This example contains a simple workflow service that illustrates callback state using OpenAPI callbacks functionality. A callback is a state that invokes an action and wait for an event (event that will be eventually fired by the external service notified by the action). This example consists of a callback state that waits for an event to arrive at the wait channel. Its action calls an external service that publishes the wait event over HTTP. After consuming the wait event, the workflow prints the message received in the wait event and ends the workflow.

To go further on using HTTP with Reactive Messaging, take a look at this article.

For information related to Open API callbacks functionality, please refer this document.

The service is described using JSON format as defined in the CNCF Serverless Workflow specification.

Installing and Running

Prerequisites

You will need:

Java 17+ installed
Environment variable JAVA_HOME set accordingly
Maven 3.9.6+ installed When using native image compilation, you will also need:
GraalVm 19.3.1+ installed
Environment variable GRAALVM_HOME set accordingly
Note that GraalVM native image compilation typically requires other packages (glibc-devel, zlib-devel and gcc) to be installed too. You also need 'native-image' installed in GraalVM (using 'gu install native-image'). Please refer to GraalVM installation documentation for more details.

Run the following commands from the callback-workflow directory as per the selected mode of running.

Compile and Run in Local Dev Mode

mvn clean package quarkus:dev

Compile and Run in JVM mode

mvn clean package 
java -jar target/quarkus-app/quarkus-run.jar

or on Windows

mvn clean package
java -jar target\quarkus-app\quarkus-run.jar

Compile and Run using Local Native Image

Note that this requires GRAALVM_HOME to point to a valid GraalVM installation

mvn clean package -Pnative

To run the generated native executable, generated in target/, execute

./target/serverless-workflow-compensation-quarkus-{version}-runner

In another terminal, run the callback event service using the below command

mvn clean package quarkus:dev -Dquarkus.http.port=8181

Submit a request

The service based on the JSON workflow definition can be accessed by sending a request to http://localhost:8080/callback with the following content

{
  "message": "Hello"
}

Complete curl command can be found below:

curl -X POST -H 'Content-Type:application/json' -H 'Accept:application/json' -d '{"message": "Hello"}' http://localhost:8080/callback

Should return something like this ("id" will change):

{
  "id":"f9a75f77-7269-4b18-93cd-2955e3406cd4",
  "workflowdata":{
    "message":"New Event"
  }
}