Spring Boot Teaching Template for Frontend Developers

Welcome, developer! 👋 This project is a learning platform for frontend devs who want to understand the Java + Spring ecosystem — through code, not slides.

✅ What you'll find

• ✅ A working feature: Todo

  • TodoController, TodoService, TodoRepository, Todo model
  • Uses MongoDB for persistence with Testcontainers for testing
  • Demonstrates Dependency Injection (DI) using constructor injection
  • Has Swagger UI docs via springdoc-openapi

• 🧠 Learning-oriented JavaDocs with links to Spring resources

• 🧪 ArchUnit tests to enforce clean architecture

• 🔍 Functional tests to validate feature behavior using Testcontainers

🏗 Architecture

This project implements Vertical Slice Architecture (VSA), organizing code around features rather than technical layers. You can explore this through the Todo feature implementation.

Why VSA?

• 🎯 Feature-focused organization
• 🔄 Independent, full-stack slices
• 🚀 Faster development cycles
• 🛠 Easier maintenance

Learn more about VSA:

• Baeldung: Vertical Slice Architecture in Java
• Exploring Software Architecture: Vertical Slice

🎯 Todo Feature Showcase

The Todo feature demonstrates VSA principles in action:

• Complete vertical slice from API to persistence
• Self-contained in features/todo package
• Includes dedicated tests and documentation
• Shows proper dependency management

🚀 Run the app

1. Make sure you have:

   • Java 21
   • Docker running

2. Start MongoDB:

docker run -d --name mongodb -p 27017:27017 mongo:latest

3. Start the app:

./gradlew bootRun

Open Swagger docs: http://localhost:8080/swagger-ui.html

📚 Learning Tasks

Task 1: Create the "Greeting" Feature

Your task is to build a new Spring feature called greeting, and connect it to the existing todo feature.

---

🎯 Objective

Create a REST endpoint /api/greeting that returns a message like: "Hello from Spring! You have 3 open tasks."

This feature should use the existing TodoService via constructor-based Dependency Injection.

---

🛠 Steps

1. Create a new package:
   lv.ctco.springboottemplate.features.greeting

2. Implement GreetingService

• Inject TodoService using constructor-based DI
• Use todoService.getAllTodos() and count how many are not completed
• Return a string like: "Hello from Spring! You have X open tasks."

3. Create GreetingController

• Map it to /api/greeting
• Delegate to GreetingService

4. Follow naming conventions

• Class names must end with Service, Controller, etc.
• Use annotations like @Service, @RestController, @RequestMapping

---

🧪 Test Yourself

We've prepared tests to verify your work:

✅ ArchUnit tests will prevent you from structure issues

✅ GreetingServiceIntegrationTest.java
📍 Location: src/test/java/lv/ctco/springboottemplate/features/greeting/
🔒 Also @Disabled. Remove to test your endpoint.

If All tests pass and the greeting appears at /api/greeting, you've completed the task!

---

💡 Hints

• Constructor injection is preferred over @Autowired
• Use Java Streams to filter open todos
• The TodoService is already a Spring bean — you can inject it!

---

✅ Done?

When both tests are green and the endpoint works, congratulations!
You've created a feature using Spring idioms and learned how features interact via Dependency Injection.

🔥 Welcome to the backend side.

Task 2: Create the "Statistics" Feature

🎯 Objective

Create a REST endpoint /api/statistics that provides insights about Todo items.

📋 Requirements

1. API Endpoint

• Base path: /api/statistics
• Support query parameters:
  • from - Start date (e.g., 2023-01-01)
  • to - End date (e.g., 2023-12-31)
  • format - Response format (summary or detailed)

2. Statistics to Include

• Total number of todos
• Number of completed todos
• Number of pending todos
• Todos per user breakdown

3. Technical Requirements

• Use MongoDB aggregations for efficient data processing
• Create DTOs for API responses
• Implement proper error handling
• Follow existing architectural patterns
• Test code with unit and integration tests

4. Summary Sample Response

{
  "totalTodos": 10,
  "completedTodos": 7,
  "pendingTodos": 3,
  "userStats": {
    "user1": 5,
    "user2": 3,
    "user3": 2
  }
}

5. Detailed Sample Response

{
  "totalTodos": 10,
  "completedTodos": 7,
  "pendingTodos": 3,
  "userStats": {
    "user1": 5,
    "user2": 3,
    "user3": 2
  },
  "todos": {
    "completed": [
      {
        "id": "1",
        "title": "Deploy to production",
        "createdBy": "user1",
        "createdAt": "2024-03-15T10:30:00Z",
        "completedAt": "2024-03-15T14:20:00Z"
      },
      // ... more completed todos
    ],
    "pending": [
      {
        "id": "8",
        "title": "Review pull request",
        "createdBy": "user2",
        "createdAt": "2024-03-15T09:00:00Z"
      },
      // ... more pending todos
    ]
  }
}