Lesson 4 Complete Solution

This folder contains the complete solution for Lesson 4: HelloWorkflow - your first Temporal workflow and activity.

What's Included

Workflow Components

workflow/HelloWorkflow.kt - Workflow interface with @WorkflowInterface
workflow/HelloWorkflowImpl.kt - Workflow implementation that orchestrates the activity

Activity Components

activity/GreetingActivity.kt - Activity interface with @ActivityInterface
activity/GreetingActivityImpl.kt - Activity implementation with actual business logic

Configuration & Infrastructure

config/TemporalConfig.kt - Complete Temporal setup with worker registration
runner/HelloWorkflowRunner.kt - CommandLineRunner that executes the workflow
TemporalBootcampApplication.kt - Spring Boot main class

How It Works

Spring Boot starts and initializes Temporal configuration
Worker starts and registers HelloWorkflow and GreetingActivity
HelloWorkflowRunner executes automatically via CommandLineRunner
Workflow stub is created with proper task queue and workflow ID
Workflow executes and calls the GreetingActivity
Activity generates a greeting message
Result is returned and logged to console

Running This Solution

Start Temporal server:
```
temporal server start-dev
```
Run the application

Expected Output:

✅ Temporal worker started successfully for HelloWorkflow!
   Task Queue: lesson4-hello-queue
   Registered: HelloWorkflow, GreetingActivity
🚀 Running HelloWorkflow...
✅ Workflow completed!
   Result: Hello, Temporal Learner! Welcome to Temporal workflows!
🌐 Check the Temporal Web UI at http://localhost:8233

Verification

In the Console

You should see successful workflow execution with the greeting message.

In Temporal Web UI (http://localhost:8233)

Workflows tab - Shows your workflow execution
Task Queues tab - Shows lesson4-hello-queue with 1 worker
Workers tab - Shows your worker with registered capabilities

Workflow Details in Web UI

Workflow ID: hello-workflow-{timestamp}
Status: Completed
Execution timeline showing workflow and activity execution

Key Learning Points

Workflow vs Activity

Workflow (HelloWorkflowImpl): Orchestration logic, deterministic, can be replayed
Activity (GreetingActivityImpl): Business logic, can fail and retry, handles external calls

Annotations

@WorkflowInterface / @WorkflowMethod - Define workflow contracts
@ActivityInterface / @ActivityMethod - Define activity contracts
@Component - Spring manages activity as a bean

Configuration

Task Queue: Named channel connecting workflow requests to workers
Activity Options: Timeouts and retry policies
Worker Registration: Must register both workflows and activities

Execution Flow

Client creates workflow stub
Client calls workflow method
Temporal routes to appropriate worker
Worker executes workflow code
Workflow calls activity via stub
Worker executes activity code
Results flow back through the chain

Next Steps

Now that you understand the basic workflow and activity pattern, you're ready for more advanced concepts in the remaining lessons!

Lesson 4 Solution