Projects: Kotlin — Backend Web, Spring Boot, and Android Development¶

Project ideas ranging from beginner to expert. Build real things — not toy examples. Each project integrates multiple modules and produces a deployable artifact.

Table of Contents¶

• Beginner Projects (Modules 01–02)
• Intermediate Projects (Modules 03–05)
• Advanced Projects (Modules 06–10)
• Expert Projects (Modules 11–12)

Beginner Projects (Modules 01–02)¶

Project 1: Command-Line Task Manager¶

Description: A command-line to-do list app that stores tasks in a JSON file. Users can add, list, complete, and delete tasks.

Skills required: Kotlin basics (Module 01), data classes, sealed classes, file I/O (Module 02)

Acceptance criteria: - ./tasks add "Buy groceries" appends a task - ./tasks list prints all tasks with status - ./tasks done 1 marks task #1 complete - Tasks persist between runs (JSON file) - Proper error handling when task ID doesn't exist

Extension ideas: Add due dates, priorities, or filtering by status.

Project 2: Currency Converter CLI¶

Description: A command-line tool that converts between currencies using hardcoded exchange rates (no external API needed). Demonstrates Kotlin data classes, operator overloading, and string templates.

Skills required: Kotlin basics (Module 01), data classes (Module 02)

Acceptance criteria: - Define a Money(amount: BigDecimal, currency: Currency) data class - Support +, -, and conversion between at least 5 currencies - Clean output with proper decimal formatting - Handles invalid currency codes gracefully

Intermediate Projects (Modules 03–05)¶

Project 3: Async File Processor¶

Description: A command-line tool that processes a directory of CSV files concurrently using coroutines. Computes statistics (sum, average, min, max) per column and outputs a summary report.

Skills required: Kotlin coroutines (Module 03), file I/O, extension functions

Acceptance criteria: - Process each file in a separate coroutine using async/await - Combine results without blocking threads - Handle malformed CSV rows gracefully - Demonstrate measurable concurrency speedup vs sequential processing

Project 4: Product Catalog REST API¶

Description: A Spring Boot REST API for managing a product catalog. Supports CRUD operations on products and categories.

Skills required: Spring Boot (Module 04), Spring Data JPA + PostgreSQL (Module 05)

Acceptance criteria: - GET /products returns paginated list - POST /products creates a product - GET /products/{id} returns a single product - PUT /products/{id} updates a product - DELETE /products/{id} soft-deletes a product - Products belong to categories; GET /categories/{id}/products works - Uses Spring Data JPA with a real PostgreSQL database

Advanced Projects (Modules 06–10)¶

Project 5: Authenticated Note-Taking API¶

Description: A REST API for personal notes with JWT authentication. Each user has their own notes; no user can see another user's notes.

Skills required: Spring Boot (Module 04), Spring Data (Module 05), Spring Security + JWT (Module 06)

Acceptance criteria: - POST /auth/register creates an account - POST /auth/login returns a JWT - All /notes endpoints require a valid JWT - Notes are scoped to the authenticated user - Refresh token mechanism (access token expires in 15 minutes) - Comprehensive integration tests

Project 6: Android Weather App¶

Description: An Android app that shows current weather for the user's location and allows searching by city name. Uses a free weather API (such as Open-Meteo, which requires no API key).

Skills required: Android fundamentals (Module 09), Android advanced — Retrofit, ViewModel, StateFlow (Module 10)

Acceptance criteria: - Jetpack Compose UI with Material3 design - Location permission request handled correctly - Current conditions and 7-day forecast - City search with debouncing - Offline cache (show last known data when no network) - Handle loading, success, and error states with proper UI feedback

Expert Projects (Modules 11–12)¶

Project 7: Event-Driven Order Processing System¶

Description: A distributed order processing system using Spring Boot microservices and Kafka. Service A accepts orders via REST; Service B processes payments via Kafka events; Service C sends confirmation emails (simulated).

Skills required: Spring Boot (Module 04), Spring Data (Module 05), Spring Advanced — Kafka (Module 07), Testing (Module 11)

Acceptance criteria: - Three Spring Boot services communicating via Kafka topics - Eventual consistency: order transitions through PENDING → PAID → CONFIRMED states - At-least-once delivery with idempotent consumers - TestContainers-based integration tests for Kafka flows - Actuator health endpoints on all services - Docker Compose file to run the full system locally

Project 8: Full-Stack Kotlin App (Capstone Preview)¶

Description: A Spring Boot backend API + Android app that share a Kotlin Multiplatform model library. See Module 12 (Capstone) for the full specification.

Skills required: All modules

This project is the Module 12 capstone. See modules/12_capstone-project/README.md for the full brief.

My Projects¶

Track your own projects here. Append rows; never delete.