is used to convert between the Rabbit Client BasicProperties and Spring AMQP MessageProperties. The default implementation (DefaultMessagePropertiesConverter) is usually sufficient for most purposes but you can implement your own if needed. The default properties converter will convert BasicProperties elements of type LongString to String s when the size is not greater than 1024 bytes. Larger LongString s are not converted (see below). This limit can be overridden with a constructor argument.

Starting with version 1.6, headers longer than the long string limit (default 1024) are now left as LongString s by default by the DefaultMessagePropertiesConverter. You can access the contents via the getBytes[], toString(), or getStream() methods.

Previously, the DefaultMessagePropertiesConverter "converted" such headers to a DataInputStream (actually it just referenced the LongString's DataInputStream). On output, this header was not converted (except to a String, e.g. [email protected] by calling toString() on the stream).

Large incoming LongString headers are now correctly "converted" on output too (by default).

A new constructor is provided to allow you to configure the converter to work as before:

/**
 * Construct an instance where LongStrings will be returned
 * unconverted or as a java.io.DataInputStream when longer than this limit.
 * Use this constructor with 'true' to restore pre-1.6 behavior.
 * @param longStringLimit the limit.
 * @param convertLongLongStrings LongString when false,
 * DataInputStream when true.
 * @since 1.6
 */
public DefaultMessagePropertiesConverter(int longStringLimit, boolean convertLongLongStrings) { ... }

Also starting with version 1.6, a new property correlationIdString has been added to MessageProperties. Previously, when converting to/from BasicProperties used by the RabbitMQ client, an unnecessary byte[] <-> String conversion was performed because MessageProperties.correlationId is a byte[] but BasicProperties uses a String. (Ultimately, the RabbitMQ client uses UTF-8 to convert the String to bytes to put in the protocol message).

To provide maximum backwards compatibility, a new property correlationIdPolicy has been added to the DefaultMessagePropertiesConverter. This takes an DefaultMessagePropertiesConverter.CorrelationIdPolicy enum argument. By default it is set to BYTES which replicates the previous behavior.

For inbound messages:

  • STRING - just the correlationIdString property is mapped
  • BYTES - just the correlationId property is mapped
  • BOTH - both properties are mapped

For outbound messages:

  • STRING - just the correlationIdString property is mapped
  • BYTES - just the correlationId property is mapped
  • BOTH - Both properties will be considered, with the String property taking precedence

Also starting with version 1.6, the inbound deliveryMode property is no longer mapped to MessageProperties.deliveryMode, it is mapped to MessageProperties.receivedDeliveryMode instead. Also, the inbound userId property is no longer mapped to MessageProperties.userId, it is mapped to MessageProperties.receivedUserId instead. These changes are to avoid unexpected propagation of these properties if the same MessageProperties object is used for an outbound message.

3.1.8 Modifying Messages - Compression and More

A number of extension points exist where you can perform some processing on a message, either before it is sent to RabbitMQ, or immediately after it is received.

As can be seen in Section 3.1.7, “Message Converters”, one such extension point is in the AmqpTemplate convertAndReceive operations, where you can provide a MessagePostProcessor. For example, after your POJO has been converted, the MessagePostProcessor enables you to set custom headers or properties on the Message.

Starting with version 1.4.2, additional extension points have been added to the RabbitTemplate - setBeforePublishPostProcessors() and setAfterReceivePostProcessors(). The first enables a post processor to run immediately before sending to RabbitMQ. When using batching (see the section called “Batching”), this is invoked after the batch is assembled and before the batch is sent. The second is invoked immediately after a message is received.

These extension points are used for such features as compression and, for this purpose, several MessagePostProcessor s are provided:

  • GZipPostProcessor
  • ZipPostProcessor

for compressing messages before sending, and

  • GUnzipPostProcessor
  • UnzipPostProcessor

for decompressing received messages.

Similarly, the SimpleMessageListenerContainer also has a setAfterReceivePostProcessors() method, allowing the decompression to be performed after messages are received by the container.

3.1.9 Request/Reply Messaging

Introduction

The AmqpTemplate also provides a variety of sendAndReceive methods that accept the same argument options that you have seen above for the one-way send operations (exchange, routingKey, and Message). Those methods are quite useful for request/reply scenarios since they handle the configuration of the necessary "reply-to" property before sending and can listen for the reply message on an exclusive Queue that is created internally for that purpose.

Similar request/reply methods are also available where the MessageConverter is applied to both the request and reply. Those methods are named convertSendAndReceive. See the Javadoc of AmqpTemplate for more detail.

Starting with version 1.5.0, each of the sendAndReceive method variants has an overloaded version that takes CorrelationData. Together with a properly configured connection factory, this enables the receipt of publisher confirms for the send side of the operation. See the section called “Publisher Confirms and Returns” and the javadoc for RabbitOperations for more information.

Starting with version 2.0, there are variants of these methods (convertSendAndReceiveAsType) that take an additional ParameterizedTypeReference argument to convert complex returned types. The template must be configured with a SmartMessageConverter; see the section called “Converting From a Message With RabbitTemplate” for more information.

Reply Timeout

By default, the send and receive methods will timeout after 5 seconds and return null. This can be modified by setting the replyTimeout property. Starting with version 1.5, if you set the mandatory property to true (or the mandatory-expression evaluates to true for a particular message), if the message cannot be delivered to a queue an AmqpMessageReturnedException will be thrown. This exception has returnedMessage, replyCode, replyText properties, as well as the exchange and routingKey used for the send.

[Note]Note

This feature uses publisher returns and is enabled by setting publisherReturns to true on the CachingConnectionFactory (see the section called “Publisher Confirms and Returns”). Also, you must not have registered your own ReturnCallback with the RabbitTemplate.

RabbitMQ Direct reply-to

[Important]Important

Starting with version 3.4.0, the RabbitMQ server now supports Direct reply-to; this eliminates the main reason for a fixed reply queue (to avoid the need to create a temporary queue for each request). Starting with Spring AMQP version 1.4.1 Direct reply-to will be used by default (if supported by the server) instead of creating temporary reply queues. When no replyQueue is provided (or it is set with the name amq.rabbitmq.reply-to), the RabbitTemplate will automatically detect whether Direct reply-to is supported and either use it or fall back to using a temporary reply queue. When using Direct reply-to, a reply-listener is not required and should not be configured.

Reply listeners are still supported with named queues (other than amq.rabbitmq.reply-to), allowing control of reply concurrency etc.

Starting with version 1.6 if, for some reason, you wish to use a temporary, exclusive, auto-delete queue for each reply, set the useTemporaryReplyQueues property to true. This property is ignored if you you set a replyAddress.

The decision whether or not to use direct reply-to can be changed to use different criteria by subclassing RabbitTemplate and overriding useDirectReplyTo(). The method is called once only; when the first request is sent.

With versions earlier than verion 2.0, the RabbitTemplate created a new consumer for each request and canceled the consumer when the reply was received (or timed out). Now, the template uses a DirectReplyToMessageListenerContainer instead, allowing the consumers to be reused; the template still takes care of correlating the replies so there is no danger of a late reply going to a different sender. If you want to revert to the previous behavior, set property useDirectReplyToContainer (direct-reply-to-container when using XML configuration) to false.

The AsynRabbitTemplate has no such option - it always used a DirectReplyToContainer for replies when direct replyTo is being used.

Message Correlation With A Reply Queue

When using a fixed reply queue (other than amq.rabbitmq.reply-to), it is necessary to provide correlation data so that replies can be correlated to requests. See RabbitMQ Remote Procedure Call (RPC). By default, the standard correlationId property will be used to hold the correlation data. However, if you wish to use a custom property to hold correlation data, you can set the correlation-key attribute on the <rabbit-template/>. Explicitly setting the attribute to correlationId is the same as omitting the attribute. Of course, the client and server must use the same header for correlation data.

[Note]Note

Spring AMQP version 1.1 used a custom property spring_reply_correlation for this data. If you wish to revert to this behavior with the current version, perhaps to maintain compatibility with another application using 1.1, you must set the attribute to spring_reply_correlation.

Reply Listener Container

When using RabbitMQ versions prior to 3.4.0, a new temporary queue is used for each reply. However, a single reply queue can be configured on the template, which can be more efficient, and also allows you to set arguments on that queue. In this case, however, you must also provide a <reply-listener/> sub element. This element provides a listener container for the reply queue, with the template being the listener. All of the Section 3.1.15, “Message Listener Container Configuration” attributes allowed on a <listener-container/> are allowed on the element, except for connection-factory and message-converter, which are inherited from the template’s configuration.

[Important]Important

If you run multiple instances of your application or use multiple RabbitTemplate s, you MUST use a unique reply queue for each - RabbitMQ has no capability to select messages from a queue so, if they all use the same queue, each instance would compete for replies and not necessarily receive their own.

<rabbit:template id="amqpTemplate"
        connection-factory="connectionFactory"
        reply-queue="replies"
        reply-address="replyEx/routeReply">
    <rabbit:reply-listener/>
</rabbit:template>

While the container and template share a connection factory, they do not share a channel and therefore requests and replies are not performed within the same transaction (if transactional).

[Note]Note

Prior to version 1.5.0, the reply-address attribute was not available, replies were always routed using the default exchange and the reply-queue name as the routing key. This is still the default but you can now specify the new reply-address attribute. The reply-address can contain an address with the form <exchange>/<routingKey> and the reply will be routed to the specified exchange and routed to a queue bound with the routing key. The reply-address has precedence over reply-queue. The <reply-listener> must be configured as a separate <listener-container> component, when only reply-address is in use, anyway reply-address and reply-queue (or queues attribute on the <listener-container>) must refer to the same queue logically.

With this configuration, a SimpleListenerContainer is used to receive the replies; with the RabbitTemplate being the MessageListener. When defining a template with the <rabbit:template/> namespace element, as shown above, the parser defines the container and wires in the template as the listener.

[Note]Note

When the template does not use a fixed replyQueue (or is using Direct reply-to - see the section called “RabbitMQ Direct reply-to”) a listener container is not needed. Direct reply-to is the preferred mechanism when using RabbitMQ 3.4.0 or later.

If you define your RabbitTemplate as a <bean/>, or using an @Configuration class to define it as an @Bean, or when creating the template programmatically, you will need to define and wire up the reply listener container yourself. If you fail to do this, the template will never receive the replies and will eventually time out and return null as the reply to a call to a sendAndReceive method.

Starting with version 1.5, the RabbitTemplate will detect if it has been configured as a MessageListener to receive replies. If not, attempts to send and receive messages with a reply address will fail with an IllegalStateException (because the replies will never be received).

Further, if a simple replyAddress (queue name) is used, the reply listener container will verify that it is listening to a queue with the same name. This check cannot be performed if the reply address is an exchange and routing key and a debug log message will be written.

[Important]Important

When wiring the reply listener and template yourself, it is important to ensure that the template’s replyQueue and the container’s queues (or queueNames) properties refer to the same queue. The template inserts the reply queue into the outbound message replyTo property.

The following are examples of how to manually wire up the beans.

<bean id="amqpTemplate" class="org.springframework.amqp.rabbit.core.RabbitTemplate">
    <constructor-arg ref="connectionFactory" />
    <property name="exchange" value="foo.exchange" />
    <property name="routingKey" value="foo" />
    <property name="replyQueue" ref="replyQ" />
    <property name="replyTimeout" value="600000" />
</bean>

<bean class="org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer">
    <constructor-arg ref="connectionFactory" />
    <property name="queues" ref="replyQ" />
    <property name="messageListener" ref="amqpTemplate" />
</bean>

<rabbit:queue id="replyQ" name="my.reply.queue" />
    @Bean
    public RabbitTemplate amqpTemplate() {
        RabbitTemplate rabbitTemplate = new RabbitTemplate(connectionFactory());
        rabbitTemplate.setMessageConverter(msgConv());
        rabbitTemplate.setReplyQueue(replyQueue());
        rabbitTemplate.setReplyTimeout(60000);
        return rabbitTemplate;
    }

    @Bean
    public SimpleMessageListenerContainer replyListenerContainer() {
        SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();
        container.setConnectionFactory(connectionFactory());
        container.setQueues(replyQueue());
        container.setMessageListener(amqpTemplate());
        return container;
    }

    @Bean
    public Queue replyQueue() {
        return new Queue("my.reply.queue");
    }

A complete example of a RabbitTemplate wired with a fixed reply queue, together with a "remote" listener container that handles the request and returns the reply is shown in this test case.

[Important]Important

When the reply times out (replyTimeout), the sendAndReceive() methods return null.

Prior to version 1.3.6, late replies for timed out messages were simply logged. Now, if a late reply is received, it is rejected (the template throws an AmqpRejectAndDontRequeueException). If the reply queue is configured to send rejected messages to a dead letter exchange, the reply can be retrieved for later analysis. Simply bind a queue to the configured dead letter exchange with a routing key equal to the reply queue’s name.

Refer to the RabbitMQ Dead Letter Documentation for more information about configuring dead lettering. You can also take a look at the FixedReplyQueueDeadLetterTests test case for an example.

AsyncRabbitTemplate

Version 1.6 introduced the AsyncRabbitTemplate. This has similar sendAndReceive (and convertSendAndReceive) methods to those on the AmqpTemplate but instead of blocking, they return a ListenableFuture.

The sendAndReceive methods return a RabbitMessageFuture; the convertSendAndReceive methods return a RabbitConverterFuture.

You can either synchronously retrieve the result later, by invoking get() on the future, or you can register a callback which will be called asynchronously with the result.

@Autowired
private AsyncRabbitTemplate template;

...

public void doSomeWorkAndGetResultLater() {

    ...

    ListenableFuture<String> future = this.template.convertSendAndReceive("foo");

    // do some more work

    String reply = null;
    try {
        reply = future.get();
    }
    catch (ExecutionException e) {
        ...
    }

    ...

}

public void doSomeWorkAndGetResultAsync() {

    ...

    RabbitConverterFuture<String> future = this.template.convertSendAndReceive("foo");
    future.addCallback(new ListenableFutureCallback<String>() {

        @Override
        public void onSuccess(String result) {
            ...
        }

        @Override
        public void onFailure(Throwable ex) {
            ...
        }

    });

    ...

}

If mandatory is set, and the message can’t be delivered, the future will throw an ExecutionException with a cause of AmqpMessageReturnedException which encapsulates the returned message and information about the return.

If enableConfirms is set, the future will have a property confirm which is itself a ListenableFuture<Boolean> with true indicating a successful publish. If the confirm future is false, the RabbitFuture will have a further property nackCause - the reason for the failure, if available.

[Important]Important

The publisher confirm is discarded if it is received after the reply - since the reply implies a successful publish.

Set the receiveTimeout property on the template to time out replies (it defaults to 30000 - 30 seconds). If a timeout occurs, the future will be completed with an AmqpReplyTimeoutException.

The template implements SmartLifecycle; stopping the template while there are pending replies will cause the pending Future s to be canceled.

Starting with version 2.0, the async template now supports Direct reply-to instead of a configured reply queue. To enable this feature, use one of the following constructors:

public AsyncRabbitTemplate(ConnectionFactory connectionFactory, String exchange, String routingKey)

public AsyncRabbitTemplate(RabbitTemplate template)

See the section called “RabbitMQ Direct reply-to” to use Direct reply-to with the synchronous RabbitTemplate.

Starting with version 2.0, there are variants of these methods (convertSendAndReceiveAsType) that take an additional ParameterizedTypeReference argument to convert complex returned types. The underlying RabbitTemplate must be configured with a SmartMessageConverter; see the section called “Converting From a Message With RabbitTemplate” for more information.

Spring Remoting with AMQP

The Spring Framework has a general remoting capability, allowing Remote Procedure Calls (RPC) using various transports. Spring-AMQP supports a similar mechanism with a AmqpProxyFactoryBean on the client and a AmqpInvokerServiceExporter on the server. This provides RPC over AMQP. On the client side, a RabbitTemplate is used as described above; on the server side, the invoker (configured as a MessageListener) receives the message, invokes the configured service, and returns the reply using the inbound message’s replyTo information.

The client factory bean can be injected into any bean (using its serviceInterface); the client can then invoke methods on the proxy, resulting in remote execution over AMQP.

[Note]Note

With the default MessageConverter s, the method parameters and returned value must be instances of Serializable.

On the server side, the AmqpInvokerServiceExporter has both AmqpTemplate and MessageConverter properties. Currently, the template’s MessageConverter is not used. If you need to supply a custom message converter, then you should provide it using the messageConverter property. On the client side, a custom message converter can be added to the AmqpTemplate which is provided to the AmqpProxyFactoryBean using its amqpTemplate property.

Sample client and server configurations are shown below.

<bean id="client"
	class="org.springframework.amqp.remoting.client.AmqpProxyFactoryBean">
	<property name="amqpTemplate" ref="template" />
	<property name="serviceInterface" value="foo.ServiceInterface" />
</bean>

<rabbit:connection-factory id="connectionFactory" />

<rabbit:template id="template" connection-factory="connectionFactory" reply-timeout="2000"
	routing-key="remoting.binding" exchange="remoting.exchange" />

<rabbit:admin connection-factory="connectionFactory" />

<rabbit:queue name="remoting.queue" />

<rabbit:direct-exchange name="remoting.exchange">
	<rabbit:bindings>
		<rabbit:binding queue="remoting.queue" key="remoting.binding" />
	</rabbit:bindings>
</rabbit:direct-exchange>
<bean id="listener"
	class="org.springframework.amqp.remoting.service.AmqpInvokerServiceExporter">
	<property name="serviceInterface" value="foo.ServiceInterface" />
	<property name="service" ref="service" />
	<property name="amqpTemplate" ref="template" />
</bean>

<bean id="service" class="foo.ServiceImpl" />

<rabbit:connection-factory id="connectionFactory" />

<rabbit:template id="template" connection-factory="connectionFactory" />

<rabbit:queue name="remoting.queue" />

<rabbit:listener-container connection-factory="connectionFactory">
	<rabbit:listener ref="listener" queue-names="remoting.queue" />
</rabbit:listener-container>
[Important]Important

The AmqpInvokerServiceExporter can only process properly formed messages, such as those sent from the AmqpProxyFactoryBean. If it receives a message that it cannot interpret, a serialized RuntimeException will be sent as a reply. If the message has no replyToAddress property, the message will be rejected and permanently lost if no Dead Letter Exchange has been configured.

[Note]Note

By default, if the request message cannot be delivered, the calling thread will eventually timeout and a RemoteProxyFailureException will be thrown. The timeout is 5 seconds by default, and can be modified by setting the replyTimeout property on the RabbitTemplate. Starting with version 1.5, setting the mandatory property to true, and enabling returns on the connection factory (see the section called “Publisher Confirms and Returns”), the calling thread will throw an AmqpMessageReturnedException. See the section called “Reply Timeout” for more information.

3.1.10 Configuring the broker

Introduction

The AMQP specification describes how the protocol can be used to configure Queues, Exchanges and Bindings on the broker. These operations which are portable from the 0.8 specification and higher are present in the AmqpAdmin interface in the org.springframework.amqp.core package. The RabbitMQ implementation of that class is RabbitAdmin located in the org.springframework.amqp.rabbit.core package.

The AmqpAdmin interface is based on using the Spring AMQP domain abstractions and is shown below:

public interface AmqpAdmin {

    // Exchange Operations

    void declareExchange(Exchange exchange);

    void deleteExchange(String exchangeName);

    // Queue Operations

    Queue declareQueue();

    String declareQueue(Queue queue);

    void deleteQueue(String queueName);

    void deleteQueue(String queueName, boolean unused, boolean empty);

    void purgeQueue(String queueName, boolean noWait);

    // Binding Operations

    void declareBinding(Binding binding);

    void removeBinding(Binding binding);

    Properties getQueueProperties(String queueName);

}

Also see the section called “Scoped Operations”.

The getQueueProperties() method returns some limited information about the queue (message count and consumer count). The keys for the properties returned are available as constants in the RabbitTemplate (QUEUE_NAME, QUEUE_MESSAGE_COUNT, QUEUE_CONSUMER_COUNT). The RabbitMQ REST API provides much more information in the QueueInfo object.

The no-arg declareQueue() method defines a queue on the broker with a name that is automatically generated. The additional properties of this auto-generated queue are exclusive=true, autoDelete=true, and durable=false.

The declareQueue(Queue queue) method takes a Queue object and returns the name of the declared queue. If the provided Queue's name property is an empty String, the broker declares the queue with a generated name and that name is returned to the caller. The Queue object itself is not changed. This functionality can only be used programmatically by invoking the RabbitAdmin directly. It is not supported for auto-declaration by the admin by defining a queue declaratively in the application context.

This is in contrast to an AnonymousQueue where the framework generates a unique (UUID) name and sets durable to false and exclusive, autoDelete to true. A <rabbit:queue/> with an empty, or missing, name attribute will always create an AnonymousQueue.

See the section called “AnonymousQueue” to understand why AnonymousQueue is preferred over broker-generated queue names, as well as how to control the format of the name. Declarative queues must have fixed names because they might be referenced elsewhere in the context, for example, in a listener:

<rabbit:listener-container>
    <rabbit:listener ref="listener" queue-names="#{someQueue.name}" />
</rabbit:listener-container>

See the section called “Automatic Declaration of Exchanges, Queues and Bindings”.

The RabbitMQ implementation of this interface is RabbitAdmin which when configured using Spring XML would look like this:

<rabbit:connection-factory id="connectionFactory"/>

<rabbit:admin id="amqpAdmin" connection-factory="connectionFactory"/>

When the CachingConnectionFactory cache mode is CHANNEL (the default), the RabbitAdmin implementation does automatic lazy declaration of Queues, Exchanges and Bindings declared in the same ApplicationContext. These components will be declared as s0on as a Connection is opened to the broker. There are some namespace features that make this very convenient, e.g. in the Stocks sample application we have:

<rabbit:queue id="tradeQueue"/>

<rabbit:queue id="marketDataQueue"/>

<fanout-exchange name="broadcast.responses"
                 xmlns="http://www.springframework.org/schema/rabbit">
    <bindings>
        <binding queue="tradeQueue"/>
    </bindings>
</fanout-exchange>

<topic-exchange name="app.stock.marketdata"
                xmlns="http://www.springframework.org/schema/rabbit">
    <bindings>
        <binding queue="marketDataQueue" pattern="${stocks.quote.pattern}"/>
    </bindings>
</topic-exchange>

In the example above we are using anonymous Queues (actually internally just Queues with names generated by the framework, not by the broker) and refer to them by ID. We can also declare Queues with explicit names, which also serve as identifiers for their bean definitions in the context. E.g.

<rabbit:queue name="stocks.trade.queue"/>
[Tip]Tip

You can provide both an id and a name attribute. This allows you to refer to the queue (for example in a binding) by an id that is independent of the queue name. It also allows standard Spring features such as property placeholders, and SpEL expressions for the queue name; these features are not available when using the name as the bean identifier.

Queues can be configured with additional arguments, for example, x-message-ttl or x-ha-policy. Using the namespace support, they are provided in the form of a Map of argument name/argument value pairs, using the <rabbit:queue-arguments> element.

<rabbit:queue name="withArguments">
    <rabbit:queue-arguments>
        <entry key="x-ha-policy" value="all"/>
    </rabbit:queue-arguments>
</rabbit:queue>

By default, the arguments are assumed to be strings. For arguments of other types, the type needs to be provided.

<rabbit:queue name="withArguments">
    <rabbit:queue-arguments value-type="java.lang.Long">
        <entry key="x-message-ttl" value="100"/>
    </rabbit:queue-arguments>
</rabbit:queue>

When providing arguments of mixed types, the type is provided for each entry element:

<rabbit:queue name="withArguments">
    <rabbit:queue-arguments>
        <entry key="x-message-ttl">
            <value type="java.lang.Long">100</value>
        </entry>
        <entry key="x-ha-policy" value="all"/>
    </rabbit:queue-arguments>
</rabbit:queue>

With Spring Framework 3.2 and later, this can be declared a little more succinctly:

<rabbit:queue name="withArguments">
    <rabbit:queue-arguments>
        <entry key="x-message-ttl" value="100" value-type="java.lang.Long"/>
        <entry key="x-ha-policy" value="all"/>
    </rabbit:queue-arguments>
</rabbit:queue>
[Important]Important

The RabbitMQ broker will not allow declaration of a queue with mismatched arguments. For example, if a queue already exists with no time to live argument, and you attempt to declare it with, say, key="x-message-ttl" value="100", an exception will be thrown.

By default, the RabbitAdmin will immediately stop processing all declarations when any exception occurs; this could cause downstream issues - such as a listener container failing to initialize because another queue (defined after the one in error) is not declared.

This behavior can be modified by setting the ignore-declaration-exceptions attribute to true on the RabbitAdmin. This option instructs the RabbitAdmin to log the exception, and continue declaring other elements. When configuring the RabbitAdmin using java, this property is ignoreDeclarationExceptions. This is a global setting which applies to all elements, queues, exchanges and bindings have a similar property which applies to just those elements.

Prior to version 1.6, this property only took effect if an IOException occurred on the channel - such as when there is a mismatch between current and desired properties. Now, this property takes effect on any exception, including TimeoutException etc.

In addition, any declaration exceptions result in the publishing of a DeclarationExceptionEvent, which is an ApplicationEvent that can be consumed by any ApplicationListener in the context. The event contains a reference to the admin, the element that was being declared, and the Throwable.

Starting with version 1.3 the HeadersExchange can be configured to match on multiple headers; you can also specify whether any or all headers must match:

<rabbit:headers-exchange name="headers-test">
    <rabbit:bindings>
        <rabbit:binding queue="bucket">
            <rabbit:binding-arguments>
                <entry key="foo" value="bar"/>
                <entry key="baz" value="qux"/>
                <entry key="x-match" value="all"/>
            </rabbit:binding-arguments>
        </rabbit:binding>
    </rabbit:bindings>
</rabbit:headers-exchange>

Starting with version 1.6 Exchanges can be configured with an internal flag (defaults to false) and such an Exchange will be properly configured on the Broker via a RabbitAdmin (if one is present in the application context). If the internal flag is true for an exchange, RabbitMQ will not allow clients to use the exchange. This is useful for a dead letter exchange, or exchange-to-exchange binding, where you don’t wish the exchange to be used directly by publishers.

To see how to use Java to configure the AMQP infrastructure, look at the Stock sample application, where there is the @Configuration class AbstractStockRabbitConfiguration which in turn has RabbitClientConfiguration and RabbitServerConfiguration subclasses. The code for AbstractStockRabbitConfiguration is shown below

@Configuration
public abstract class AbstractStockAppRabbitConfiguration {

    @Bean
    public ConnectionFactory connectionFactory() {
        CachingConnectionFactory connectionFactory =
            new CachingConnectionFactory("localhost");
        connectionFactory.setUsername("guest");
        connectionFactory.setPassword("guest");
        return connectionFactory;
    }

    @Bean
    public RabbitTemplate rabbitTemplate() {
        RabbitTemplate template = new RabbitTemplate(connectionFactory());
        template.setMessageConverter(jsonMessageConverter());
        configureRabbitTemplate(template);
        return template;
    }

    @Bean
    public MessageConverter jsonMessageConverter() {
        return new Jackson2JsonMessageConverter();
    }

    @Bean
    public TopicExchange marketDataExchange() {
        return new TopicExchange("app.stock.marketdata");
    }

    // additional code omitted for brevity

}

In the Stock application, the server is configured using the following @Configuration class:

@Configuration
public class RabbitServerConfiguration extends AbstractStockAppRabbitConfiguration  {

    @Bean
    public Queue stockRequestQueue() {
        return new Queue("app.stock.request");
    }
}

This is the end of the whole inheritance chain of @Configuration classes. The end result is the the TopicExchange and Queue will be declared to the broker upon application startup. There is no binding of the TopicExchange to a queue in the server configuration, as that is done in the client application. The stock request queue however is automatically bound to the AMQP default exchange - this behavior is defined by the specification.

The client @Configuration class is a little more interesting and is shown below.

@Configuration
public class RabbitClientConfiguration extends AbstractStockAppRabbitConfiguration {

    @Value("${stocks.quote.pattern}")
    private String marketDataRoutingKey;

    @Bean
    public Queue marketDataQueue() {
        return amqpAdmin().declareQueue();
    }

    /**
     * Binds to the market data exchange.
     * Interested in any stock quotes
     * that match its routing key.
     */
    @Bean
    public Binding marketDataBinding() {
        return BindingBuilder.bind(
                marketDataQueue()).to(marketDataExchange()).with(marketDataRoutingKey);
    }

    // additional code omitted for brevity

}

The client is declaring another queue via the declareQueue() method on the AmqpAdmin, and it binds that queue to the market data exchange with a routing pattern that is externalized in a properties file.

Builder API for Queues and Exchanges

Version 1.6 introduces a convenient fluent API for configuring Queue and Exchange objects when using Java configuration:

@Bean
public Queue queue() {
    return QueueBuilder.nonDurable("foo")
        .autoDelete()
        .exclusive()
        .withArgument("foo", "bar")
        .build();
}

@Bean
public Exchange exchange() {
  return ExchangeBuilder.directExchange("foo")
      .autoDelete()
      .internal()
      .withArgument("foo", "bar")
      .build();
}

See the javadocs for org.springframework.amqp.core.QueueBuilder and org.springframework.amqp.core.ExchangeBuilder for more information.

Starting with version 2.0, the ExchangeBuilder now creates durable exchanges by default, to be consistent with the simple constructors on the individual AbstractExchange classes. To make a non-durable exchange with the builder, use .durable(false) before invoking .build(). The durable() method with no parameter is no longer provided.

Declaring Collections of Exchanges, Queues, Bindings

Starting with version 1.5, it is now possible to declare multiple entities with one @Bean, by returning a collection.

Only collections where the first element is a Declarable are considered, and only Declarable elements from such collections are processed.

@Configuration
public static class Config {

    @Bean
    public ConnectionFactory cf() {
        return new CachingConnectionFactory("localhost");
    }

    @Bean
    public RabbitAdmin admin(ConnectionFactory cf) {
        return new RabbitAdmin(cf);
    }

    @Bean
    public DirectExchange e1() {
    	return new DirectExchange("e1", false, true);
    }

    @Bean
    public Queue q1() {
    	return new Queue("q1", false, false, true);
    }

    @Bean
    public Binding b1() {
    	return BindingBuilder.bind(q1()).to(e1()).with("k1");
    }

    @Bean
    public List<Exchange> es() {
    	return Arrays.<Exchange>asList(
    			new DirectExchange("e2", false, true),
    			new DirectExchange("e3", false, true)
    	);
    }

    @Bean
    public List<Queue> qs() {
    	return Arrays.asList(
    			new Queue("q2", false, false, true),
    			new Queue("q3", false, false, true)
    	);
    }

    @Bean
    public List<Binding> bs() {
    	return Arrays.asList(
    			new Binding("q2", DestinationType.QUEUE, "e2", "k2", null),
    			new Binding("q3", DestinationType.QUEUE, "e3", "k3", null)
    	);
    }

    @Bean
    public List<Declarable> ds() {
    	return Arrays.<Declarable>asList(
    			new DirectExchange("e4", false, true),
    			new Queue("q4", false, false, true),
    			new Binding("q4", DestinationType.QUEUE, "e4", "k4", null)
    	);
    }

}

Conditional Declaration

By default, all queues, exchanges, and bindings are declared by all RabbitAdmin instances (that have auto-startup="true") in the application context.

[Note]Note

Starting with the 1.2 release, it is possible to conditionally declare these elements. This is particularly useful when an application connects to multiple brokers and needs to specify with which broker(s) a particular element should be declared.

The classes representing these elements implement Declarable which has two methods: shouldDeclare() and getDeclaringAdmins(). The RabbitAdmin uses these methods to determine whether a particular instance should actually process the declarations on its Connection.

The properties are available as attributes in the namespace, as shown in the following examples.

<rabbit:admin id="admin1" connection-factory="CF1" />

<rabbit:admin id="admin2" connection-factory="CF2" />

<rabbit:queue id="declaredByBothAdminsImplicitly" />

<rabbit:queue id="declaredByBothAdmins" declared-by="admin1, admin2" />

<rabbit:queue id="declaredByAdmin1Only" declared-by="admin1" />

<rabbit:queue id="notDeclaredByAny" auto-declare="false" />

<rabbit:direct-exchange name="direct" declared-by="admin1, admin2">
	<rabbit:bindings>
		<rabbit:binding key="foo" queue="bar"/>
	</rabbit:bindings>
</rabbit:direct-exchange>
[Note]Note

The auto-declare attribute is true by default and if the declared-by is not supplied (or is empty) then all RabbitAdmin s will declare the object (as long as the admin’s auto-startup attribute is true; the default).

Similarly, you can use Java-based @Configuration to achieve the same effect. In this example, the components will be declared by admin1 but not admin2:

@Bean
public RabbitAdmin admin() {
    RabbitAdmin rabbitAdmin = new RabbitAdmin(cf1());
    rabbitAdmin.afterPropertiesSet();
    return rabbitAdmin;
}

@Bean
public RabbitAdmin admin2() {
    RabbitAdmin rabbitAdmin = new RabbitAdmin(cf2());
    rabbitAdmin.afterPropertiesSet();
    return rabbitAdmin;
}

@Bean
public Queue queue() {
    Queue queue = new Queue("foo");
    queue.setAdminsThatShouldDeclare(admin());
    return queue;
}

@Bean
public Exchange exchange() {
    DirectExchange exchange = new DirectExchange("bar");
    exchange.setAdminsThatShouldDeclare(admin());
    return exchange;
}

@Bean
public Binding binding() {
    Binding binding = new Binding("foo", DestinationType.QUEUE, exchange().getName(), "foo", null);
    binding.setAdminsThatShouldDeclare(admin());
    return binding;
}

A Note On "id" and "name" Attributes

The name attribute on <rabbit:queue/> and <rabbit:exchange/> elements reflects the name of the entity in the broker. For queues, if the name is omitted, an anonymous queue is created (see the section called “AnonymousQueue” below).

In versions prior to 2.0, the name was also registered as a bean name alias (similar to name on <bean/> elements).

This caused two problems:

  • it prevented the declaration of a queue and exchange with the same name
  • the alias was not resolved if it contained a SpEL expression (#{...})

Starting with version 2.0, if you declare one of these elements with both an id and a name attribute, the name will no longer be declared as a bean name alias. If you wish to declare a queue and exchange with the same name, you must provide an id.

There is no change if the element has just a name attribute, the bean can still be referenced by the name, for example in binding declarations, but you still can’t reference it if the name contains SpEL - provide an id for reference purposes.

AnonymousQueue

In general, when needing a uniquely-named, exclusive, auto-delete queue, it is recommended that the AnonymousQueue is used instead of broker-defined queue names (using "" as a Queue name will cause the broker to generate the queue name).

This is because:

  1. The queues are actually declared when the connection to the broker is established; this is long after the beans are created and wired together; beans using the queue need to know its name. In fact, the broker might not even be running when the app is started.
  2. If the connection to the broker is lost for some reason, the admin will re-declare the AnonymousQueue with the same name. If we used broker-declared queues, the queue name would change.

You can control the format of the queue name used by AnonymousQueue s.

By default, the queue name is prefixed by spring.gen- followed by a base64 representation of the UUID, for example: spring.gen-MRBv9sqISkuCiPfOYfpo4g.

You can provide an AnonymousQueue.NamingStrategy implementation in a constructor argument.

@Bean
public Queue anon1() {
    return new AnonymousQueue();
}

@Bean
public Queue anon2() {
    return new AnonymousQueue(new AnonymousQueue.Base64UrlNamingStrategy("foo-"));
}

@Bean
public Queue anon3() {
    return new AnonymousQueue(AnonymousQueue.UUIDNamingStrategy.DEFAULT);
}

The first will generate a queue name prefixed by spring.gen- followed by a base64 representation of the UUID, for example: spring.gen-MRBv9sqISkuCiPfOYfpo4g. The second will generate a queue name prefixed by foo- followed by a base64 representation of the UUID. The third will generate a name using just the UUID (no base64 conversion), e.g. f20c818a-006b-4416-bf91-643590fedb0e.

The base64 encoding uses the "URL and Filename Safe Alphabet" from RFC 4648; trailing padding characters (=) are removed.

You can provide your own naming strategy, whereby you can include other information (e.g. application, client host) in the queue name.

The naming strategy can be specified when using XML configuration; the naming-strategy attribute is present on the <rabbit:queue> element for a bean reference that implements AnonymousQueue.NamingStrategy.

<rabbit:queue id="uuidAnon" />

<rabbit:queue id="springAnon" naming-strategy="uuidNamer" />

<rabbit:queue id="customAnon" naming-strategy="customNamer" />

<bean id="uuidNamer" class="org.springframework.amqp.core.AnonymousQueue.UUIDNamingStrategy" />

<bean id="customNamer" class="org.springframework.amqp.core.AnonymousQueue.Base64UrlNamingStrategy">
    <constructor-arg value="custom.gen-" />
</bean>

The first creates names like spring.gen-MRBv9sqISkuCiPfOYfpo4g. The second creates names with a String representation of a UUID. The third creates names like custom.gen-MRBv9sqISkuCiPfOYfpo4g.

Of course, you can provide your own naming strategy bean.

3.1.11 Delayed Message Exchange

Version 1.6 introduces support for the Delayed Message Exchange Plugin

[Note]Note

The plugin is currently marked as experimental but has been available for over a year (at the time of writing). If changes to the plugin make it necessary, we will add support for such changes as soon as practical. For that reason, this support in Spring AMQP should be considered experimental, too. This functionality was tested with RabbitMQ 3.6.0 and version 0.0.1 of the plugin.

To use a RabbitAdmin to declare an exchange as delayed, simply set the delayed property on the exchange bean to true. The RabbitAdmin will use the exchange type (Direct, Fanout etc) to set the x-delayed-type argument and declare the exchange with type x-delayed-message.

The delayed property (default false) is also available when configuring exchange beans using XML.

<rabbit:topic-exchange name="topic" delayed="true" />

To send a delayed message, it’s simply a matter of setting the x-delay header, via the MessageProperties:

MessageProperties properties = new MessageProperties();
properties.setDelay(15000);
template.send(exchange, routingKey,
        MessageBuilder.withBody("foo".getBytes()).andProperties(properties).build());

or

rabbitTemplate.convertAndSend(exchange, routingKey, "foo", new MessagePostProcessor() {

    @Override
    public Message postProcessMessage(Message message) throws AmqpException {
        message.getMessageProperties().setDelay(15000);
        return message;
    }

});

To check if a message was delayed, use the getReceivedDelay() method on the MessageProperties. It is a separate property to avoid unintended propagation to an output message generated from an input message.

3.1.12 RabbitMQ REST API

When the management plugin is enabled, the RabbitMQ server exposes a REST API to monitor and configure the broker. A Java Binding for the API is now provided. In general, you can use that API directly, but a convenience wrapper is provided to use the familiar Spring AMQP Queue, Exchange, and Binding domain objects with the API. Much more information is available for these objects when using the com.rabbitmq.http.client.Client API directly (QueueInfo, ExchangeInfo, and BindingInfo respectively). The following operations are available on the RabbitManagementTemplate:

public interface AmqpManagementOperations {

    void addExchange(Exchange exchange);

    void addExchange(String vhost, Exchange exchange);

    void purgeQueue(Queue queue);

    void purgeQueue(String vhost, Queue queue);

    void deleteQueue(Queue queue);

    void deleteQueue(String vhost, Queue queue);

    Queue getQueue(String name);

    Queue getQueue(String vhost, String name);

    List<Queue> getQueues();

    List<Queue> getQueues(String vhost);

    void addQueue(Queue queue);

    void addQueue(String vhost, Queue queue);

    void deleteExchange(Exchange exchange);

    void deleteExchange(String vhost, Exchange exchange);

    Exchange getExchange(String name);

    Exchange getExchange(String vhost, String name);

    List<Exchange> getExchanges();

    List<Exchange> getExchanges(String vhost);

    List<Binding> getBindings();

    List<Binding> getBindings(String vhost);

    List<Binding> getBindingsForExchange(String vhost, String exchange);

}

Refer to the javadocs for more information.

3.1.13 Exception Handling

Many operations with the RabbitMQ Java client can throw checked Exceptions. For example, there are a lot of cases where IOExceptions may be thrown. The RabbitTemplate, SimpleMessageListenerContainer, and other Spring AMQP components will catch those Exceptions and convert into one of the Exceptions within our runtime hierarchy. Those are defined in the org.springframework.amqp package, and AmqpException is the base of the hierarchy.

When a listener throws an exception, it is wrapped in a ListenerExecutionFailedException and, normally the message is rejected and requeued by the broker. Setting defaultRequeueRejected to false will cause messages to be discarded (or routed to a dead letter exchange). As discussed in the section called “Message Listeners and the Asynchronous Case”, the listener can throw an AmqpRejectAndDontRequeueException to conditionally control this behavior.

However, there is a class of errors where the listener cannot control the behavior. When a message that cannot be converted is encountered (for example an invalid content_encoding header), some exceptions are thrown before the message reaches user code. With defaultRequeueRejected set to true (default), such messages would be redelivered over and over. Before version 1.3.2, users needed to write a custom ErrorHandler, as discussed in Section 3.1.13, “Exception Handling” to avoid this situation.

Starting with version 1.3.2, the default ErrorHandler is now a ConditionalRejectingErrorHandler which will reject (and not requeue) messages that fail with an irrecoverable error:

  • o.s.amqp...MessageConversionException
  • o.s.messaging...MessageConversionException
  • o.s.messaging...MethodArgumentNotValidException
  • o.s.messaging...MethodArgumentTypeMismatchException
  • java.lang.NoSuchMethodException
  • java.lang.ClassCastException

The first can be thrown when converting the incoming message payload using a MessageConverter. The second may be thrown by the conversion service if additional conversion is required when mapping to a @RabbitListener method. The third may be thrown if validation (e.g. @Valid) is used in the listener and the validation fails. The fourth may be thrown if the inbound message was converted to a type that is not correct for the target method. For example, the parameter is declared as Message<Foo> but Message<Bar> is received.

The fifth and sixth were added in version 1.6.3.

An instance of this error handler can be configured with a FatalExceptionStrategy so users can provide their own rules for conditional message rejection, e.g. a delegate implementation to the BinaryExceptionClassifier from Spring Retry (the section called “Message Listeners and the Asynchronous Case”). In addition, the ListenerExecutionFailedException now has a failedMessage property which can be used in the decision. If the FatalExceptionStrategy.isFatal() method returns true, the error handler throws an AmqpRejectAndDontRequeueException. The default FatalExceptionStrategy logs a warning message when an exception is determined to be fatal.

Since version 1.6.3 a convenient way to add user exceptions to the fatal list is to subclass ConditionalRejectingErrorHandler.DefaultExceptionStrategy and override the method isUserCauseFatal(Throwable cause) to return true for fatal exceptions.

3.1.14 Transactions

Introduction

The Spring Rabbit framework has support for automatic transaction management in the synchronous and asynchronous use cases with a number of different semantics that can be selected declaratively, as is familiar to existing users of Spring transactions. This makes many if not most common messaging patterns very easy to implement.

There are two ways to signal the desired transaction semantics to the framework. In both the RabbitTemplate and SimpleMessageListenerContainer there is a flag channelTransacted which, 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 signaling a rollback. Another signal is to provide an external transaction with one of Spring’s PlatformTransactionManager implementations as a context for the ongoing operation. 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).

The channelTransacted flag is a configuration time setting: it is declared and processed once when the AMQP components are created, usually at application startup. The external transaction is more dynamic in principle because the system responds to the current Thread state at runtime, but in practice is often also a configuration setting, when the transactions are layered onto an application declaratively.

For synchronous use cases with RabbitTemplate the external transaction is provided by the caller, either declaratively or imperatively according to taste (the usual Spring transaction model). An example of a declarative approach (usually preferred because it is non-invasive), where the template has been configured with channelTransacted=true:

@Transactional
public void doSomething() {
    String incoming = rabbitTemplate.receiveAndConvert();
    // do some more database processing...
    String outgoing = processInDatabaseAndExtractReply(incoming);
    rabbitTemplate.convertAndSend(outgoing);
}

A String payload is received, converted and sent as a message body inside a method marked as @Transactional, so if the database processing fails with an exception, the incoming message will be returned to the broker, and the outgoing message will not be sent. This applies to any operations with the RabbitTemplate inside a chain of transactional methods (unless the Channel is directly manipulated to commit the transaction early for instance).

For asynchronous use cases with SimpleMessageListenerContainer if an external transaction is needed it has to be requested by the container when it sets up the listener. To signal that an external transaction is required the user provides an implementation of PlatformTransactionManager to the container when it is configured. For example:

@Configuration
public class ExampleExternalTransactionAmqpConfiguration {

    @Bean
    public SimpleMessageListenerContainer messageListenerContainer() {
        SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();
        container.setConnectionFactory(rabbitConnectionFactory());
        container.setTransactionManager(transactionManager());
        container.setChannelTransacted(true);
        container.setQueueName("some.queue");
        container.setMessageListener(exampleListener());
        return container;
    }

}

In the example above, the transaction manager is added as a dependency injected from another bean definition (not shown), and the channelTransacted flag is also set to true. The effect is that if the listener fails with an exception the transaction will be rolled back, and the message will also be returned to the broker. Significantly, if the transaction fails to commit (e.g. a database constraint error, or connectivity problem), then the AMQP transaction will also be rolled back, and the message will be returned to the broker. This is sometimes known as a Best Efforts 1 Phase Commit, and is a very powerful pattern for reliable messaging. If the channelTransacted flag was set to false in the example above, which is the default, then the external transaction would still be provided for the listener, but all messaging operations would be auto-acked, so the effect is to commit the messaging operations even on a rollback of the business operation.

Conditional Rollback

Prior to version 1.6.6, adding a rollback rule to a container’s transactionAttribute, when using an external transaction manager (e.g. JDBC) had no effect; exceptions always rolled back the transaction.

Also, when using a transaction advice in the container’s advice chain, conditional rollback was not very useful because all listener exceptions are wrapped in a ListenerExecutionFailedException.

The first problem has been corrected and the rules are now applied properly. Further, the ListenerFailedRuleBasedTransactionAttribute is now provided; it is a subclass of RuleBasedTransactionAttribute, with the only difference being that it is aware of the ListenerExecutionFailedException and uses the cause of such exceptions for the rule. This transaction attribute can be used directly in the container, or via a transaction advice.

An example of using this rule follows:

@Bean
public AbstractMessageListenerContainer container() {
    ...
    container.setTransactionManager(transactionManager);
    RuleBasedTransactionAttribute transactionAttribute =
        new ListenerFailedRuleBasedTransactionAttribute();
    transactionAttribute.setRollbackRules(Collections.singletonList(
        new NoRollbackRuleAttribute(DontRollBackException.class)));
    container.setTransactionAttribute(transactionAttribute);
    ...
}

A note on Rollback of Received Messages

AMQP transactions only apply to messages and acks sent to the broker, so when there is a rollback of a Spring transaction and a message has been received, what Spring AMQP has to do is not just rollback the transaction, but also manually reject the message (sort of a nack, but that’s not what the specification calls it). The action taken on message rejection is independent of transactions and depends on the defaultRequeueRejected property (default true). For more information about rejecting failed messages, see the section called “Message Listeners and the Asynchronous Case”.

For more information about RabbitMQ transactions, and their limitations, refer to RabbitMQ Broker Semantics.

[Note]Note

Prior to RabbitMQ 2.7.0, such messages (and any that are unacked when a channel is closed or aborts) went to the back of the queue on a Rabbit broker, since 2.7.0, rejected messages go to the front of the queue, in a similar manner to JMS rolled back messages.

[Note]Note

Previously, message requeue on transaction rollback was inconsistent between local transactions and when a TransactionManager was provided. In the former case, the normal requeue logic (AmqpRejectAndDontRequeueException or defaultRequeueRejected=false) applied (see the section called “Message Listeners and the Asynchronous Case”); with a transaction manager, the message was unconditionally requeued on rollback. Starting with version 2.0, the behavior is consistent and the normal requeue logic is applied in both cases. To revert to the previous behavior, set the container’s alwaysRequeueWithTxManagerRollback property to true. See Section 3.1.15, “Message Listener Container Configuration”.

Using the RabbitTransactionManager

The RabbitTransactionManager is an alternative to executing Rabbit operations within, and synchronized with, external transactions. This Transaction Manager is an implementation of the PlatformTransactionManager interface and should be used with a single Rabbit ConnectionFactory.

[Important]Important

This strategy is not able to provide XA transactions, for example in order to share transactions between messaging and database access.

Application code is required to retrieve the transactional Rabbit resources via ConnectionFactoryUtils.getTransactionalResourceHolder(ConnectionFactory, boolean) instead of a standard Connection.createChannel() call with subsequent Channel creation. When using Spring AMQP’s RabbitTemplate, it will autodetect a thread-bound Channel and automatically participate in its transaction.

With Java Configuration you can setup a new RabbitTransactionManager using:

@Bean
public RabbitTransactionManager rabbitTransactionManager() {
    return new RabbitTransactionManager(connectionFactory);
}

If you prefer using XML configuration, declare the following bean in your XML Application Context file:

<bean id="rabbitTxManager"
      class="org.springframework.amqp.rabbit.transaction.RabbitTransactionManager">
    <property name="connectionFactory" ref="connectionFactory"/>
</bean>

3.1.15 Message Listener Container Configuration

There are quite a few options for configuring a SimpleMessageListenerContainer (SMLC) and DirectMessageListenerContainer (DMLC) related to transactions and quality of service, and some of them interact with each other. Properties that apply to the SMLC or DMLC are indicated by the check mark in the appropriate column. See the section called “Choosing a Container” for information to help you decide which container is appropriate for your application.

The table below shows the container property names and their equivalent attribute names (in parentheses) when using the namespace to configure a <rabbit:listener-container/>. The type attribute on that element can be simple (default) or direct to specify an SMLC or DMLC respectively.

Some properties are not exposed by the namespace; indicated by N/A for the attribute.

Table 3.3. Configuration options for a message listener container

Property (Attribute)DescriptionSMLCDMLC
(group)

This is only available when using the namespace. When specified, a bean of type Collection<MessageListenerContainer> is registered with this name, and the container for each <listener/> element is added to the collection. This allows, for example, starting/stopping the group of containers by iterating over the collection. If multiple <listener-container/> elements have the same group value, the containers in the collection is an aggregate of all containers so designated.

tickmark
tickmark
channelTransacted
(channel-transacted)

Boolean flag to signal that all messages should be acknowledged in a transaction (either manually or automatically)

tickmark
tickmark
acknowledgeMode
(acknowledge)
  • NONE = no acks will be sent (incompatible with channelTransacted=true). RabbitMQ calls this "autoack" because the broker assumes all messages are acked without any action from the consumer.
  • MANUAL = the listener must acknowledge all messages by calling Channel.basicAck().
  • AUTO = the container will acknowledge the message automatically, unless the MessageListener throws an exception. Note that acknowledgeMode is complementary to channelTransacted - if the channel is transacted then the broker requires a commit notification in addition to the ack. This is the default mode. See also txSize.
tickmark
tickmark
transactionManager
(transaction-manager)

External transaction manager for the operation of the listener. Also complementary to channelTransacted - if the Channel is transacted then its transaction will be synchronized with the external transaction.

tickmark
tickmark
prefetchCount
(prefetch)

The number of unacknowledged messages that can be outstanding at each consumer. The higher this is the faster the messages can be delivered, but the higher the risk of non-sequential processing. Ignored if the acknowledgeMode is NONE. This will be increased, if necessary, to match the txSize or messagePerAck. Defaults to 250 since 2.0; set to 1 to revert to previous behavior.

[Important]Important

There are scenarios where the prefetch value should be low: for example, with large messages, especially if the processing is slow (messages could add up to a large amount of memory in the client process), and if strict message ordering is necessary (the prefetch value should be set back to 1 in this case). Also, with low-volume messaging and multiple consumers (including concurrency within a single listener container instance), you may wish to reduce the prefetch to get a more even distribution of messages across consumers.

tickmark
tickmark
shutdownTimeout
(N/A)

When a container shuts down (e.g. if its enclosing ApplicationContext is closed) it waits for in-flight messages to be processed up to this limit. Defaults to 5 seconds.

tickmark
tickmark
forceCloseChannel
(N/A)

If the consumers don’t respond to a shutdown within shutdownTimeout, if this is true, the channel will be closed, causing any unacked messages to be requeued. Default true since 2.0; set to false to revert to previous behavior.

tickmark
tickmark
txSize
(transaction-size)

When used with acknowledgeMode AUTO, the container will attempt to process up to this number of messages before sending an ack (waiting for each one up to the receive timeout setting). This is also when a transactional channel is committed. If the prefetchCount is less than the txSize, it will be increased to match the txSize.

tickmark
 
messagesPerAck
(N/A)

The number of messages to receive between acks. Use this to reduce the number of acks sent to the broker (at the cost of increasing the possibility of redelivered messages). Generally, you should only set this property on high-volume listener containers. If this is set, and a message is rejected (exception thrown), pending acks will be acknowledged and the failed message rejected. Not allowed with transacted channels. If the prefetchCount is less than the messagesPerAck, it will be increased to match the messagesPerAck. Default: ack every message. See also ackTimeout.

 
tickmark
ackTimeout
(N/A)

When messagesPerAck is set, this timeout is used as an alternative to send an ack. When a new message arrives, the count of unacked messages is compared to messagesPerAck, and the time since the last ack is compared to this value; if either condition is true, the message is acknowledged. When no new messages arrive, and there are unacked messages, this timeout is approximate since the condition is only checked each monitorInterval. See also messagesPerAck, monitorInterval.

 
tickmark
receiveTimeout
(receive-timeout)

The maximum time to wait for each message. If acknowledgeMode=NONE this has very little effect - the container just spins round and asks for another message. It has the biggest effect for a transactional Channel with txSize > 1, since it can cause messages already consumed not to be acknowledged until the timeout expires.

tickmark
 
autoStartup
(auto-startup)

Flag to indicate that the container should start when the ApplicationContext does (as part of the SmartLifecycle callbacks which happen after all beans are initialized). Defaults to true, but set it to false if your broker might not be available on startup, and then call start() later manually when you know the broker is ready.

tickmark
tickmark
phase
(phase)

When autoStartup is true, the lifecycle phase within which this container should start and stop. The lower the value the earlier this container will start and the later it will stop. The default is Integer.MAX_VALUE meaning the container will start as late as possible and stop as soon as possible.

tickmark
tickmark
adviceChain
(advice-chain)

An array of AOP Advice to apply to the listener execution. This can be used to apply additional cross cutting concerns such as automatic retry in the event of broker death. Note that simple re-connection after an AMQP error is handled by the CachingConnectionFactory, as long as the broker is still alive.

tickmark
tickmark
taskExecutor
(task-executor)

A reference to a Spring TaskExecutor (or standard JDK 1.5+ Executor) for executing listener invokers. Default is a SimpleAsyncTaskExecutor, using internally managed threads.

tickmark
tickmark
errorHandler
(error-handler)

A reference to an ErrorHandler strategy for handling any uncaught Exceptions that may occur during the execution of the MessageListener. Default: ConditionalRejectingErrorHandler

tickmark
tickmark
consumersPerQueue
(consumers-per-queue)

The number of consumers to create for each condigured queue. See Section 3.1.16, “Listener Concurrency”.

 
tickmark
concurrentConsumers
(concurrency)

The number of concurrent consumers to initially start for each listener. See Section 3.1.16, “Listener Concurrency”.

tickmark
 
maxConcurrent
Consumers
(max-concurrency)

The maximum number of concurrent consumers to start, if needed, on demand. Must be greater than or equal to concurrentConsumers. See Section 3.1.16, “Listener Concurrency”.

tickmark
 
concurrency
(N/A)

m-n The range of concurrent consumers for each listener (min, max). If only n is provided, n is a fixed number of consumers. See Section 3.1.16, “Listener Concurrency”.

tickmark
 
startConsumerMin
Interval
(min-start-interval)

The time in milliseconds which must elapse before each new consumer is started on demand. See Section 3.1.16, “Listener Concurrency”. Default 10000 (10 seconds).

tickmark
 
stopConsumerMin
Interval
(min-stop-interval)

The time in milliseconds which must elapse before a consumer is stopped, since the last consumer was stopped, when an idle consumer is detected. See Section 3.1.16, “Listener Concurrency”. Default 60000 (1 minute).

tickmark
 
consecutiveActive
Trigger
(min-consecutive-active)

The minimum number of consecutive messages received by a consumer, without a receive timeout occurring, when considering starting a new consumer. Also impacted by txSize. See Section 3.1.16, “Listener Concurrency”. Default 10.

tickmark
 
consecutiveIdle
Trigger
(min-consecutive-idle)

The minimum number of receive timeouts a consumer must experience before considering stopping a consumer. Also impacted by txSize. See Section 3.1.16, “Listener Concurrency”. Default 10.

tickmark
 
connectionFactory
(connection-factory)

A reference to the ConnectionFactory; when configuring using the XML namespace, the default referenced bean name is "rabbitConnectionFactory".

tickmark
tickmark
defaultRequeue
Rejected
(requeue-rejected)

Determines whether messages that are rejected because the listener threw an exception should be requeued or not. Default true.

tickmark
tickmark
recoveryInterval
(recovery-interval)

Determines the time in milliseconds between attempts to start a consumer if it fails to start for non-fatal reasons. Default 5000. Mutually exclusive with recoveryBackOff.

tickmark
tickmark
recoveryBackOff
(recovery-back-off)

Specifies the BackOff for intervals between attempts to start a consumer if it fails to start for non-fatal reasons. Default is FixedBackOff with unlimited retries every 5 seconds. Mutually exclusive with recoveryInterval.

tickmark
tickmark
exclusive
(exclusive)

Determines whether the single consumer in this container has exclusive access to the queue(s). The concurrency of the container must be 1 when this is true. If another consumer has exclusive access, the container will attempt to recover the consumer, according to the recovery-interval or recovery-back-off. When using the namespace, this attribute appears on the <rabbit:listener/> element along with the queue names. Default false.

tickmark
tickmark
rabbitAdmin
(admin)

When a listener container listens to at least one auto-delete queue and it is found to be missing during startup, the container uses a RabbitAdmin to declare the queue and any related bindings and exchanges. If such elements are configured to use conditional declaration (see the section called “Conditional Declaration”), the container must use the admin that was configured to declare those elements. Specify that admin here; only required when using auto-delete queues with conditional declaration. If you do not wish the auto-delete queue(s) to be declared until the container is started, set auto-startup to false on the admin. Defaults to a RabbitAdmin that will declare all non-conditional elements.

tickmark
tickmark
missingQueuesFatal
(missing-queues-fatal)

When set to true (default), if none of the configured queues are available on the broker, it is considered fatal. This causes the application context to fail to initialize during startup; also, when the queues are deleted while the container is running, by default, the consumers make 3 retries to connect to the queues (at 5 second intervals) and stop the container if these attempts fail.

This was not configurable in previous versions.

When set to false, after making the 3 retries, the container will go into recovery mode, as with other problems, such as the broker being down. The container will attempt to recover according to the recoveryInterval property. During each recovery attempt, each consumer will again try 4 times to passively declare the queues at 5 second intervals. This process will continue indefinitely.

You can also use a properties bean to set the property globally for all containers, as follows:

<util:properties id="spring.amqp.global.properties">
    <prop key="mlc.missing.queues.fatal">false</prop>
</util:properties>

This global property will not be applied to any containers that have an explicit missingQueuesFatal property set.

The default retry properties (3 retries at 5 second intervals) can be overridden using the properties below.

tickmark
tickmark
possibleAuthenticationFailureFatal
(possible-authentication-failure-fatal)

When set to true (default), if a PossibleAuthenticationFailureException is thrown during connection, it is considered fatal. This causes the application context to fail to initialize during startup.

Since version 2.0.

When set to false, after making the 3 retries, the container will go into recovery mode, as with other problems, such as the broker being down. The container will attempt to recover according to the recoveryInterval property. During each recovery attempt, each consumer will again try 4 times to start. This process will continue indefinitely.

You can also use a properties bean to set the property globally for all containers, as follows:

<util:properties id="spring.amqp.global.properties">
    <prop key="mlc.possible.authentication.failure.fatal">false</prop>
</util:properties>

This global property will not be applied to any containers that have an explicit missingQueuesFatal property set.

The default retry properties (3 retries at 5 second intervals) can be overridden using the properties below.

tickmark
tickmark
mismatchedQueuesFatal
(mismatched-queues-fatal)

When the container starts, if this property is true (default: false), the container checks that all queues declared in the context are compatible with queues already on the broker. If mismatched properties (e.g. auto-delete) or arguments (e.g. x-message-ttl) exist, the container (and application context) will fail to start with a fatal exception.

If the problem is detected during recovery (e.g. after a lost connection), the container will be stopped.

There must be a single RabbitAdmin in the application context (or one specifically configured on the container using the rabbitAdmin property); otherwise this property must be false.

[Note]Note

If the broker is not available during initial startup, the container will start and the conditions will be checked when the connection is established.

[Important]Important

the check is done against all queues in the context, not just the queues that a particular listener is configured to use. If you wish to limit the checks to just those queues used by a container, you should configure a separate RabbitAdmin for the container, and provide a reference to it using the rabbitAdmin property. See the section called “Conditional Declaration” for more information.

tickmark
tickmark
autoDeclare
(auto-declare)

When set to true (default), the container will use a RabbitAdmin to redeclare all AMQP objects (Queues, Exchanges, Bindings), if it detects that at least one of its queues is missing during startup, perhaps because it’s an auto-delete or an expired queue, but the redeclaration will proceed if the queue is missing for any reason. To disable this behavior, set this property to false. Note that the container will fail to start if all of its queues are missing.

[Note]Note

Prior to version 1.6, if there was more than one admin in the context, the container would randomly select one. If there were no admins, it would create one internally. In either case, this could cause unexpected results. Starting with version 1.6, for autoDeclare to work, there must be exactly one RabbitAdmin in the context, or a reference to a specific instance must be configured on the container using the rabbitAdmin property.

tickmark
tickmark
declarationRetries
(declaration-retries)

The number of retry attempts when passive queue declaration fails. Passive queue declaration occurs when the consumer starts or, when consuming from multiple queues, when not all queues were available during initialization. When none of the configured queues can be passively declared (for any reason) after the retries are exhausted, the container behavior is controlled by the 'missingQueuesFatal` property above. Default: 3 retries (4 attempts).

tickmark
 
failedDeclaration
RetryInterval
(failed-declaration-retry-
interval)

The interval between passive queue declaration retry attempts. Passive queue declaration occurs when the consumer starts or, when consuming from multiple queues, when not all queues were available during initialization. Default: 5000 (5 seconds).

tickmark
tickmark
retryDeclaration
Interval
(missing-queue-retry-
interval)

If a subset of the configured queues are available during consumer initialization, the consumer starts consuming from those queues. The consumer will attempt to passively declare the missing queues using this interval. When this interval elapses, the declarationRetries and failedDeclarationRetryInterval will again be used. If there are still missing queues, the consumer will again wait for this interval before trying again. This process will continue indefinitely until all queues are available. Default: 60000 (1 minute).

tickmark
 
consumerTagStrategy
(consumer-tag-strategy)

Set an implementation of ConsumerTagStrategy, enabling the creation of a (unique) tag for each consumer.

tickmark
tickmark
idleEventInterval
(idle-event-interval)

See the section called “Detecting Idle Asynchronous Consumers”.

tickmark
tickmark
monitorInterval
(monitor-interval)

With the DMLC, a task is scheduled to run at this interval to monitor the state of the consumers and recover any that have failed.

 
tickmark
taskScheduler
(task-scheduler)

With the DMLC, the scheduler used to run the monitor task at the monitorInterval.

 
tickmark
exclusiveConsumer
ExceptionLogger
(N/A)

An exception logger used when an exclusive consumer can’t gain access to a queue. By default, this is logged at the WARN level.

tickmark
tickmark
statefulRetry
FatalWithNull
MessageId
(N/A)

When using a stateful retry advice; if a message with a missing messageId property is received, it is considered fatal for the consumer (it is stopped) by default. Set this to false, to discard (or route to a dead-letter queue) such messages.

tickmark
tickmark
alwaysRequeueWithTx
ManagerRollback
(N/A)

Set to true to always requeue messages on rollback when a transaction manager is configured.

tickmark
tickmark
noLocal
(N/A)

Set to true to disable delivery from the server to consumers messages published on the same channel’s connection.

tickmark
tickmark
afterReceivePostProcessors
(N/A)

An array of MessagePostProcessor s which are invoked, before invoking the listener. Post processors can implement PriorityOrdered, Ordered; the array is sorted with un-ordered members invoked last. If a post processor returns null, the message is discarded (and acknowledged, if appropriate).

tickmark
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3.1.16 Listener Concurrency

SimpleMessageListenerContainer

By default, the listener container will start a single consumer which will receive messages from the queue(s).

When examining the table in the previous section, you will see a number of properties/attributes that control concurrency. The simplest is concurrentConsumers, which simply creates that (fixed) number of consumers which will concurrently process messages.

Prior to version 1.3.0, this was the only setting available and the container had to be stopped and started again to change the setting.

Since version 1.3.0, you can now dynamically adjust the concurrentConsumers property. If it is changed while the container is running, consumers will be added or removed as necessary to adjust to the new setting.

In addition, a new property maxConcurrentConsumers has been added and the container will dynamically adjust the concurrency based on workload. This works in conjunction with four additional properties: consecutiveActiveTrigger, startConsumerMinInterval, consecutiveIdleTrigger, stopConsumerMinInterval. With the default settings, the algorithm to increase consumers works as follows:

If the maxConcurrentConsumers has not been reached and an existing consumer is active for 10 consecutive cycles AND at least 10 seconds has elapsed since the last consumer was started, a new consumer is started. A consumer is considered active if it received at least one message in txSize * receiveTimeout milliseconds.

With the default settings, the algorithm to decrease consumers works as follows:

If there are more than concurrentConsumers running and a consumer detects 10 consecutive timeouts (idle) AND the last consumer was stopped at least 60 seconds ago, a consumer will be stopped. The timeout depends on the receiveTimeout and the txSize properties. A consumer is considered idle if it receives no messages in txSize * receiveTimeout milliseconds. So, with the default timeout (1 second) and a txSize of 4, stopping a consumer will be considered after 40 seconds of idle time (4 timeouts correspond to 1 idle detection).

[Note]Note

Practically, consumers will only be stopped if the whole container is idle for some time. This is because the broker will share its work across all the active consumers.

A single channel is used by each consumer, regardless of the number of configured queues.

Starting with version 2.0 the concurrentConsumers and maxConcurrentConsumers properties can be set with the single property concurrency; e.g. "2-4".

DirectMessageListenerContainer

With this container, concurrency is based on the configured queues and consumersPerQueue. Each consumer for each queue uses a separate channel and the concurrency is controlled by the rabbit client library; it uses a pool of 5 threads by default; you can configure a taskExecutor to provide the required maximum concurrency.

3.1.17 Exclusive Consumer

Also starting with version 1.3, the listener container can be configured with a single exclusive consumer; this prevents other containers from consuming from the queue(s) until the current consumer is cancelled. The concurrency of such a container must be 1.

When using exclusive consumers, other containers will attempt to consume from the queue(s) according to the recoveryInterval property, and log a WARNing if the attempt fails.

3.1.18 Listener Container Queues

version 1.3 introduced a number of improvements for handling multiple queues in a listener container.

The container must be configured to listen on at least one queue; this was the case previously too, but now queues can be added and removed at runtime. The container will recycle (cancel and re-create) the consumers when any pre-fetched messages have been processed. See methods addQueues, addQueueNames, removeQueues and removeQueueNames. When removing queues, at least one queue must remain.

A consumer will now start if any of its queues are available - previously the container would stop if any queues were unavailable. Now, this is only the case if none of the queues are available. If not all queues are available, the container will attempt to passively declare (and consume from) the missing queue(s) every 60 seconds.

Also, if a consumer receives a cancel from the broker (for example if a queue is deleted) the consumer will attempt to recover and the recovered consumer will continue to process messages from any other configured queues. Previously a cancel on one queue cancelled the entire consumer and eventually the container would stop due to the missing queue.

If you wish to permanently remove a queue, you should update the container before or after deleting to queue, to avoid future attempts to consume from it.

3.1.19 Resilience: Recovering from Errors and Broker Failures

Introduction

Some of the key (and most popular) high-level features that Spring AMQP provides are to do with recovery and automatic re-connection in the event of a protocol error or broker failure. We have seen all the relevant components already in this guide, but it should help to bring them all together here and call out the features and recovery scenarios individually.

The primary reconnection features are enabled by the CachingConnectionFactory itself. It is also often beneficial to use the RabbitAdmin auto-declaration features. In addition, if you care about guaranteed delivery, you probably also need to use the channelTransacted flag in RabbitTemplate and SimpleMessageListenerContainer and also the AcknowledgeMode.AUTO (or manual if you do the acks yourself) in the SimpleMessageListenerContainer.

Automatic Declaration of Exchanges, Queues and Bindings

The RabbitAdmin component can declare exchanges, queues and bindings on startup. It does this lazily, through a ConnectionListener, so if the broker is not present on startup it doesn’t matter. The first time a Connection is used (e.g. by sending a message) the listener will fire and the admin features will be applied. A further benefit of doing the auto declarations in a listener is that if the connection is dropped for any reason (e.g. broker death, network glitch, etc.) they will be applied again when the connection is re-established.

[Note]Note

Queues declared this way must have fixed names; either explicitly declared, or generated by the framework for AnonymousQueue s. Anonymous queues are non-durable, exclusive, and auto-delete.

[Important]Important

Automatic declaration is only performed when the CachingConnectionFactory cache mode is CHANNEL (the default). This limitation exists because exclusive and auto-delete queues are bound to the connection.

See also the section called “RabbitMQ Automatic Connection/Topology recovery”.

Failures in Synchronous Operations and Options for Retry

If you lose your connection to the broker in a synchronous sequence using RabbitTemplate (for instance), then Spring AMQP will throw an AmqpException (usually but not always AmqpIOException). We don’t try to hide the fact that there was a problem, so you have to be able to catch and respond to the exception. The easiest thing to do if you suspect that the connection was lost, and it wasn’t your fault, is to simply try the operation again. You can do this manually, or you could look at using Spring Retry to handle the retry (imperatively or declaratively).

Spring Retry provides a couple of AOP interceptors and a great deal of flexibility to specify the parameters of the retry (number of attempts, exception types, backoff algorithm etc.). Spring AMQP also provides some convenience factory beans for creating Spring Retry interceptors in a convenient form for AMQP use cases, with strongly typed callback interfaces for you to implement custom recovery logic. See the Javadocs and properties of StatefulRetryOperationsInterceptor and StatelessRetryOperationsInterceptor for more detail. Stateless retry is appropriate if there is no transaction or if a transaction is started inside the retry callback. Note that stateless retry is simpler to configure and analyse than stateful retry, but it is not usually appropriate if there is an ongoing transaction which must be rolled back or definitely is going to roll back. A dropped connection in the middle of a transaction should have the same effect as a rollback, so for reconnection where the transaction is started higher up the stack, stateful retry is usually the best choice. Stateful retry needs a mechanism to uniquely identify a message. The simplest approach is to have the sender put a unique value in the MessageId message property. The provided message converters provide an option to do this - set createMessageIds to true. Otherwise, you can inject a MessageKeyGenerator implementation into the interceptor; the key generator must return a unique key for each message. In versions prior to version 2.0, a MissingMessageIdAdvice was provided which enabled messages without a messageId property to be retried exactly once (ignoring the retry settings). This advice is no longer provided since, along with spring-retry version 1.2, its functionality is built into the interceptor and message listener containers.

[Note]Note

For backwards compatibility, a message with a null message id is considered fatal for the consumer (consumer is stopped) by default (after one retry). To replicate the functionality provided by the MissingMessageIdAdvice, set the statefulRetryFatalWithNullMessageId property to false on the listener container. With that setting the consumer will continue to run and the message will be rejected (after one retry); it will be discarded, or routed to the dead letter queue, if so configured.

Starting with version 1.3, a builder API is provided to aid in assembling these interceptors using Java (or in @Configuration classes), for example:

@Bean
public StatefulRetryOperationsInterceptor interceptor() {
	return RetryInterceptorBuilder.stateful()
			.maxAttempts(5)
			.backOffOptions(1000, 2.0, 10000) // initialInterval, multiplier, maxInterval
			.build();
}

Only a subset of retry capabilities can be configured this way; more advanced features would need the configuration of a RetryTemplate as a Spring bean. See the Spring Retry Javadocs for complete information about available policies and their configuration.

Message Listeners and the Asynchronous Case

If a MessageListener fails because of a business exception, the exception is handled by the message listener container and then it goes back to listening for another message. If the failure is caused by a dropped connection (not a business exception), then the consumer that is collecting messages for the listener has to be cancelled and restarted. The SimpleMessageListenerContainer handles this seamlessly, and it leaves a log to say that the listener is being restarted. In fact it loops endlessly trying to restart the consumer, and only if the consumer is very badly behaved indeed will it give up. One side effect is that if the broker is down when the container starts, it will just keep trying until a connection can be established.

Business exception handling, as opposed to protocol errors and dropped connections, might need more thought and some custom configuration, especially if transactions and/or container acks are in use. Prior to 2.8.x, RabbitMQ had no definition of dead letter behaviour, so by default a message that is rejected or rolled back because of a business exception can be redelivered ad infinitum. To put a limit in the client on the number of re-deliveries, one choice is a StatefulRetryOperationsInterceptor in the advice chain of the listener. The interceptor can have a recovery callback that implements a custom dead letter action: whatever is appropriate for your particular environment.

Another alternative is to set the container’s defaultRequeueRejected property to false. This causes all failed messages to be discarded. When using RabbitMQ 2.8.x or higher, this also facilitates delivering the message to a Dead Letter Exchange.

Or, you can throw a AmqpRejectAndDontRequeueException; this prevents message requeuing, regardless of the setting of the defaultRequeueRejected property.

Often, a combination of both techniques will be used. Use a StatefulRetryOperationsInterceptor in the advice chain, with a MessageRecoverer that throws an AmqpRejectAndDontRequeueException. The MessageRecover is called when all retries have been exhausted. The RejectAndDontRequeueRecoverer does exactly that. The default MessageRecoverer simply consumes the errant message and emits a WARN message.

Starting with version 1.3, a new RepublishMessageRecoverer is provided, to allow publishing of failed messages after retries are exhausted:

When a recoverer consumes the final exception, the message is ACK’d and won’t be sent to the Dead Letter Exchange, if any.

[Note]Note

When RepublishMessageRecoverer is used on the consumer side, the received message has deliveryMode in the receivedDeliveryMode message property, the deliveryMode is this case is null. That means a NON_PERSISTENT delivery mode on the Broker. Starting with version 2.0, the RepublishMessageRecoverer can be configured for the deliveryMode to set into the message to republish if it is null. By default it uses MessageProperties default value - MessageDeliveryMode.PERSISTENT.

@Bean
RetryOperationsInterceptor interceptor() {
	return RetryInterceptorBuilder.stateless()
			.maxAttempts(5)
			.recoverer(new RepublishMessageRecoverer(amqpTemplate(), "bar", "baz"))
			.build();
}

The RepublishMessageRecoverer publishes the message with additional information in message headers, such as the exception message, stack trace, original exchange and routing key. Additional headers can be added by creating a subclass and overriding additionalHeaders(). The deliveryMode (or any other properties) can be changed in the additionalHeaders(), too:

RepublishMessageRecoverer recoverer = new RepublishMessageRecoverer(amqpTemplate, "error") {

    protected Map<? extends String, ? extends Object> additionalHeaders(Message message, Throwable cause) {
        message.getMessageProperties().setDeliveryMode(message.getMessageProperties().getReceivedDeliveryMode());
        return null;
    }

};

Exception Classification for Retry

Spring Retry has a great deal of flexibility for determining which exceptions can invoke retry. The default configuration will retry for all exceptions. Given that user exceptions will be wrapped in a ListenerExecutionFailedException we need to ensure that the classification examines the exception causes. The default classifier just looks at the top level exception.

Since Spring Retry 1.0.3, the BinaryExceptionClassifier has a property traverseCauses (default false). When true it will traverse exception causes until it finds a match or there is no cause.

To use this classifier for retry, use a SimpleRetryPolicy created with the constructor that takes the max attempts, the Map of Exception s and the boolean (traverseCauses), and inject this policy into the RetryTemplate.

3.1.20 Debugging

Spring AMQP provides extensive logging, especially at DEBUG level.

If you wish to monitor the AMQP protocol between the application and broker, you could use a tool such as WireShark, which has a plugin to decode the protocol. Alternatively the RabbitMQ java client comes with a very useful class Tracer. When run as a main, by default, it listens on port 5673 and connects to port 5672 on localhost. Simply run it, and change your connection factory configuration to connect to port 5673 on localhost. It displays the decoded protocol on the console. Refer to the Tracer javadocs for more information.

3.2 Logging Subsystem AMQP Appenders

The framework provides logging appenders for several popular logging subsystems:

  • logback (since Spring AMQP version 1.4)
  • log4j2 (since Spring AMQP version 1.6)

The appenders are configured using the normal mechanisms for the logging subsystem, available properties are specified in the following sections.

3.2.1 Common properties

The following properties are available with all appenders:

Table 3.4. Common Appender Properties

PropertyDefaultDescription
exchangeName
logs

Name of the exchange to publish log events to.

exchangeType
topic

Type of the exchange to publish log events to - only needed if the appender declares the exchange. See declareExchange.

routingKeyPattern
%c.%p

Logging subsystem pattern format to use to generate a routing key.

applicationId

Application ID - added to the routing key if the pattern includes %X{applicationId}.

senderPoolSize
2

The number of threads to use to publish log events.

maxSenderRetries
30

How many times to retry sending a message if the broker is unavailable or there is some other error. Retries are delayed like: N ^ log(N), where N is the retry number.

addresses

A comma-delimited list of broker addresses: host:port[,host:port]* - overrides host and port.

host
localhost

RabbitMQ host to connect to.

port
5672

RabbitMQ port to connect to.

virtualHost
/

RabbitMQ virtual host to connect to.

username
guest

RabbitMQ user to connect as.

password
guest

RabbitMQ password for this user.

useSsl
false

Use SSL for the RabbitMQ connection. See the section called “RabbitConnectionFactoryBean and Configuring SSL”

sslAlgorithm
null

The SSL algorithm to use.

sslPropertiesLocation
null

Location of the SSL properties file.

keyStore
null

Location of the keystore.

keyStorePassphrase
null

Passphrase for the keystore.

keyStoreType
JKS

The keystore type.

trustStore
null

Location of the truststore.

trustStorePassphrase
null

Passphrase for the truststore.

trustStoreType
JKS

The truststore type.

contentType
text/plain

content-type property of log messages.

contentEncoding

content-encoding property of log messages.

declareExchange
false

Whether or not to declare the configured exchange when this appender starts. Also see durable and autoDelete.

durable
true

When declareExchange is true the durable flag is set to this value.

autoDelete
false

When declareExchange is true the auto delete flag is set to this value.

charset
null

Charset to use when converting String to byte[], default null (system default charset used). If the charset is unsupported on the current platform, we fall back to using the system charset.

deliveryMode
PERSISTENT

PERSISTENT or NON_PERSISTENT to determine whether or not RabbitMQ should persist the messages.

generateId
false

Used to determine whether the messageId property is set to a unique value.

clientConnection
Properties
null

A comma-delimited list of key:value pairs for custom client properties to the RabbitMQ connection.


3.2.2 Log4j2 Appender

Example log4j2.xml Snippet. 

<Appenders>
    ...
    <RabbitMQ name="rabbitmq"
        addresses="foo:5672,bar:5672" user="guest" password="guest" virtualHost="/"
        exchange="log4j2" exchangeType="topic" declareExchange="true" durable="true" autoDelete="false"
        applicationId="myAppId" routingKeyPattern="%X{applicationId}.%c.%p"
        contentType="text/plain" contentEncoding="UTF-8" generateId="true" deliveryMode="NON_PERSISTENT"
        charset="UTF-8"
        senderPoolSize="3" maxSenderRetries="5">
    </RabbitMQ>
</Appenders>

[Important]Important

Starting with versions 1.6.10, 1.7.3, the log4j2 Appender publishes the messages to RabbitMQ on the calling thread by default. This is because log4j2 does not create thread-safe events by default. If the broker is down, the maxSenderRetries will be used to retry, with no delay between retries. If you wish to restore the previous behavior of publishing the messages on separate threads (senderPoolSize), set the async property to true. However, you will also need to configure log4j2 to use the DefaultLogEventFactory instead of the ReusableLogEventFactory. One way to do that is to set the system property -Dlog4j2.enable.threadlocals=false. If async publishing is used with the ReusableLogEventFactory, events will have a high likelihood of being corrupted due to cross-talk.

3.2.3 Logback Appender

Example logback.xml Snippet. 

<appender name="AMQP" class="org.springframework.amqp.rabbit.logback.AmqpAppender">
    <layout>
        <pattern><![CDATA[ %d %p %t [%c] - <%m>%n ]]></pattern>
    </layout>
    <addresses>foo:5672,bar:5672</addresses>
    <abbreviation>36</abbreviation>
    <includeCallerData>false</includeCallerData>
    <applicationId>myApplication</applicationId>
    <routingKeyPattern>%property{applicationId}.%c.%p</routingKeyPattern>
    <generateId>true</generateId>
    <charset>UTF-8</charset>
    <durable>false</durable>
    <deliveryMode>NON_PERSISTENT</deliveryMode>
    <declareExchange>true</declareExchange>
</appender>

Starting with version 1.7.1, the Logback AmqpAppender provides an includeCallerData option which is false by default. Extracting caller data can be rather expensive because the log event has to create a throwable and inspect it to determine the calling location. Therefore, by default, caller data associated with an event is not extracted when the event added to the event queue. You can configure the appender to include caller data by setting the includeCallerData property to true.

Starting with version 2.0.0, the Logback AmqpAppender supports Logback encoders with the encoder option. The encoder and layout options are mutually exclusive.

3.2.4 Customizing the Messages

By default AMQP appenders populates these message properties: * deliveryMode * contentType * contentEncoding if configured * messageId if generateId is configured * timestamp of the log event * appId if applicationId is configured

In addition they populate headers: * categoryName of the log event * level of the log event * thread the name of the thread where log event happened * location the stack trace of the log event call * copy of all the MDC properties

Each of the appenders can be subclassed, allowing you to modify the messages before publishing.

Customizing the Log Messages. 

public class MyEnhancedAppender extends AmqpAppender {

    @Override
    public Message postProcessMessageBeforeSend(Message message, Event event) {
        message.getMessageProperties().setHeader("foo", "bar");
        return message;
    }

}

3.2.5 Customizing the Client Properties

Simple String Properties

Each appender supports adding client properties to the RabbitMQ connection.

logback. 

<appender name="AMQP" ...>
    ...
    <clientConnectionProperties>foo:bar,baz:qux</clientConnectionProperties>
    ...
</appender>

log4j2. 

<Appenders>
    ...
    <RabbitMQ name="rabbitmq"
        ...
        clientConnectionProperties="foo:bar,baz:qux"
        ...
    </RabbitMQ>
</Appenders>

The properties are a comma-delimited list of key:value pairs; keys and values cannot contain commas or colons.

These properties appear on the RabbitMQ Admin UI when viewing the connection.

Advanced Technique for Logback

The Logback appender can be subclassed, allowing you to modify the client connection properties before the connection is established:

Customizing the Client Connection Properties. 

public class MyEnhancedAppender extends AmqpAppender {

    private String foo;

    @Override
    protected void updateConnectionClientProperties(Map<String, Object> clientProperties) {
        clientProperties.put("foo", this.foo);
    }

    public void setFoo(String foo) {
        this.foo = foo;
    }

}

Then add <foo>bar</foo> to logback.xml.

Of course, for simple String properties like this example, the previous technique can be used; subclasses allow richer properties (such as adding a Map or numeric property).

With log4j2, subclasses are not supported, due to the way log4j2 uses static factory methods.

3.3 Sample Applications

3.3.1 Introduction

The Spring AMQP Samples project includes two sample applications. The first is a simple "Hello World" example that demonstrates both synchronous and asynchronous message reception. It provides an excellent starting point for acquiring an understanding of the essential components. The second sample is based on a stock-trading use case to demonstrate the types of interaction that would be common in real world applications. In this chapter, we will provide a quick walk-through of each sample so that you can focus on the most important components. The samples are both Maven-based, so you should be able to import them directly into any Maven-aware IDE (such as SpringSource Tool Suite).

3.3.2 Hello World

Introduction

The Hello World sample demonstrates both synchronous and asynchronous message reception. You can import the spring-rabbit-helloworld sample into the IDE and then follow the discussion below.

Synchronous Example

Within the src/main/java directory, navigate to the org.springframework.amqp.helloworld package. Open the HelloWorldConfiguration class and notice that it contains the @Configuration annotation at class-level and some @Bean annotations at method-level. This is an example of Spring’s Java-based configuration. You can read more about thathttp://docs.spring.io/spring/docs/current/spring-framework-reference/html/beans.html#beans-java[here].

@Bean
public ConnectionFactory connectionFactory() {
    CachingConnectionFactory connectionFactory =
        new CachingConnectionFactory("localhost");
    connectionFactory.setUsername("guest");
    connectionFactory.setPassword("guest");
    return connectionFactory;
}

The configuration also contains an instance of RabbitAdmin, which by default looks for any beans of type Exchange, Queue, or Binding and then declares them on the broker. In fact, the "helloWorldQueue" bean that is generated in HelloWorldConfiguration is an example simply because it is an instance of Queue.

@Bean
public Queue helloWorldQueue() {
    return new Queue(this.helloWorldQueueName);
}

Looking back at the "rabbitTemplate" bean configuration, you will see that it has the helloWorldQueue’s name set as its "queue" property (for receiving Messages) and for its "routingKey" property (for sending Messages).

Now that we’ve explored the configuration, let’s look at the code that actually uses these components. First, open the Producer class from within the same package. It contains a main() method where the Spring ApplicationContext is created.

public static void main(String[] args) {
    ApplicationContext context =
        new AnnotationConfigApplicationContext(RabbitConfiguration.class);
    AmqpTemplate amqpTemplate = context.getBean(AmqpTemplate.class);
    amqpTemplate.convertAndSend("Hello World");
    System.out.println("Sent: Hello World");
}

As you can see in the example above, the AmqpTemplate bean is retrieved and used for sending a Message. Since the client code should rely on interfaces whenever possible, the type is AmqpTemplate rather than RabbitTemplate. Even though the bean created in HelloWorldConfiguration is an instance of RabbitTemplate, relying on the interface means that this code is more portable (the configuration can be changed independently of the code). Since the convertAndSend() method is invoked, the template will be delegating to its MessageConverter instance. In this case, it’s using the default SimpleMessageConverter, but a different implementation could be provided to the "rabbitTemplate" bean as defined in HelloWorldConfiguration.

Now open the Consumer class. It actually shares the same configuration base class which means it will be sharing the "rabbitTemplate" bean. That’s why we configured that template with both a "routingKey" (for sending) and "queue" (for receiving). As you saw in Section 3.1.4, “AmqpTemplate”, you could instead pass the routingKey argument to the send method and the queue argument to the receive method. The Consumer code is basically a mirror image of the Producer, calling receiveAndConvert() rather than convertAndSend().

public static void main(String[] args) {
    ApplicationContext context =
        new AnnotationConfigApplicationContext(RabbitConfiguration.class);
    AmqpTemplate amqpTemplate = context.getBean(AmqpTemplate.class);
    System.out.println("Received: " + amqpTemplate.receiveAndConvert());
}

If you run the Producer, and then run the Consumer, you should see the message "Received: Hello World" in the console output.

Asynchronous Example

Now that we’ve walked through the synchronous Hello World sample, it’s time to move on to a slightly more advanced but significantly more powerful option. With a few modifications, the Hello World sample can provide an example of asynchronous reception, a.k.a. Message-driven POJOs. In fact, there is a sub-package that provides exactly that: org.springframework.amqp.samples.helloworld.async.

Once again, we will start with the sending side. Open the ProducerConfiguration class and notice that it creates a "connectionFactory" and "rabbitTemplate" bean. This time, since the configuration is dedicated to the message sending side, we don’t even need any Queue definitions, and the RabbitTemplate only has the routingKey property set. Recall that messages are sent to an Exchange rather than being sent directly to a Queue. The AMQP default Exchange is a direct Exchange with no name. All Queues are bound to that default Exchange with their name as the routing key. That is why we only need to provide the routing key here.

public RabbitTemplate rabbitTemplate() {
    RabbitTemplate template = new RabbitTemplate(connectionFactory());
    template.setRoutingKey(this.helloWorldQueueName);
    return template;
}

Since this sample will be demonstrating asynchronous message reception, the producing side is designed to continuously send messages (if it were a message-per-execution model like the synchronous version, it would not be quite so obvious that it is in fact a message-driven consumer). The component responsible for sending messages continuously is defined as an inner class within the ProducerConfiguration. It is configured to execute every 3 seconds.

static class ScheduledProducer {

    @Autowired
    private volatile RabbitTemplate rabbitTemplate;

    private final AtomicInteger counter = new AtomicInteger();

    @Scheduled(fixedRate = 3000)
    public void sendMessage() {
        rabbitTemplate.convertAndSend("Hello World " + counter.incrementAndGet());
    }
}

You don’t need to understand all of the details since the real focus should be on the receiving side (which we will cover momentarily). However, if you are not yet familiar with Spring task scheduling support, you can learn more here. The short story is that the "postProcessor" bean in the ProducerConfiguration is registering the task with a scheduler.

Now, let’s turn to the receiving side. To emphasize the Message-driven POJO behavior will start with the component that is reacting to the messages. The class is called HelloWorldHandler.

public class HelloWorldHandler {

    public void handleMessage(String text) {
        System.out.println("Received: " + text);
    }

}

Clearly, that is a POJO. It does not extend any base class, it doesn’t implement any interfaces, and it doesn’t even contain any imports. It is being "adapted" to the MessageListener interface by the Spring AMQP MessageListenerAdapter. That adapter can then be configured on a SimpleMessageListenerContainer. For this sample, the container is created in the ConsumerConfiguration class. You can see the POJO wrapped in the adapter there.

@Bean
public SimpleMessageListenerContainer listenerContainer() {
    SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();
    container.setConnectionFactory(connectionFactory());
    container.setQueueName(this.helloWorldQueueName);
    container.setMessageListener(new MessageListenerAdapter(new HelloWorldHandler()));
    return container;
}

The SimpleMessageListenerContainer is a Spring lifecycle component and will start automatically by default. If you look in the Consumer class, you will see that its main() method consists of nothing more than a one-line bootstrap to create the ApplicationContext. The Producer’s main() method is also a one-line bootstrap, since the component whose method is annotated with @Scheduled will also start executing automatically. You can start the Producer and Consumer in any order, and you should see messages being sent and received every 3 seconds.

3.3.3 Stock Trading

The Stock Trading sample demonstrates more advanced messaging scenarios than the Hello World sample. However, the configuration is very similar - just a bit more involved. Since we’ve walked through the Hello World configuration in detail, here we’ll focus on what makes this sample different. There is a server that pushes market data (stock quotes) to a Topic Exchange. Then, clients can subscribe to the market data feed by binding a Queue with a routing pattern (e.g. app.stock.quotes.nasdaq.*). The other main feature of this demo is a request-reply "stock trade" interaction that is initiated by the client and handled by the server. That involves a private "replyTo" Queue that is sent by the client within the order request Message itself.

The Server’s core configuration is in the RabbitServerConfiguration class within the org.springframework.amqp.rabbit.stocks.config.server package. It extends the AbstractStockAppRabbitConfiguration. That is where the resources common to the Server and Client(s) are defined, including the market data Topic Exchange (whose name is app.stock.marketdata) and the Queue that the Server exposes for stock trades (whose name is app.stock.request). In that common configuration file, you will also see that a Jackson2JsonMessageConverter is configured on the RabbitTemplate.

The Server-specific configuration consists of 2 things. First, it configures the market data exchange on the RabbitTemplate so that it does not need to provide that exchange name with every call to send a Message. It does this within an abstract callback method defined in the base configuration class.

public void configureRabbitTemplate(RabbitTemplate rabbitTemplate) {
    rabbitTemplate.setExchange(MARKET_DATA_EXCHANGE_NAME);
}

Secondly, the stock request queue is declared. It does not require any explicit bindings in this case, because it will be bound to the default no-name exchange with its own name as the routing key. As mentioned earlier, the AMQP specification defines that behavior.

@Bean
public Queue stockRequestQueue() {
    return new Queue(STOCK_REQUEST_QUEUE_NAME);
}

Now that you’ve seen the configuration of the Server’s AMQP resources, navigate to the org.springframework.amqp.rabbit.stocks package under the src/test/java directory. There you will see the actual Server class that provides a main() method. It creates an ApplicationContext based on the server-bootstrap.xml config file. In there you will see the scheduled task that publishes dummy market data. That configuration relies upon Spring’s "task" namespace support. The bootstrap config file also imports a few other files. The most interesting one is server-messaging.xml which is directly under src/main/resources. In there you will see the "messageListenerContainer" bean that is responsible for handling the stock trade requests. Finally have a look at the "serverHandler" bean that is defined in "server-handlers.xml" (also in src/main/resources). That bean is an instance of the ServerHandler class and is a good example of a Message-driven POJO that is also capable of sending reply Messages. Notice that it is not itself coupled to the framework or any of the AMQP concepts. It simply accepts a TradeRequest and returns a TradeResponse.

public TradeResponse handleMessage(TradeRequest tradeRequest) { ...
}

Now that we’ve seen the most important configuration and code for the Server, let’s turn to the Client. The best starting point is probably RabbitClientConfiguration within the org.springframework.amqp.rabbit.stocks.config.client package. Notice that it declares two queues without providing explicit names.

@Bean
public Queue marketDataQueue() {
    return amqpAdmin().declareQueue();
}

@Bean
public Queue traderJoeQueue() {
    return amqpAdmin().declareQueue();
}

Those are private queues, and unique names will be generated automatically. The first generated queue is used by the Client to bind to the market data exchange that has been exposed by the Server. Recall that in AMQP, consumers interact with Queues while producers interact with Exchanges. The "binding" of Queues to Exchanges is what instructs the broker to deliver, or route, messages from a given Exchange to a Queue. Since the market data exchange is a Topic Exchange, the binding can be expressed with a routing pattern. The RabbitClientConfiguration declares that with a Binding object, and that object is generated with the BindingBuilder fluent API.

@Value("${stocks.quote.pattern}")
private String marketDataRoutingKey;

@Bean
public Binding marketDataBinding() {
    return BindingBuilder.bind(
        marketDataQueue()).to(marketDataExchange()).with(marketDataRoutingKey);
}

Notice that the actual value has been externalized in a properties file ("client.properties" under src/main/resources), and that we are using Spring’s @Value annotation to inject that value. This is generally a good idea, since otherwise the value would have been hardcoded in a class and unmodifiable without recompilation. In this case, it makes it much easier to run multiple versions of the Client while making changes to the routing pattern used for binding. Let’s try that now.

Start by running org.springframework.amqp.rabbit.stocks.Server and then org.springframework.amqp.rabbit.stocks.Client. You should see dummy quotes for NASDAQ stocks because the current value associated with the stocks.quote.pattern key in client.properties is app.stock.quotes.nasdaq.. Now, while keeping the existing Server and Client running, change that property value to app.stock.quotes.nyse. and start a second Client instance. You should see that the first client is still receiving NASDAQ quotes while the second client receives NYSE quotes. You could instead change the pattern to get all stocks or even an individual ticker.

The final feature we’ll explore is the request-reply interaction from the Client’s perspective. Recall that we have already seen the ServerHandler that is accepting TradeRequest objects and returning TradeResponse objects. The corresponding code on the Client side is RabbitStockServiceGateway in the org.springframework.amqp.rabbit.stocks.gateway package. It delegates to the RabbitTemplate in order to send Messages.

public void send(TradeRequest tradeRequest) {
    getRabbitTemplate().convertAndSend(tradeRequest, new MessagePostProcessor() {
        public Message postProcessMessage(Message message) throws AmqpException {
            message.getMessageProperties().setReplyTo(new Address(defaultReplyToQueue));
            try {
                message.getMessageProperties().setCorrelationId(
                    UUID.randomUUID().toString().getBytes("UTF-8"));
            }
            catch (UnsupportedEncodingException e) {
                throw new AmqpException(e);
            }
            return message;
        }
    });
}

Notice that prior to sending the message, it sets the "replyTo" address. It’s providing the queue that was generated by the "traderJoeQueue" bean definition shown above. Here’s the @Bean definition for the StockServiceGateway class itself.

@Bean
public StockServiceGateway stockServiceGateway() {
    RabbitStockServiceGateway gateway = new RabbitStockServiceGateway();
    gateway.setRabbitTemplate(rabbitTemplate());
    gateway.setDefaultReplyToQueue(traderJoeQueue());
    return gateway;
}

If you are no longer running the Server and Client, start them now. Try sending a request with the format of 100 TCKR. After a brief artificial delay that simulates "processing" of the request, you should see a confirmation message appear on the Client.

3.3.4 Receiving JSON from Non-Spring Applications

Spring applications, when sending JSON, set the __TypeId__ header to the fully qualified class name to assist the receiving application in converting the JSON back to a Java object.

The spring-rabbit-json sample explores several techniques to convert the JSON from a non-Spring application.

See also the section called “Jackson2JsonMessageConverter” as well as the Javadoc for the DefaultClassMapper.

3.4 Testing Support

3.4.1 Introduction

Writing integration for asynchronous applications is necessarily more complex than testing simpler applications. This is made more complex when abstractions such as the @RabbitListener annotations come into the picture. The question being how to verify that, after sending a message, the listener received the message as expected.

The framework itself has many unit and integration tests; some using mocks, others using integration testing with a live RabbitMQ broker. You can consult those tests for some ideas for testing scenarios.

Spring AMQP version 1.6 introduced the spring-rabbit-test jar which provides support for testing some of these more complex scenarios. It is anticipated that this project will expand over time but we need community feedback to make suggestions for features needed to help with testing. Please use JIRA or GitHub Issues to provide such feedback.

3.4.2 Mockito Answer<?> Implementations

There are currently two Answer<?> implementations to help with testing:

The first, LatchCountDownAndCallRealMethodAnswer provides an Answer<Void> that returns null and counts down a latch.

LatchCountDownAndCallRealMethodAnswer answer = new LatchCountDownAndCallRealMethodAnswer(2);
doAnswer(answer)
    .when(listener).foo(anyString(), anyString());

...

assertTrue(answer.getLatch().await(10, TimeUnit.SECONDS));

The second, LambdaAnswer<T> provides a mechanism to optionally call the real method and provides an opportunity to return a custom result, based on the InvocationOnMock and the result (if any).

public class Foo {

    public String foo(String foo) {
        return foo.toUpperCase();
    }

}
Foo foo = spy(new Foo());

doAnswer(new LambdaAnswer<String>(true, (i, r) -> r + r))
    .when(foo).foo(anyString());
assertEquals("FOOFOO", foo.foo("foo"));

doAnswer(new LambdaAnswer<String>(true, (i, r) -> r + i.getArguments()[0]))
    .when(foo).foo(anyString());
assertEquals("FOOfoo", foo.foo("foo"));

doAnswer(new LambdaAnswer<String>(false, (i, r) ->
    "" + i.getArguments()[0] + i.getArguments()[0])).when(foo).foo(anyString());
assertEquals("foofoo", foo.foo("foo"));

When using Java 7 or earlier:

doAnswer(new LambdaAnswer<String>(true, new ValueToReturn<String>() {
    @Override
    public String apply(InvocationOnMock i, String r) {
        return r + r;
    }
})).when(foo).foo(anyString());

3.4.3 @RabbitListenerTest and RabbitListenerTestHarness

Annotating one of your @Configuration classes with @RabbitListenerTest will cause the framework to replace the standard RabbitListenerAnnotationBeanPostProcessor with a subclass RabbitListenerTestHarness (it will also enable @RabbitListener detection via @EnableRabbit).

The RabbitListenerTestHarness enhances the listener in two ways - it wraps it in a Mockito Spy, enabling normal Mockito stubbing and verification operations. It can also add an Advice to the listener enabling access to the arguments, result and or exceptions thrown. You can control which (or both) of these are enabled with attributes on the @RabbitListenerTest. The latter is provided for access to lower-level data about the invocation - it also supports blocking the test thread until the async listener is called.

[Important]Important

final @RabbitListener methods cannot be spied or advised; also, only listeners with an id attribute can be spied or advised.

Let’s take a look at some examples.

Using spy:

@Configuration
@RabbitListenerTest
public class Config {

    @Bean
    public Listener listener() {
        return new Listener();
    }

    ...

}

public class Listener {

    @RabbitListener(id="foo", queues="#{queue1.name}")
    public String foo(String foo) {
        return foo.toUpperCase();
    }

    @RabbitListener(id="bar", queues="#{queue2.name}")
    public void foo(@Payload String foo, @Header("amqp_receivedRoutingKey") String rk) {
        ...
    }

}

public class MyTests {

    @Autowired
    private RabbitListenerTestHarness harness; 1

    @Test
    public void testTwoWay() throws Exception {
        assertEquals("FOO", this.rabbitTemplate.convertSendAndReceive(this.queue1.getName(), "foo"));

        Listener listener = this.harness.getSpy("foo"); 2
        assertNotNull(listener);
        verify(listener).foo("foo");
    }

    @Test
    public void testOneWay() throws Exception {
        Listener listener = this.harness.getSpy("bar");
        assertNotNull(listener);

        LatchCountDownAndCallRealMethodAnswer answer = new LatchCountDownAndCallRealMethodAnswer(2); 3
        doAnswer(answer).when(listener).foo(anyString(), anyString()); 4

        this.rabbitTemplate.convertAndSend(this.queue2.getName(), "bar");
        this.rabbitTemplate.convertAndSend(this.queue2.getName(), "baz");

        assertTrue(answer.getLatch().await(10, TimeUnit.SECONDS));
        verify(listener).foo("bar", this.queue2.getName());
        verify(listener).foo("baz", this.queue2.getName());
    }

}

1

Inject the harness into the test case so we can get access to the spy.

2

Get a reference to the spy so we can verify it was invoked as expected. Since this is a send and receive operation, there is no need to suspend the test thread because it was already suspended in the RabbitTemplate waiting for the reply.

3

In this case, we’re only using a send operation so we need a latch to wait for the asynchronous call to the listener on the container thread. We use one of the Answer<?> implementations to help with that.

4

Configure the spy to invoke the Answer.

Using the capture advice:

@Configuration
@ComponentScan
@RabbitListenerTest(spy = false, capture = true)
public class Config {

}

@Service
public class Listener {

    private boolean failed;

    @RabbitListener(id="foo", queues="#{queue1.name}")
    public String foo(String foo) {
        return foo.toUpperCase();
    }

    @RabbitListener(id="bar", queues="#{queue2.name}")
    public void foo(@Payload String foo, @Header("amqp_receivedRoutingKey") String rk) {
        if (!failed && foo.equals("ex")) {
            failed = true;
            throw new RuntimeException(foo);
        }
        failed = false;
    }

}

public class MyTests {

    @Autowired
    private RabbitListenerTestHarness harness; 1

    @Test
    public void testTwoWay() throws Exception {
        assertEquals("FOO", this.rabbitTemplate.convertSendAndReceive(this.queue1.getName(), "foo"));

        InvocationData invocationData =
            this.harness.getNextInvocationDataFor("foo", 0, TimeUnit.SECONDS); 2
        assertThat(invocationData.getArguments()[0], equalTo("foo"));     3
        assertThat((String) invocationData.getResult(), equalTo("FOO"));
    }

    @Test
    public void testOneWay() throws Exception {
        this.rabbitTemplate.convertAndSend(this.queue2.getName(), "bar");
        this.rabbitTemplate.convertAndSend(this.queue2.getName(), "baz");
        this.rabbitTemplate.convertAndSend(this.queue2.getName(), "ex");

        InvocationData invocationData =
            this.harness.getNextInvocationDataFor("bar", 10, TimeUnit.SECONDS); 4
        Object[] args = invocationData.getArguments();
        assertThat((String) args[0], equalTo("bar"));
        assertThat((String) args[1], equalTo(queue2.getName()));

        invocationData = this.harness.getNextInvocationDataFor("bar", 10, TimeUnit.SECONDS);
        args = invocationData.getArguments();
        assertThat((String) args[0], equalTo("baz"));

        invocationData = this.harness.getNextInvocationDataFor("bar", 10, TimeUnit.SECONDS);
        args = invocationData.getArguments();
        assertThat((String) args[0], equalTo("ex"));
        assertEquals("ex", invocationData.getThrowable().getMessage()); 5
    }

}

1

Inject the harness into the test case so we can get access to the spy.

2

Use harness.getNextInvocationDataFor() to retrieve the invocation data - in this case since it was a request/reply scenario there is no need to wait for any time because the test thread was suspended in the RabbitTemplate waiting for the result.

3

We can then verify that the argument and result was as expected.

4

This time we need some time to wait for the data, since it’s an async operation on the container thread and we need to suspend the test thread.

5

When the listener throws an exception, it is available in the throwable property of the invocation data.

3.4.4 TestRabbitTemplate

The TestRabbitTemplate is provided to perform some basic integration testing without the need for a broker. When adding it as @Bean in your test case, it discovers all the listener containers in the context, either declared as @Bean, <bean/>`s or using the `@RabbitListener annotation. It currently only supports routing by queue name. The template extracts the message listener from the container, and invokes it directly on the test thread. Request/Reply messaging (sendAndReceive methods) is supported for listeners that return replies.

Here is a simple test case that uses the template:

@RunWith(SpringRunner.class)
public class TestRabbitTemplateTests {

	@Autowired
	private TestRabbitTemplate template;

	@Autowired
	private Config config;

	@Test
	public void testSimpleSends() {
		this.template.convertAndSend("foo", "hello1");
		assertThat(this.config.fooIn, equalTo("foo:hello1"));
		this.template.convertAndSend("bar", "hello2");
		assertThat(this.config.barIn, equalTo("bar:hello2"));
		assertThat(this.config.smlc1In, equalTo("smlc1:"));
		this.template.convertAndSend("foo", "hello3");
		assertThat(this.config.fooIn, equalTo("foo:hello1"));
		this.template.convertAndSend("bar", "hello4");
		assertThat(this.config.barIn, equalTo("bar:hello2"));
		assertThat(this.config.smlc1In, equalTo("smlc1:hello3hello4"));

		this.template.setBroadcast(true);
		this.template.convertAndSend("foo", "hello5");
		assertThat(this.config.fooIn, equalTo("foo:hello1foo:hello5"));
		this.template.convertAndSend("bar", "hello6");
		assertThat(this.config.barIn, equalTo("bar:hello2bar:hello6"));
		assertThat(this.config.smlc1In, equalTo("smlc1:hello3hello4hello5hello6"));
	}

	@Test
	public void testSendAndReceive() {
		assertThat(this.template.convertSendAndReceive("baz", "hello"), equalTo("baz:hello"));
	}
	@Configuration
	@EnableRabbit
	public static class Config {

		public String fooIn = "";

		public String barIn = "";

		public String smlc1In = "smlc1:";

		@Bean
		public TestRabbitTemplate template() throws IOException {
			return new TestRabbitTemplate(connectionFactory());
		}

		@Bean
		public ConnectionFactory connectionFactory() throws IOException {
			ConnectionFactory factory = mock(ConnectionFactory.class);
			Connection connection = mock(Connection.class);
			Channel channel = mock(Channel.class);
			willReturn(connection).given(factory).createConnection();
			willReturn(channel).given(connection).createChannel(anyBoolean());
			given(channel.isOpen()).willReturn(true);
			return factory;
		}

		@Bean
		public SimpleRabbitListenerContainerFactory rabbitListenerContainerFactory() throws IOException {
			SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
			factory.setConnectionFactory(connectionFactory());
			return factory;
		}

		@RabbitListener(queues = "foo")
		public void foo(String in) {
			this.fooIn += "foo:" + in;
		}

		@RabbitListener(queues = "bar")
		public void bar(String in) {
			this.barIn += "bar:" + in;
		}

		@RabbitListener(queues = "baz")
		public String baz(String in) {
			return "baz:" + in;
		}

		@Bean
		public SimpleMessageListenerContainer smlc1() throws IOException {
			SimpleMessageListenerContainer container = new SimpleMessageListenerContainer(connectionFactory());
			container.setQueueNames("foo", "bar");
			container.setMessageListener(new MessageListenerAdapter(new Object() {

				@SuppressWarnings("unused")
				public void handleMessage(String in) {
					smlc1In += in;
				}

			}));
			return container;
		}

	}

}

3.4.5 JUnit @Rules

Spring AMQP version 1.7 provides an additional jar spring-rabbit-junit; this jar contains a couple of utility @Rule s for use when running JUnit tests.

BrokerRunning

BrokerRunning provides a mechanism to allow tests to succeed when a broker is not running (on localhost, by default).

It also has utility methods to initialize/empty queues, and delete queues and exchanges.

Usage:

@ClassRule
public static BrokerRunning brokerRunning = BrokerRunning.isRunningWithEmptyQueues("foo", "bar");

@AfterClass
public static void tearDown() {
    brokerRunning.removeTestQueues("some.other.queue.too") // removes foo, bar as well
}

There are several isRunning... static methods such as isBrokerAndManagementRunning() which verifies the broker has the management plugin enabled.

Configuring the Rule

There are times when you want tests to fail if there is no broker, such as a nightly CI build. To disable the rule at runtime, set an environment variable RABBITMQ_SERVER_REQUIRED to true.

You can override the broker properties, such as hostname in several ways:

  • Setters
@ClassRule
public static BrokerRunning brokerRunning = BrokerRunning.isRunningWithEmptyQueues("foo", "bar");

static {
    brokerRunning.setHostName("10.0.0.1")
}

@AfterClass
public static void tearDown() {
    brokerRunning.removeTestQueues("some.other.queue.too") // removes foo, bar as well
}
  • Environment Variables

The following environment variables are provided:

public static final String BROKER_ADMIN_URI = "RABBITMQ_TEST_ADMIN_URI";
public static final String BROKER_HOSTNAME = "RABBITMQ_TEST_HOSTNAME";
public static final String BROKER_PORT = "RABBITMQ_TEST_PORT";
public static final String BROKER_USER = "RABBITMQ_TEST_USER";
public static final String BROKER_PW = "RABBITMQ_TEST_PASSWORD";
public static final String BROKER_ADMIN_USER = "RABBITMQ_TEST_ADMIN_USER";
public static final String BROKER_ADMIN_PW = "RABBITMQ_TEST_ADMIN_PASSWORD";

These will override the default settings (localhost:5672 for amqp and http://localhost:15672/api/ for the management REST API).

Changing the host name affects both the amqp and management REST API connection (unless the admin uri is explicitly set).

BrokerRunning also provides a static method: setEnvironmentVariableOverrides where you can pass in a map containing these variables; they override system environment variables. This might be useful if you wish to use different configuration for tests in multiple test suites. IMPORTANT: The method must be called before invoking any of the isRunning() static methods that create the rule instance. Variable values will be applied to all instances created after this. Invoke clearEnvironmentVariableOverrides() to reset the rule to use defaults (including any actual environment variables).

In your test cases, you can use those properties when creating the connection factory:

@Bean
public ConnectionFactory rabbitConnectionFactory() {
    CachingConnectionFactory connectionFactory = new CachingConnectionFactory();
    connectionFactory.setHost(brokerRunning.getHostName());
    connectionFactory.setPort(brokerRunning.getPort());
    connectionFactory.setUsername(brokerRunning.getUser());
    connectionFactory.setPassword(brokerRunning.getPassword());
    return connectionFactory;
}

LongRunningIntegrationTest

LongRunningIntegrationTest is a rule that disables long running tests; you might want to use this on a developer system but ensure that the rule is disabled on, for example, nightly CI builds.

Usage:

@Rule
public LongRunningIntegrationTest longTests = new LongRunningIntegrationTest();

To disable the rule at runtime, set an environment variable RUN_LONG_INTEGRATION_TESTS to true.