💰 Expense Tracker

Expense Tracker is a full-stack web application designed to help users manage personal or business finances. Built with Java 17, Spring Boot, and Angular, the app allows users to track expenses, categorize them, set budgets, and generate summaries. It also includes real-time notifications via WebSocket when users exceed their budgets.

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🚀 Features

• 🔐 User Authentication with Spring Security (JWT)
• ➕ Add, Edit, Delete expenses
• 📊 View expenses by:
  • Category
  • Date range
  • Monthly summaries
• 💡 Budget tracking and overspending warnings
• 📂 Expense categorization
• 📈 Summary reports by month and category
• 🔎 Filtering and sorting by date, amount, and category
• 📢 Real-time notifications via WebSocket when budget limits are exceeded

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🧩 Tech Stack

Backend

• Java 17
• Spring Boot
• Spring Security + JWT
• Spring WebSocket (STOMP)
• Java Streams & Lambdas
• JPA for database access

Frontend

• Angular
• TypeScript
• Angular Router, Forms
• REST API with HttpClient
• WebSocket client (SockJS + STOMP) for push notifications

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🧠 Concepts & Topics Used

This project reinforces both core and advanced Java/backend concepts, including areas often covered in Oracle certification:

✅ Core Java

• OOP: encapsulation, inheritance, polymorphism
• Collections Framework: List, Map, Set
• Exception Handling:
  • Checked/unchecked exceptions
  • Custom exceptions (InvalidExpenseException)
• Java I/O (optional for file storage)
• Date/Time API

✅ Advanced Java

• Streams & Lambdas for:
  • Filtering by category/date/amount
  • Grouping and summarizing
• WebSocket (STOMP) for budget warning notifications

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📦 Functional Overview

1. Authentication

• POST /auth/register – Register
• POST /auth/login – Login and get JWT

JWT must be added to Authorization headers for all authenticated routes.

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2. Expense Management

• GET /expenses – Fetch expenses
• POST /expenses – Add new expense
• PUT /expenses/{id} – Edit expense
• DELETE /expenses/{id} – Delete expense

Each expense includes:

• amount
• category
• description
• date

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3. Budgeting & Summaries

• Set monthly budget
• Track remaining balance
• Summary by category and month
• WebSocket alert when budget is exceeded

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⚠️ Error Handling

Handled globally via @ControllerAdvice. Returns clear and consistent error responses.

Example:

{
  "timestamp": "2025-07-30T12:00:00Z",
  "status": 400,
  "error": "Bad Request",
  "message": "Invalid expense amount"
}