Concepts

The LittleHorse Quarkus extension uses annotations to declare tasks, workflows, structs, and user task forms. At startup, it discovers these types, registers them with the LittleHorse Kernel, and starts task workers.

Annotations

Tasks and Workflows

• @LHTask: Marks a class as a LittleHorse task definition. Methods annotated with @LHTaskMethod become Task Workers.
• @LHWorkflow: Marks a method as a workflow definition. The method receives a WorkflowThread and defines the WfSpec.
• @LHTaskMethod: Marks a method as the handler for a specific TaskDef.

Structs

• @LHStructDef: Marks a class as a StructDef. Use it for typed, structured data in workflows and tasks.

User Tasks

• @LHUserTaskForm: Marks a class as a User Task form definition. Use @UserTaskField on fields to define the form schema.

Registration

The extension scans your application for beans annotated with @LHTask, @LHWorkflow, @LHStructDef, and @LHUserTaskForm. It registers them with the LittleHorse Kernel at startup before the application is ready to serve requests.

You can disable registration globally or per-task, per-workflow, per-user-task, or per-struct via configuration. See Configuration.

Injected Clients

The extension provides two gRPC clients you can inject:

• LittleHorseBlockingStub — For synchronous calls. Use it in REST endpoints, services, or any blocking code.
• LittleHorseReactiveStub — For reactive calls. Use it with Uni and Multi in Quarkus reactive code.

Both clients use the same LittleHorse client configuration (environment variables, properties file, or LHConfig).

Hierarchical Workflows

You can define child workflows that run under a parent. Use the parent attribute of @LHWorkflow:

@LHWorkflow(PARENT_WF)
public void parent(WorkflowThread wf) {
    wf.execute(GREETINGS_TASK, PARENT_WF, wf.declareStr(NAME_VARIABLE).asPublic());
}

@LHWorkflow(value = CHILD_WF, parent = PARENT_WF)
public void child(WorkflowThread wf) {
    wf.execute(GREETINGS_TASK, CHILD_WF, wf.declareStr(NAME_VARIABLE).asInherited());
}

Retry Policies

Use @LHExponentialBackoffRetry as an attribute of @LHWorkflow to configure default retry behavior for task nodes. You can use config property placeholders:

@LHWorkflow(
    value = "my-workflow",
    defaultTaskExponentialBackoffRetry = @LHExponentialBackoffRetry(
        baseIntervalMs = "${retry.base.interval.ms}",
        maxDelayMs = "${retry.max.delay.ms}",
        multiplier = "${retry.multiplier}"))
public void workflow(WorkflowThread wf) {
    wf.execute("my-task", wf.declareStr("input").required());
}

Configure the values in application.properties:

retry.base.interval.ms=1000
retry.max.delay.ms=10000
retry.multiplier=2.0

StructDef Compatibility

When registering structs, you can control schema compatibility. See the structs configuration section.