🚀 Week 5: Spring Boot – Building Your First Backend Application

Welcome to Week 5! This is a major milestone in your backend development journey. Until now, you have built a strong foundation in core Java concepts, collections, IO, threading, and design patterns.

This week, you will transition into real-world backend development using Spring Boot — one of the most widely used frameworks for building production-grade Java applications.

🎯 Learning Objectives

By the end of this week, you will be able to:

  • Understand what Spring and Spring Boot are
  • Explain Inversion of Control (IoC) and Dependency Injection (DI)
  • Build REST APIs using Spring Boot
  • Structure applications using Controller, Service, and Repository layers
  • Handle HTTP requests (GET, POST, PUT, DELETE)
  • Use configuration via application.properties
  • Test APIs using tools like Postman or curl

🧠 Why Spring Boot?

In real-world backend systems:

  • Applications must be scalable
  • Code must be modular and maintainable
  • Dependency management should be automated
  • Boilerplate code should be minimized

Spring Boot solves these problems by:

  • Providing auto-configuration
  • Reducing setup complexity
  • Enabling rapid development of REST APIs
  • Promoting best practices and layered architecture

🏗 What You Will Build This Week

You will convert your previous Java-based system into a Spring Boot REST API.

Example Project:

Expense Tracker Backend (Recommended)

Features you will implement:

  • Create expense
  • Get all expenses
  • Get expense by ID
  • Update expense
  • Delete expense

📦 Key Concepts Covered

This week focuses on the following core backend concepts:

🔹 Spring Fundamentals

  • What is Spring Framework?
  • What is Spring Boot?
  • IoC Container
  • Dependency Injection

🔹 Spring Boot Basics

  • Spring Boot project setup
  • Starter dependencies
  • Auto-configuration

🔹 REST API Development

  • @RestController
  • @RequestMapping
  • @GetMapping, @PostMapping, @PutMapping, @DeleteMapping
  • Request & Response handling

🔹 Layered Architecture

  • Controller Layer (API layer)
  • Service Layer (Business logic)
  • Repository Layer (Data access – intro only, DB comes next week)

📁 Week Structure

This week is structured as follows:

  • 📘 study-material.md → Concepts and explanations
  • 💻 exercises.md → Hands-on coding tasks
  • 🧠 quiz.md → Concept validation
  • 🛠 assignment.md → Build a real REST API
  • 📊 assessment.md → Evaluate your understanding
  • ✅ solutions.md → Reference implementations
  • 🔍 review-checklist.md → Code review guide

🧪 Testing Focus This Week

As someone transitioning from testing to development, this is your strength.

You are expected to:

  • Test APIs using Postman or curl
  • Validate response correctness

  • Think about edge cases:

    • Invalid input
    • Missing fields
    • Incorrect IDs
  • Observe HTTP status codes

⚙️ Tools Required

Make sure you have the following installed:

  • Java (JDK 17 or above)
  • Maven or Gradle
  • IDE (IntelliJ IDEA recommended)
  • Postman (or curl)
  • Git

⏱ Expected Effort

  • Study: 6–8 hours
  • Coding Practice: 6–8 hours
  • Assignment: 4–6 hours

📌 Deliverables

By the end of this week, you should:

  • Have a working Spring Boot application
  • Implement at least 4 REST endpoints
  • Follow proper layered architecture
  • Push your code to GitHub
  • Be ready for code review

🧠 Mentor Notes

Focus on:

  • Understanding why DI is used, not just how
  • Writing clean and readable code
  • Keeping methods small and focused
  • Following naming conventions

Avoid:

  • Writing everything in one class
  • Skipping error handling
  • Copy-pasting without understanding

🚀 What’s Next?

Next week, you will:

➡️ Connect your application to a database ➡️ Learn JPA & Hibernate ➡️ Persist real data

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