This example contains a simple workflow service that illustrate error handling. The service is described using JSON format as defined in the CNCF Serverless Workflow specification.

The workflow consists of a Java service that determines if a provided number is odd or even, followed by a call to a REST service to publish any even number. The main feature of this demo is to show different ways of exception handling within a workflow. In the Java service, if the number is odd, an exception is thrown, and it is the exception error handling the one that sets the odd message. If the REST service call returns a 400 response, the exception error handling mechanism causes the workflow to follow an error path instead of propagating this exception to the caller.

Hence, this workflow expects JSON input containing a natural number. This number is passed using a service operation to EvenService java class. If the number is even, the workflow moves to the next defined state, injecting "even" numberType. But if the number is odd, the class throws an IllegalArgumentException. This exception is handled and redirected to odd inject node by using inline workflow error handling. This basically consists on adding onErrors field, where the expected exception is specified in code and the target state (a node injecting "odd" numberType) in transition. Both execution paths then finish on the same node, which prints the calculated numberType.

In the next step, the workflow calls the PublishRestService via REST. This service evaluates the numberType from the previous step and either returns with a successful response if the number is even, or with a failure response (HTTP status code 400) if the number is odd. The failure event is handled as the action node contains an onError definition. The referenced error is defined as "code": "HTTP:400". If this exception is encountered, the workflow execution continues on an error path that prints out the failure.

As per 0.8 version of the specification, there is no standard way to set a process in error. To do that, users can use a custom metadata key called errorMessage which will contain either the error message to be associated to the process instance or an expression that returns the error message to associated to the process instance. In addition to the workflow described before, this example includes a file called errorWithMEtadata.sw.json that illustrate the usage of such metadata.

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.

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-error-quarkus-{version}-runner

Submit a request

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

{
  "number": 2
}

Complete curl command can be found below:

curl -X POST -H 'Content-Type:application/json' -H 'Accept:application/json' -d '{"number": 2}' http://localhost:8080/error

In Quarkus you should see the log message printed:

even

If you would like to check odd number

{
  "number": 1
}

Complete curl command can be found below:

curl -X POST -H 'Content-Type:application/json' -H 'Accept:application/json' -d '{"number": 1}' http://localhost:8080/error

In Quarkus you should see the log message printed:

odd
Fail to publish result