23. Redis Support

Since version 2.1 Spring Integration introduces support for Redis: "an open source advanced key-value store". This support comes in the form of a Redis-based MessageStore as well as Publish-Subscribe Messaging adapters that are supported by Redis via its PUBLISH, SUBSCRIBE and UNSUBSCRIBE commands.

23.1 Introduction

To download, install and run Redis please refer to the Redis documentation.

23.2 Connecting to Redis

To begin interacting with Redis you first need to connect to it. Spring Integration uses support provided by another Spring project, Spring Data Redis, which provides typical Spring constructs: ConnectionFactory and Template. Those abstractions simplify integration with several Redis-client Java APIs. Currently Spring-Data-Redis supports jedis, jredis and rjc

RedisConnectionFactory

To connect to Redis you would use one of the implementations of the RedisConnectionFactory interface:

public interface RedisConnectionFactory extends PersistenceExceptionTranslator {

	/**
	 * Provides a suitable connection for interacting with Redis.
	 *
	 * @return connection for interacting with Redis.
	 */
	RedisConnection getConnection();
}

The example below shows how to create a JedisConnectionFactory.

In Java:

JedisConnectionFactory jcf = new JedisConnectionFactory();
jcf.afterPropertiesSet();

Or in Spring's XML configuration:

<bean id="redisConnectionFactory"
    class="o.s.data.redis.connection.jedis.JedisConnectionFactory">
    <property name="port" value="7379" />
</bean>

The implementations of RedisConnectionFactory provide a set of properties such as port and host that can be set if needed. Once an instance of RedisConnectionFactory is created, you can create an instance of RedisTemplate and inject it with the RedisConnectionFactory.

RedisTemplate

As with other template classes in Spring (e.g., JdbcTemplate, JmsTemplate) RedisTemplate is a helper class that simplifies Redis data access code. For more information about RedisTemplate and its variations (e.g., StringRedisTemplate) please refer to the Spring-Data-Redis documentation

The code below shows how to create an instance of RedisTemplate:

In Java:

RedisTemplate rt = new RedisTemplate<String, Object>();
rt.setConnectionFactory(redisConnectionFactory);

Or in Spring's XML configuration::

<bean id="redisTemplate" class="org.springframework.data.redis.core.RedisTemplate">
	<property name="connectionFactory" ref="redisConnectionFactory"/>
</bean>

23.3 Messaging with Redis

As mentioned in the introduction Redis provides support for Publish-Subscribe messaging via its PUBLISH, SUBSCRIBE and UNSUBSCRIBE commands. As with JMS and AMQP, Spring Integration provides Message Channels and adapters for sending and receiving messages via Redis.

23.3.1 Redis Publish/Subscribe channel

Similar to the JMS there are cases where both the producer and consumer are intended to be part of the same application, running within the same process. This could be accomplished by using a pair of inbound and outbound Channel Adapters, however just like with Spring Integration's JMS support, there is a simpler approach to address this use case.

<int-redis:publish-subscribe-channel id="redisChannel" topic-name="si.test.topic"/>

The publish-subscribe-channel (above) will behave much like a normal <publish-subscribe-channel/> element from the main Spring Integration namespace. It can be referenced by both input-channel and output-channel attributes of any endpoint. The difference is that this channel is backed by a Redis topic name - a String value specified by the topic-name attribute. However unlike JMS this topic doesn't have to be created in advance or even auto-created by Redis. In Redis topics are simple String values that play the role of an address, and all the producer and consumer need to do to communicate is use the same String value as their topic name. A simple subscription to this channel means that asynchronous pub-sub messaging is possible between the producing and consuming endpoints, but unlike the asynchronous Message Channels created by adding a <queue/> sub-element within a simple Spring Integration <channel/> element, the Messages are not just stored in an in-memory queue. Instead those Messages are passed through Redis allowing you to rely on its support for persistence and clustering as well as its interoperability with other non-java platforms.

23.3.2 Redis Inbound Channel Adapter

The Redis-based Inbound Channel Adapter adapts incoming Redis messages into Spring Integration Messages in the same way as other inbound adapters. It receives platform-specific messages (Redis in this case) and converts them to Spring Integration Messages using a MessageConverter strategy.

<int-redis:inbound-channel-adapter id="redisAdapter"
       topics="foo, bar"
       channel="receiveChannel"
       error-channel="testErrorChannel"
       message-converter="testConverter" />

<bean id="redisConnectionFactory"
    class="o.s.data.redis.connection.jedis.JedisConnectionFactory">
    <property name="port" value="7379" />
</bean>

<bean id="testConverter" class="foo.bar.SampleMessageConverter" />

Above is a simple but complete configuration of a Redis Inbound Channel Adapter. Note that the above configuration relies on the familiar Spring paradigm of auto-discovering certain beans. In this case the redisConnectionFactory is implicitly injected into the adapter. You can of course specify it explicitly using the connection-factory attribute instead.

Also, note that the above configuration injects the adapter with a custom MessageConverter. The approach is similar to JMS where MessageConverters are used to convert between Redis Messages and the Spring Integration Message payloads. The default is a SimpleMessageConverter.

Inbound adapters can subscribe to multiple topic names hence the comma-delimited set of values in the topics attribute.

Since Spring Integration 3.0, the Inbound Adapter, in addition to the existing topics attribute, now has the topic-patterns attribute. This attribute contains a comma-delimited set of Redis topic patterns. For more information regarding Redis publish/subscribe, see Redis Pub/Sub.

Inbound adapters can use a RedisSerializer to deserialize the body of Redis Messages. The serializer attribute of the <int-redis:inbound-channel-adapter> can be set to an empty string, which results in a null value for the RedisSerializer property. In this case the raw byte[] bodies of Redis Messages are provided as the message payloads.

23.3.3 Redis Outbound Channel Adapter

The Redis-based Outbound Channel Adapter adapts outgoing Spring Integration messages into Redis messages in the same way as other outbound adapters. It receives Spring Integration messages and converts them to platform-specific messages (Redis in this case) using a MessageConverter strategy.

<int-redis:outbound-channel-adapter id="outboundAdapter"
    channel="sendChannel"
    topic="foo"
    message-converter="testConverter"/>

<bean id="redisConnectionFactory"
    class="o.s.data.redis.connection.jedis.JedisConnectionFactory">
    <property name="port" value="7379"/>
</bean>

<bean id="testConverter" class="foo.bar.SampleMessageConverter" />

As you can see the configuration is similar to the Redis Inbound Channel Adapter. The adapter is implicitly injected with a RedisConnectionFactory which was defined with 'redisConnectionFactory' as its bean name. This example also includes the optional, custom MessageConverter (the 'testConverter' bean).

Since Spring Integration 3.0, the <int-redis:outbound-channel-adapter>, as an alternative to the topic attribute, has the topic-expression attribute to determine the Redis topic against the Message at runtime. These attributes are mutually exclusive.

23.3.4 Redis Queue Inbound Channel Adapter

Since Spring Integration 3.0, a Queue Inbound Channel Adapter is available to 'right pop' messages from a Redis List. The adapter is message-driven using an internal listener thread and does not use a poller.

<int-redis:queue-inbound-channel-adapter id="" 1
                    channel="" 2
                    auto-startup="" 3
                    phase="" 4
                    connection-factory="" 5
                    queue="" 6
                    error-channel="" 7
                    serializer="" 8
                    receive-timeout="" 9
                    recovery-interval="" 10
                    expect-message="" 11
                    task-executor=""/> 12
		

1

The component bean name. If the channel attribute isn't provided a DirectChannel is created and registered with application context with this id attribute as the bean name. In this case, the endpoint itself is registered with the bean name id + '.adapter'.

2

The MessageChannel to which to send Messages from this Endpoint.

3

A SmartLifecycle attribute to specify whether this Endpoint should start automatically after the application context start or not. Default is true.

4

A SmartLifecycle attribute to specify the phase in which this Endpoint will be started. Default is 0.

5

A reference to a RedisConnectionFactory bean. Defaults to redisConnectionFactory.

6

The name of the Redis List on which the queue-based 'right pop' operation is performed to get Redis messages.

7

The MessageChannel to which to send ErrorMessages with Exceptions from the listening task of the Endpoint. By default the underlying MessagePublishingErrorHandler uses the default errorChannel from the application context.

8

The RedisSerializer bean reference. Can be an empty string, which means 'no serializer'. In this case the raw byte[] from the inbound Redis message is sent to the channel as the Message payload. By default it is a JdkSerializationRedisSerializer.

9

The timeout in milliseconds for 'right pop' operation to wait for a Redis message from the queue. Default is 1 second.

10

The time in milliseconds for which the listener task should sleep after exceptions on the 'right pop' operation, before restarting the listener task.

11

Specify if this Endpoint expects data from the Redis queue to contain entire Messages. If this attribute is set to true, the serializer can't be an empty string because messages require some form of deserialization (JDK serialization by default). Default is false.

12

A reference to a Spring TaskExecutor (or standard JDK 1.5+ Executor) bean. It is used for the underlying listening task. By default a SimpleAsyncTaskExecutor is used.

23.3.5 Redis Queue Outbound Channel Adapter

Since Spring Integration 3.0, a Queue Outbound Channel Adapter is available to 'left push' to a Redis List from Spring Integration messages:

<int-redis:queue-outbound-channel-adapter id="" 1
                    channel="" 2
                    connection-factory="" 3
                    queue="" 4
                    queue-expression="" 5
                    serializer="" 6
                    extract-payload="" />7
			  

1

The component bean name. If the channel attribute isn't provided, a DirectChannel is created and registered with the application context with this id attribute as the bean name. In this case, the endpoint is registered with the bean name id + '.adapter'.

2

The MessageChannel from which this Endpoint receives Messages.

3

A reference to a RedisConnectionFactory bean. Defaults to redisConnectionFactory.

4

The name of the Redis List on which the queue-based 'left push' operation is performed to send Redis messages. This attribute is mutually exclusive with queue-expression.

5

A SpEL Expression to determine the name of the Redis List using the incoming Message at runtime as the #root variable. This attribute is mutually exclusive with queue.

8

A RedisSerializer bean reference. By default it is a JdkSerializationRedisSerializer. However, for String payloads, a StringRedisSerializer is used, if a serializer reference isn't provided.

7

Specify if this Endpoint should send just the payload to the Redis queue, or the entire Message. Default is true .

23.3.6 Redis Application Events

Since Spring Integration 3.0, the Redis module provides an implementation of IntegrationEvent - which, in turn, is a org.springframework.context.ApplicationEvent. The RedisExceptionEvent encapsulates an Exceptions from Redis operations (with the Endpoint being the source of the event). For example, the <int-redis:queue-inbound-channel-adapter/> emits those events after catching Exceptions from the BoundListOperations.rightPop operation. The exception may be any generic org.springframework.data.redis.RedisSystemException or a org.springframework.data.redis.RedisConnectionFailureException. Handling these events using an <int-event:inbound-channel-adapter/> can be useful to determine problems with background Redis tasks and to take administrative actions.

23.4 Redis Message Store

As described in EIP, a Message Store allows you to persist Messages. This can be very useful when dealing with components that have a capability to buffer messages (Aggregator, Resequencer, etc.) if reliability is a concern. In Spring Integration, the MessageStore strategy also provides the foundation for the ClaimCheck pattern, which is described in EIP as well.

Spring Integration's Redis module provides the RedisMessageStore.

<bean id="redisMessageStore" class="o.s.i.redis.store.RedisMessageStore">
    <constructor-arg ref="redisConnectionFactory"/>
</bean>

<int:aggregator input-channel="inputChannel" output-channel="outputChannel"
         message-store="redisMessageStore"/>

Above is a sample RedisMessageStore configuration that shows its usage by an Aggregator. As you can see it is a simple bean configuration, and it expects a RedisConnectionFactory as a constructor argument.

By default the RedisMessageStore will use Java serialization to serialize the Message. However if you want to use a different serialization technique (e.g., JSON), you can provide your own serializer via the valueSerializer property of the RedisMessageStore.

23.4.1 Redis Channel Message Stores

The RedisMessageStore above maintains each group as a value under a single key (the group id). While this can be used to back a QueueChannel for persistence, a specialized RedisChannelMessageStore is provided for that purpose (since version 4.0). This store uses a LIST for each channel and LPUSH when sending and RPOP when receiving messages. This store also uses JDK serialization by default, but the value serializer can be modified as described above.

It is recommended that this store is used for backing channels, instead of the general RedisMessageStore.

<bean id="redisMessageStore" class="o.s.i.redis.store.RedisChannelMessageStore">
	<constructor-arg ref="redisConnectionFactory"/>
</bean>

<int:channel id="somePersistentQueueChannel">
	<int:queue message-store="redisMessageStore"/>
<int:channel>

The keys that are used to store the data have the form <storeBeanName>:<channelId> (in the above example, redisMessageStore:somePersistentQueueChannel).

In addition, a subclass RedisChannelPriorityMessageStore is also provided. When this is used with a QueueChannel, the messages are received in (FIFO within) priority order. It uses the standard IntegrationMessageHeaderAccessor.PRIORITY header and supports priority values 0 - 9; messages with other priorities (and messages with no priority) are retrieved in FIFO order after any messages with priority.

[Important]Important
These stores implement only BasicMessageGroupStore and do not implement MessageGroupStore; they can only be used for situations such as backing a QueueChannel.

23.5 Redis Metadata Store

As of Spring Integration 3.0 a new Redis-based MetadataStore (Section 8.4, “Metadata Store”) implementation is available. The RedisMetadataStore can be used to maintain state of a MetadataStore across application restarts. This new MetadataStore implementation can be used with adapters such as:

In order to instruct these adapters to use the new RedisMetadataStore simply declare a Spring bean using the bean name metadataStore. The Twitter Inbound Channel Adapter and the Feed Inbound Channel Adapter will both automatically pick up and use the declared RedisMetadataStore.

<bean name="metadataStore" class="o.s.i.redis.store.metadata.RedisMetadataStore">
    <constructor-arg name="connectionFactory" ref="redisConnectionFactory"/>
</bean>

The RedisMetadataStore is backed by RedisProperties and interaction with it uses BoundHashOperations, which, in turn, requires a key for the entire Properties store. In the case of the MetadataStore, this key plays the role of a region, which is useful in distributed environment, when several applications use the same Redis server. By default this key has the value MetaData.

Starting with version 4.0, this store now implements ConcurrentMetadataStore, allowing it to be reliably shared across multiple application instances where only one instance will be allowed to store or modify a key's value.

23.6 RedisStore Inbound Channel Adapter

The RedisStore Inbound Channel Adapter is a polling consumer that reads data from a Redis collection and sends it as a Message payload.

<int-redis:store-inbound-channel-adapter id="listAdapter"
    connection-factory="redisConnectionFactory"
    key="myCollection"
    channel="redisChannel"
    collection-type="LIST" >
    <int:poller fixed-rate="2000" max-messages-per-poll="10"/>
</int-redis:store-inbound-channel-adapter>

As you can see from the configuration above you configure a Redis Store Inbound Channel Adapter using the store-inbound-channel-adapter element, providing values for various attributes such as:

  • key or key-expression - The name of the key for the collection being used.
  • collection-type - enumeration of the Collection types supported by this adapter. Supported Collections are: LIST, SET, ZSET, PROPERTIES, MAP
  • connection-factory - reference to an instance of o.s.data.redis.connection.RedisConnectionFactory
  • redis-template - reference to an instance of o.s.data.redis.core.RedisTemplate

and other attributes that are common across all other inbound adapters (e.g., 'channel').

[Note]Note
You cannot set both redis-template and connection-factory.
[Important]Important
By default, the adapter uses a StringRedisTemplate; this uses StringRedisSerializers for keys, values, hash keys and hash values. If your Redis store contains objects that are serialized with other techniques, you must supply a RedisTemplate configured with appropriate serializers. For example, if the store is written to using a RedisStore Outbound Adapter that has its extract-payload-elements set to false, you must provide a RedisTemplate configured thus:
<bean id="redisTemplate" class="org.springframework.data.redis.core.RedisTemplate">
    <property name="connectionFactory" ref="redisConnectionFactory"/>
    <property name="keySerializer">
        <bean class="org.springframework.data.redis.serializer.StringRedisSerializer"/>
    </property>
    <property name="hashKeySerializer">
        <bean class="org.springframework.data.redis.serializer.StringRedisSerializer"/>
    </property>
</bean>

This uses String serializers for keys and hash keys and the default JDK Serialization serializers for values and hash values.

The example above is relatively simple and static since it has a literal value for the key. Sometimes, you may need to change the value of the key at runtime based on some condition. To do that, simply use key-expression instead, where the provided expression can be any valid SpEL expression.

Also, you may wish to perform some post-processing to the successfully processed data that was read from the Redis collection. For example; you may want to move or remove the value after its been processed. You can do this using the Transaction Synchronization feature that was added with Spring Integration 2.2.

<int-redis:store-inbound-channel-adapter id="zsetAdapterWithSingleScoreAndSynchronization"
        connection-factory="redisConnectionFactory"
        key-expression="'presidents'"
        channel="otherRedisChannel"
        auto-startup="false"
        collection-type="ZSET">
            <int:poller fixed-rate="1000" max-messages-per-poll="2">
                <int:transactional synchronization-factory="syncFactory"/>
            </int:poller>
</int-redis:store-inbound-channel-adapter>

<int:transaction-synchronization-factory id="syncFactory">
	<int:after-commit expression="payload.removeByScore(18, 18)"/>
</int:transaction-synchronization-factory>

<bean id="transactionManager" class="o.s.i.transaction.PseudoTransactionManager"/>

As you can see from the above all, you need to do is declare your poller to be transactional with a transactional element. This element can reference a real transaction manager (for example if some other part of your flow invokes JDBC). If you don't have a 'real' transaction, you can use a o.s.i.transaction.PseudoTransactionManager which is an implementation of Spring's PlatformTransactionManager and enables the use of the transaction synchronization features of the redis adapter when there is no actual transaction.

[Important]Important
This does NOT make the Redis activities themselves transactional, it simply allows the synchronization of actions to be taken before/after success (commit) or after failure (rollback).

Once your poller is transactional all you need to do is set an instance of the org.springframework.integration.transaction.TransactionSynchronizationFactory on the transactional element. TransactionSynchronizationFactory will create an instance of the TransactionSynchronization. For your convenience we've exposed a default SpEL-based TransactionSynchronizationFactory which allows you to configure SpEL expressions, with their execution being coordinated (synchronized) with a transaction. Expressions for before-commit, after-commit, and after-rollback are supported, together with a channel for each where the evaluation result (if any) will be sent. For each sub-element you can specify expression and/or channel attributes. If only the channel attribute is present the received Message will be sent there as part of the particular synchronization scenario. If only the expression attribute is present and the result of an expression is a non-Null value, a Message with the result as the payload will be generated and sent to a default channel (NullChannel) and will appear in the logs (DEBUG). If you want the evaluation result to go to a specific channel add a channel attribute. If the result of an expression is null or void, no Message will be generated.

For more information about transaction synchronization, see Section C.3, “Transaction Synchronization”.

23.7 RedisStore Outbound Channel Adapter

The RedisStore Outbound Channel Adapter allows you to write a Message payload to a Redis collection

<int-redis:store-outbound-channel-adapter id="redisListAdapter"
          collection-type="LIST"
          channel="requestChannel"
          key="myCollection" />

As you can see from the configuration above, you configure a Redis Store Outbound Channel Adapter using the store-inbound-channel-adapter element, providing values for various attributes such as:

  • key or key-expression - The name of the key for the collection being used.
  • extract-payload-elements - If set to true (Default) and the payload is an instance of a "multi- value" object (i.e., Collection or Map) it will be stored using addAll/ putAll semantics. Otherwise, if set to false the payload will be stored as a single entry regardless of its type. If the payload is not an instance of a "multi-value" object, the value of this attribute is ignored and the payload will always be stored as a single entry.
  • collection-type - enumeration of the Collection types supported by this adapter. Supported Collections are: LIST, SET, ZSET, PROPERTIES, MAP
  • map-key-expression - SpEL expression that returns the name of the key for entry being stored. Only applies if the collection-type is MAP or PROPERTIES and 'extract-payload-elements' is false.
  • connection-factory - reference to an instance of o.s.data.redis.connection.RedisConnectionFactory
  • redis-template - reference to an instance of o.s.data.redis.core.RedisTemplate

and other attributes that are common across all other inbound adapters (e.g., 'channel').

[Note]Note
You cannot set both redis-template and connection-factory.
[Important]Important
By default, the adapter uses a StringRedisTemplate; this uses StringRedisSerializers for keys, values, hash keys and hash values. However, if extract-payload-elements is set to false, a RedisTemplate using StringRedisSerializers for keys and hash keys, and JdkSerializationRedisSerializers for values and hash values will be used. With the JDK serializer, it is important to understand that java serialization is used for all values, regardless of whether the value is actually a collection or not. If you need more control over the serialization of values, you may want to consider providing your own RedisTemplate rather than relying upon these defaults.

The example above is relatively simple and static since it has a literal values for the key and other attributes. Sometimes you may need to change the values dynamically at runtime based on some condition. To do that simply use their -expression equivalents (key-expression, map-key-expression etc.) where the provided expression can be any valid SpEL expression.

23.8 Redis Outbound Command Gateway

Since Spring Integration 4.0, the Redis Command Gateway is available to perform any standard Redis command using generic RedisConnection#execute method:

<int-redis:outbound-gateway
		request-channel="" 1
		reply-channel="" 2
		requires-reply="" 3
		reply-timeout="" 4
		connection-factory="" 5
		redis-template="" 6
		arguments-serializer="" 7
		command-expression="" 8
		argument-expressions="" 9
		use-command-variable="" 10
		arguments-strategy="" />11
			

1

The MessageChannel from which this Endpoint receivesMessages.

2

The MessageChannel where this Endpoint sends replyMessages.

3

Specify whether this outbound gateway must return a non-null value. This value is false by default, otherwise a ReplyRequiredException will be thrown when the Redis returns a null value.

4

The timeout in milliseconds to wait until the reply message will be sent or not. Typically is applied for queue-based limited reply-channels.

5

A reference to a RedisConnectionFactorybean. Defaults to redisConnectionFactory. Mutually exclusive with 'redis-template' attribute.

6

A reference to a RedisTemplate bean. Mutually exclusive with 'connection-factory' attribute.

7

Reference to an instance oforg.springframework.data.redis.serializer.RedisSerializer. Used to serialize each command argument to byte[] if necessary.

8

The SpEL expression that returns the command key. Default is the redis_command message header. Must not evaluate to null.

9

Comma-separate SpEL expressions that will be evaluated as command arguments. Mutually exclusive with the arguments-strategy attribute. If neither of them is provided the payload is used as the command argument(s). Argument expressions may evaluate to 'null', to support a variable number of arguments.

10

A boolean flag to specify if the evaluated Redis command string will be made available as the #cmd variable in the expression evaluation context in the org.springframework.integration.redis.outbound.ExpressionArgumentsStrategy when argument-expressions is configured, otherwise this attribute is ignored.

11

Reference to an instance of org.springframework.integration.redis.outbound.ArgumentsStrategy. Mutually exclusive with argument-expressions attribute. If neither of them is provided the payload is used as the command argument(s).

The <int-redis:outbound-gateway> can be used as a common component to perform any desired Redis operation. For example to get incremented value from Redis Atomic Number:

<int-redis:outbound-gateway request-channel="requestChannel"
	reply-channel="replyChannel"
	command-expression="'INCR'"/>

where the Message payload should be a name of redisCounter, which may be provided by org.springframework.data.redis.support.atomic.RedisAtomicInteger bean definition.

The RedisConnection#execute has a generic Object as return type and real result depends on command type, for example MGET returns a List<byte[]>. For more information about commands, their arguments and result type see Redis Specification.

23.9 Redis Lock Registry

Starting with version 4.0, the RedisLockRegistry is available. Certain components (for example aggregator and resequencer) use a lock obtained from a LockRegistry instance to ensure that only one thread is manipulating a group at a time. The DefaultLockRegistry performs this function within a single component; you can now configure an external lock registry on these components. When used with a shared MessageGroupStore, the RedisLockRegistry can be use to provide this functionality across multiple application instances, such that only one instance can manipulate the group at a time.

When a lock is released by a local thread, another local thread will generally be able to acquire the lock immediately. If a lock is released by a thread using a different registry instance, it can take up to 100ms to acquire the lock.

To avoid "hung" locks (when a server fails), the locks in this registry are expired after a default 60 seconds, but this can be configured on the registry. Locks are normally held for a much smaller time.

[Important]Important
Because the keys can expire, an attempt to unlock an expired lock will result in an exception being thrown. However, be aware that the resources protected by such a lock may have been compromised so such exceptions should be considered severe. The expiry should be set at a large enough value to prevent this condition, while small enough that the lock can be recovered after a server failure in a reasonable amount of time.