🛠 Assignment – Week 5: Spring Boot REST API

This assignment is designed to help you apply everything you have learned this week in a real-world backend development scenario.

You will build a mini backend application using Spring Boot following proper architecture and best practices.

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🎯 Objective

Build a RESTful Expense Tracker API with:

• Clean layered architecture
• Proper use of Spring Boot annotations
• Dependency Injection
• REST endpoints for CRUD operations

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🧩 Problem Statement

You are required to develop a backend system for managing expenses.

Each expense should contain:

• id (integer)
• name (string)
• amount (double)

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📦 Functional Requirements

Implement the following APIs:

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1️⃣ Create Expense

POST /expenses

• Accept expense in request body
• Return created expense

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2️⃣ Get All Expenses

GET /expenses

• Return list of all expenses

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3️⃣ Get Expense by ID

GET /expenses/{id}

• Return specific expense
• Handle case when expense is not found

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4️⃣ Update Expense

PUT /expenses/{id}

• Update expense details
• Return updated response

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5️⃣ Delete Expense

DELETE /expenses/{id}

• Delete expense
• Return confirmation message

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🏗 Architecture Requirements

Your application must follow:

🔹 Controller Layer

• Handles HTTP requests
• Should NOT contain business logic

🔹 Service Layer

• Contains business logic
• Handles data operations

🔹 Model Layer

• Represents Expense object

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⚙️ Technical Requirements

• Use Spring Boot
• Use @RestController, @Service
• Use Dependency Injection
• Use proper request mappings
• Use application.properties

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🧪 Testing Requirements

You must test your APIs using:

• Postman OR
• curl

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Validate:

• Correct responses
• Proper HTTP status codes

• Edge cases:

  • Invalid ID
  • Empty input
  • Duplicate data

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📁 Suggested Project Structure

com.example.expensetracker
│
├── controller/
├── service/
├── model/
└── Application.java

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📌 Constraints

• No database required (use in-memory list)
• No UI required
• Focus on backend logic

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📊 Evaluation Criteria

Category	Marks
API Functionality	20
Code Structure	20
Use of DI	15
Clean Code	15
Testing	15
Edge Case Handling	15
Total	100

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🧠 Hints

• Start with model class
• Then create service layer
• Then controller
• Test each API step-by-step
• Use meaningful names

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⚠️ Common Mistakes to Avoid

• Writing logic in controller
• Not using DI
• Hardcoding values
• Ignoring invalid inputs
• Not testing APIs

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🚀 Bonus (Optional)

If you finish early, try:

• Return proper HTTP status codes
• Add basic validation
• Add logging
• Improve response structure

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📤 Submission

• Push code to GitHub repository
• Ensure code compiles and runs
• Be ready to explain your code

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🏁 Expected Outcome

By completing this assignment, you will:

• Build your first real backend API
• Understand Spring Boot flow
• Gain confidence in REST development
• Be ready for database integration (next week)

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