This example demonstrates the use of a process barrier component to suspend a thread until some asynchronous operation completes. The first example uses an HTTP Inbound Gateway, splits the request, sends the splits to rabbitmq and then waits for the publisher confirms. Finally, the results are returned to the caller.

The sample is a Spring Boot application that loads 2 contexts:

• Client - Sends A,B,C to the server
• Server - Web application

The server context has 3 integration flows:

http -> splitter -> amqp
     |-> barrier

amqp(Acks) -> aggregator -> barrier (release)

qmqp(inbound) -> nullChannel

The last flow drains the messages and allows the auto-delete queue to be removed when the application is closed.

$ gradlew :barrier:run

This will package the application and run it using the Gradle Application Plugin

In STS (Eclipse), go to package org.springframework.integration.samples.barrier, right-click Application and select Run as --> Java Application (or Spring Boot Application).

The gateway (client) initiates a simple request posting "A,B,C" to the server and the server responds with the results. You should see the following output from the server:

++++++++++++ Replied with: Result: A: ack=true, B: ack=true, C: ack=true ++++++++++++

The second example uses a simple gateway to launch some asynchronous tasks and waits for those tasks to complete.

It shows how you might return an exception to the caller if one or more of those tasks fail.

An aggregator is used to aggregate the results; if there are no errors, the results are returned; if one or more errors occurred, an exception is sent to release the barrier; this is thrown to the caller and has all the consolidated results in a property.

You can run this example from an IDE, such as STS using the technique above; in this case, the class is ErrorHandlingApplication in the org.springframework.integration.samples.barrier package.

It sends a list of integers to the flow:

[2, 0, 2, 0, 2]

The zeros should fail and in stderr you should see the results:

ConsolidatedResultsException
[results=
[5
org.springframework.integration.transformer.MessageTransformationException:
  Failed to transform Message; nested exception is org.springframework.messaging.MessageHandlingException:
  Expression evaluation failed: 10 / payload; nested exception is java.lang.ArithmeticException: / by zero
5
org.springframework.integration.transformer.MessageTransformationException:
  Failed to transform Message; nested exception is org.springframework.messaging.MessageHandlingException:
  Expression evaluation failed: 10 / payload; nested exception is java.lang.ArithmeticException: / by zero
5]
]