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Spring Integration Java DSL 1.0 RC1 Released

Dear Spring community,

We are pleased to announce that soon after the
Spring Integration 4.1 Release Candidate
the Spring Integration Java DSL 1.0 Release Candidate is now available.
Please use the Milestone Repository with Maven or Gradle,
or download a
distribution archive,
to give it a spin.

See the project home page
for more information.

The release includes many new features and improvements, as well as a number of bug fixes. The GA release
is planned for the middle of November.

Here is a summary of major changes since the
last milestone:

Refactoring and Breaking Changes

While still supporting earlier Java versions, the Spring Integration Java DSL is primarily positioned for Java 8 and its Lambda support.
We have removed several
functional interfaces in favor of similar interfaces from Java 8: Consumer<T>, Function<T, R> etc. Of course, to support
backward compatibility with older Java version we have implemented similar interfaces in the DSL source code. Users that
are using the changed interfaces with with Java versions less than 8 will need to make changes to fix their compilation errors. For example:

From this:

.handle(Integer.class, (p, h) -> p * 2,
		new EndpointConfigurer<GenericEndpointSpec<ServiceActivatingHandler>>() {
				@Override
				public void accept(GenericEndpointSpec<ServiceActivatingHandler> spec) {
					spec.poller(Pollers.cron("7 * * * * ?"));
				}
		})

To this:
java .handle(Integer.class, (p, h) -> p * 2, new Consumer<GenericEndpointSpec<ServiceActivatingHandler>>() { @Override public void accept(GenericEndpointSpec<ServiceActivatingHandler> spec) { spec.poller(Pollers.cron("7 * * * * ?")); } })
Of course if you use a Java 8 Lambda here, the code will not require changes:

.handle(Integer.class, (p, h) -> p * 2, e -> e.poller(Pollers.cron("7 * * * * ?")))

The IntegrationFlows now contains only from(...) methods. the .fromFixedMessageChannel() has been replaced with
.from(String messageChannelName, boolean fixedSubscriber).

In addition, to fix some package tangle issues, we have moved some classes to different packages.

Method Scope Functions

To simplify the code completion from an IDE and allow avoiding redundant searches for a desired Namespace Factory we
added overloaded methods with Function<T, R> argument. For example these code snippets are equal:
java ..... .channel(Amqp.pollableChannel(this.rabbitConnectionFactory) .queueName("amqpReplyChannel") .channelTransacted(true)) .... .channel(c -> c.amqpPollable(this.rabbitConnectionFactory) .queueName("amqpReplyChannel") .channelTransacted(true)) ....
Where the c variable is the Channel’s “method-aggregator” object, which delegates to the appropriate Namespace Factory.
Other similar Lambda methods are:

  • IntegrationFlows.from(MessageSourcesFunction sources)
  • IntegrationFlows.from(MessageProducersFunction producers)
  • IntegrationFlows.from(MessagingGatewaysFunction gateways)
  • IntegrationFlowDefinition.handleWithAdapter(Function<Adapters, MessageHandlerSpec<?, H>> adapters)
  • EndpointSpec.poller(Function<PollerFactory, PollerSpec> pollers)

FunctionExpression

Spring Integration has amazing Spring Expression Language (SpEL) support. Since the Java DSL is
pure (eh!) Java, it does not really make sense to specify some business logic in a long String for an expression property.
Being inspired by Java 8 Lambda support, and pursuing the aim of minimal changes
we have introduced the FunctionExpression - an implementation of the SpEL Expression interface - which accepts a
Function<T, R> and delegates to it on the each getValue(). Now, many components in the DSL provide
(Function<T, R> function) methods as an alternative to the similar SpEL method. Here is an example for the localFilename
property for the FtpInboundFileSynchronizingMessageSource:

With SpEL:
java @Bean public IntegrationFlow ftpInboundFlow() { return IntegrationFlows .from(s -> s.ftp(this.ftpSessionFactory) .remoteDirectory("ftpSource") .localFilenameExpression("payload.toUpperCase() + '.a'") .channel(c -> c.queue("ftpInboundResultChannel")) .get(); }

With Lambda:
java @Bean public IntegrationFlow ftpInboundFlow() { return IntegrationFlows .from(s -> s.ftp(this.ftpSessionFactory) .remoteDirectory("ftpSource") .localFilename(f -> f.toUpperCase() + ".a"))) .channel(c -> c.queue("ftpInboundResultChannel")) .get(); }
Other interesting uses of the FunctionExpression are the Enricher and HeaderEnricher:
java .enrich(e -> e.requestChannel("enrichChannel") .requestPayload(Message::getPayload) .propertyFunction("date", m -> new Date()))

The FunctionExpression also supports runtime type conversion as is done in the standard SpelExpression.

SubFlows

We have introduced SubFlow support for some if...else and publish-subscribe components. The simplest
example is .publishSubscribeChannel():
java @Bean public IntegrationFlow subscribersFlow() { return flow -> flow .publishSubscribeChannel(Executors.newCachedThreadPool(), s -> s .subscribe(f -> f .<Integer>handle((p, h) -> p / 2) .channel(c -> c.queue("subscriber1Results"))) .subscribe(f -> f .<Integer>handle((p, h) -> p * 2) .channel(c -> c.queue("subscriber2Results")))) .<Integer>handle((p, h) -> p * 3) .channel(c -> c.queue("subscriber3Results")); }
Of course the same result we can be achieved with separate IntegrationFlow @Bean definitions, but we hope you’ll
find the subflow style of logic composition useful.

Similar publish-subscribe subflow composition is provided by .routeToRecipients().

Another example is .discardFlow() instead of .discardChannel() on .filter().

.route() deserves special attention:
java @Bean public IntegrationFlow routeFlow() { return f -> f .<Integer, Boolean>route(p -> p % 2 == 0, m -> m.channelMapping("true", "evenChannel") .subFlowMapping("false", sf -> sf.<Integer>handle((p, h) -> p * 3))) .transform(Object::toString) .channel(c -> c.queue("oddChannel")); }
The .channelMapping() continues to work as in regular Router mapping, but the .subFlowMapping() tied that
subflow with main flow. In other words, any router’s subflow returns to the main flow after .route().

Similar “return-to-main-flow” subflow is supported by .gateway():
java @Bean public IntegrationFlow gatewayFlow() { return f -> f.gateway("gatewayRequest", g -> g.errorChannel("gatewayError").replyTimeout(10L)) .gateway(gf -> gf.transform("From Gateway SubFlow: "::concat)); }
However this Gateway SubFlow is just wired with main flow through the explicit DirectChannel and wrapped to
the regular GatewayMessageHandler using that channel as a requestChannel option.

Of course, subflows can be nested with any depth, but we don’t recommend to do that because, in fact, even in the
router case, adding complex subflows within a flow would quickly begin to be
difficult for a human to parse.

Conclusion

We haven’t added more protocol specific adapters since the last milestone. Not all adapters will be supported directly by the DSL
although the most commonly used ones have first class support.
However, those that don’t have first class support can easily be wired in using .handle(). As we have discussed previously,
we are looking for input to prioritize the implementations of the remaining adapters
so, don’t be shy to share your thoughts and ideas!

You can obtain more information about these and existing classes from their
source code
and from Reference Manual.

We look forward to your comments and feedback (StackOverflow (spring-integration tag),
Spring JIRA, GitHub)
as soon as possible and report issues you find before we GA towards over a couple weeks.

As always, we very much welcome contributions.

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