Level 2: Sequential Flows 🔗

Most workflows don't end in one step. In this level, we'll connect two tasks to make data flow automatically between them.

🎯 Goal

Make the workflow fetch an Order and then validate it (ValidationResult).

Step 1: Add the Validation Task

We'll add a new method to our OrderTasks. Notice that the result of fetchOrder is the input for validateOrder.

@TaskHandler("order-tasks")
public class OrderTasks {

    @FlowTask(id = "fetchOrder")
    public Mono<Order> fetchOrder(String orderId) { ... }

    @FlowTask(id = "validateOrder")
    public Mono<ValidationResult> validateOrder(Order order) {
        // FlowForge passes the Order object from the previous task here
        if (order.getAmount() > 0) {
            return Mono.just(new ValidationResult(true));
        }
        return Mono.just(new ValidationResult(false));
    }
}

Step 2: Chain with .then()

We use the .then() operator in our plan to connect the blocks using the Annotation Way.

@Component
@FlowWorkflow(id = "order-process")
public class OrderProcessWorkflow implements WorkflowDefinition {

    @Override
    public WorkflowExecutionPlan define(FlowDsl dsl) {
        return dsl.flow(OrderTasks::fetchOrder) // Returns Order
                  .then(OrderTasks::validateOrder) // Receives Order, Returns ValidationResult
                  .build();
    }
}

Step 3: Update the Service

Since the last task in our workflow is now validateOrder, the FlowForgeClient will return a ValidationResult. Also, as our business logic is growing beyond a simple "fetch", we will rename the service method to processOrder to better reflect the new reality.

@Service
public class OrderService {
    private final FlowForgeClient client;

    public OrderService(FlowForgeClient client) {
        this.client = client;
    }

    public Mono<ValidationResult> processOrder(String orderId) {
        // Now it returns ValidationResult because it's the last task in the plan
        return client.executeResult("order-process", orderId)
                     .cast(ValidationResult.class);
    }
}

[!IMPORTANT] Type Safety: If you tried to connect a task returning a String to another expecting an Integer, FlowForge will fail during startup, warning you of the mistake before it reaches production.

[!TIP] Check the Code: You can see the full source code for this level in our Sample Repository using the tag:

git checkout level-2

Next Level: Divide and Conquer (Parallelism) >>