We are pleased to announce that the Spring Integration 4.0 release candidate (4.0.0.RC1) is now available. Please use the Milestone Repository with maven or gradle, download a distribution archive, or see the project home page for links to the updated documentation, and Maven/Gradle configuration details.

The release includes several bug fixes, some new features and further improvements with the GA release due near the end of April.

Here is a summary of major changes since the last milestone

@Poller and @InboundChannelAdapter

Building on the extensive improvements to annotation support announced in M4 Release, the new @Poller annotation has been added to each of the Messaging Annotations (@ServiceActivator, @Router etc.). The @Poller annotation attribute enables configuration of poller options for the inputChannel of the Messaging Annotation. This allows annotated endpoints to be PollingConsumers. Previously, annotated endpoints could only use SubscribableChannels and be event-driven.

This also provided the ability for us to introduce the @InboundChannelAdapter method Messaging Annotation. Now it can be configured without using XML, in a Spring Boot application, for example:

@EnableAutoConfiguration  // enables integration infrastructure
@MessageEndpoint          // makes this class as an integration component
@PropertySource("classpath:integration.properties") // property-placeholder configuration
public class Integration {

    public static void main(String[] args) throws Exception {
        ConfigurableApplicationContext ctx = SpringApplication.run(Integration.class, args);
        Thread.sleep(10000);
        ctx.close();
    }

	@InboundChannelAdapter(value = "countChannel",
         poller = @Poller(fixedDelay = "${poller.interval}", maxMessagesPerPoll = "1"))
	public Integer count() {
		return this.counter.incrementAndGet();
	}

 	@ServiceActivator(inputChannel="countChannel")
    public void foo(Integer payload) {
        System.out.println(payload);
    }
        
}

This is equavalent to the following XML configuration:

<int:inbound-channel-adapter channel="countChannel" ref="counter" method="incrementAndGet">
	<int:poller fixed-delay="${poller.interval}" max-messages-per-poll="1"/>
</int:inbound-channel-adapter>

<int-stream:stdout-channel-adapter id="countChannel"/>

Distributed MetadataStore and LockRegistry

The MetadataStore is designed to store various types of generic meta-data (e.g., published date of the last feed entry that has been processed) to help components, such as the Feed Adapter, to maintain state, and avoid duplicates. For a distributed environment, and multi-instance applications, and to have persistent metadata state to be maintained across application restarts, the RedisMetadataStore and GemfireMetadataStore have been introduced with this release.

For example, a <int-file:inbound-channel-adapter> can be configured with a FileSystemPersistentAcceptOnceFileListFilter, which can be configured to use one of these distributed MetadataStores. This allows filter keys to be shared across multiple application instances, or when a network file share is being used by multiple servers.

For similar distributed (cross-JVM) environments, when only one instance can have access to the object (e.g. AggregatorHandler for MessageGroup on message arrival), distributed LockRegistry implementations have been introduced - RedisLockRegistry and GemfireLockRegistry.

Aggregator automatic group release

The <aggregator> and <resequencer> endpoints can now have a group-timeout or group-timeout-expression option to allow these Correlating Endpoints to take action after a group has been idle for some time. Previously, you had to configure an external MessagGroupStoreReaper for this purpose. The groupTimeout property schedules the MessageGroup to be forced complete some time after a Message arrives where that event does not cause the ReleaseStrategy to release the group.

Perhaps more interesting from this perspective, is the group-timeout-expression. It allows dynamic determination of the groupTimeout value at runtime based on the state of the group at the time the message arrives. For example:

<aggregator input-channel="input" output-channel="output" discard-channel="discard"
        send-partial-result-on-expiry="true"
        group-timeout-expression="size() ge 2 ? 1000 : -1"
        release-strategy="someReleaseStrategy"/>

In this case, the group will never timeout if there is only 1 messdage in the group, but the Aggregator will send the partial MessageGroup automatically after being idle for 1 second, as long as the group contains at least 2 messages.

Priority Channel and Message Store

With this release, you can configure a <priority-queue> using an external MessageStore. For this purpose we have introduced the new PriorityCapableChannelMessageStore strategy and provided implementations for JDBC, Redis and MongoDB. This now allows message persistence in priority channels.

Twitter Search Gateway

The existing twitter <search-inbound-channel-adapter> only allows a fixed query to be executed on each poll. For more flexibility, the <int-twitter:search-outbound-gateway/> has been added as a component to perform arbitrary request/reply Twitter Search operations, based on a search-args-expression. The default is payload, which can be a search String or an instance of org.springframework.social.twitter.api.SearchParameters. However this attribute can be configred in SpEL as:

"new SearchParameters(payload).count(5).sinceId(headers.sinceId)"

or:

"{payload, 30}"

as a SpEL inline list - in this case the query string and page size, or...

"{payload, headers.pageSize, headers.sinceId, headers.maxId}"

The four arguments of org.springframework.social.twitter.api.SearchOperations#search. For more information see Spring Social Twitter documentation.

Wrapping up

For a complete list of changes refer to the release notes, What's New and Java Docs of the new components.

We look forward to your comments and feedback (Spring Forum, StackOverflow (spring-integration tag), Spring JIRA) as soon as possible and report issues you find before we GA towards the end of the month.

SpringOne 2GX 2014 is around the corner

Book your place at SpringOne in Dallas, TX for Sept 8-11 soon. It's simply the best opportunity to find out first hand all that's going on and to provide direct feedback. Expect a number of significant new announcements this year. We are anticipating that several in-depth Spring-Integration sessions will be presented.