Capstone Project: Expense Tracker Backend (Introduction & Architecture)

1. Why Expense Tracker?

An Expense Tracker is a real-world, business-relevant application.

It demonstrates:

• Clean backend architecture
• Secure API design
• Practical database modeling
• Meaningful business logic

This project is: ✔ Interview-friendly
✔ Extendable
✔ Production-oriented

Many companies build similar internal systems.

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2. What We Are Building

A backend system that allows users to:

• Register and login securely
• Track daily expenses
• Categorize expenses
• View expense summaries
• Secure data per user

This backend can later support:

• Mobile apps
• Web dashboards
• Analytics tools

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3. Core Features

Authentication & Users

• User registration
• User login (JWT-based)
• Role-based access (USER, ADMIN)

Expense Management

• Add expense
• Update expense
• Delete expense
• View expenses

Categories

• Create categories (Food, Travel, Rent, etc.)
• Assign category to expense

Reports (Phase-wise)

• Monthly expense summary
• Category-wise totals

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4. Non-Functional Requirements

✔ RESTful APIs
✔ Input validation
✔ Global exception handling
✔ Clean layered architecture
✔ Secure endpoints
✔ Externalized configuration
✔ Logging & monitoring
✔ Docker-ready

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5. Tech Stack

Layer	Technology
Language	Java 17
Framework	Spring Boot 3
Security	Spring Security + JWT
Database	H2 (dev), PostgreSQL/MySQL (prod)
ORM	Spring Data JPA
Docs	Swagger / OpenAPI
Build	Maven
Container	Docker

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6. High-Level Architecture

Client
  |
  v
Controller (REST APIs)
  |
  v
Service (Business Logic)
  |
  v
Repository (JPA)
  |
  v
Database

Security, validation, logging, and caching are applied across layers.

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7. Package Structure

com.example.expensetracker
 ├── config          # Configuration classes
 ├── controller      # REST controllers
 ├── dto             # Request & response DTOs
 ├── entity          # JPA entities
 ├── exception       # Custom exceptions & handlers
 ├── repository      # JPA repositories
 ├── security        # JWT & security config
 ├── service         # Business logic
 └── ExpenseTrackerApplication.java

This structure is enterprise-safe and interview-safe.

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8. Development Phases

Phase 1: Foundation

• Project setup
• Dependencies
• Basic run

Phase 2: User & Auth

• User entity
• Registration & login
• JWT security

Phase 3: Expense Module

• Expense entity
• CRUD APIs
• Category mapping

Phase 4: Quality & Production

• Validation
• Exception handling
• Logging & caching
• Swagger
• Docker

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9. How You Should Work on This Project

✔ One feature at a time
✔ Commit after each milestone
✔ Write clean method names
✔ Think like a backend engineer

This project is meant to be: slow, solid, and practical.

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10. What You Should Do Now

Before moving ahead:

1. Create a new Git repository
   Suggested name:

   expense-tracker-backend
   

2. Keep this repo separate from practice code
3. Use meaningful commit messages

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11. What’s Next?

➡ Capstone – Article 1: Project Setup & Dependency Selection

• Create Spring Boot project
• Select correct dependencies
• Initial application run

Type Next when you’re ready to start coding 🚀