💻 Exercises – Week 5: Spring Boot

These exercises are designed to help you build confidence step-by-step in developing backend applications using Spring Boot.

👉 Complete all exercises in order. Do not skip.

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🎯 Goal

By completing these exercises, you will:

• Understand Spring Boot project setup
• Build REST APIs
• Apply layered architecture
• Use Dependency Injection properly
• Think like a backend developer

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🧩 Exercise 1: Create Your First Spring Boot Project

Task

• Create a Spring Boot project using:

  • Spring Initializr
  • Maven or Gradle

• Add dependency:

  • Spring Web

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Expected Output

• Project runs successfully
• Application starts on port 8080
• No errors

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🧩 Exercise 2: Create a Simple REST Endpoint

Task

Create a controller:

@RestController
public class HelloController {

    @GetMapping("/hello")
    public String hello() {
        return "Hello Backend!";
    }
}

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Test

Open browser or use curl:

http://localhost:8080/hello

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Expected Output

Hello Backend!

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🧩 Exercise 3: Build Expense Controller

Task

Create a controller:

• Endpoint: /expenses
• Method: GET
• Return: List of expenses (hardcoded for now)

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Example

@GetMapping("/expenses")
public List<String> getExpenses() {
    return List.of("Food", "Travel", "Shopping");
}

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🧩 Exercise 4: Add Path Variable

Task

Create API:

GET /expenses/{id}

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Example

@GetMapping("/expenses/{id}")
public String getExpense(@PathVariable int id) {
    return "Expense ID: " + id;
}

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🧩 Exercise 5: Add POST API

Task

Create API:

POST /expenses

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Example

@PostMapping("/expenses")
public String createExpense() {
    return "Expense Created";
}

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🧩 Exercise 6: Introduce Service Layer

Task

• Create ExpenseService class
• Move logic from controller to service

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Example

@Service
public class ExpenseService {

    public List<String> getExpenses() {
        return List.of("Food", "Travel");
    }
}

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Update Controller

@RestController
public class ExpenseController {

    private final ExpenseService service;

    public ExpenseController(ExpenseService service) {
        this.service = service;
    }

    @GetMapping("/expenses")
    public List<String> getExpenses() {
        return service.getExpenses();
    }
}

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🧩 Exercise 7: Add PUT and DELETE APIs

Task

Create:

• PUT /expenses/{id}
• DELETE /expenses/{id}

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Expected Behavior

• Update returns confirmation message
• Delete returns confirmation message

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🧩 Exercise 8: Use Request Body

Task

Accept input using request body.

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Example

@PostMapping("/expenses")
public String createExpense(@RequestBody String expense) {
    return "Created: " + expense;
}

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🧩 Exercise 9: Add Model Class

Task

Create a model:

public class Expense {
    private int id;
    private String name;
    private double amount;
}

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Update APIs to use this object instead of String.

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🧩 Exercise 10: Add Configuration

Task

Modify:

application.properties

Add:

server.port=8081
spring.application.name=expense-tracker

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Verify

• Application runs on new port
• Name is visible in logs

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🧪 Exercise 11: API Testing

Task

Test all APIs using:

• Postman OR
• curl

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Validate

• Correct responses
• Proper status codes
• Invalid input handling

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🧠 Bonus Challenge (Optional)

🔥 Build Mini Expense API

Implement:

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

Use:

• Controller
• Service
• Model

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⚠️ Rules

• Do NOT write all logic in controller
• Follow clean code practices
• Use meaningful names
• Keep methods small

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🏁 Completion Checklist

✔ Spring Boot app created ✔ REST APIs implemented ✔ Service layer added ✔ Dependency Injection used ✔ APIs tested successfully

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🚀 Next Step

After completing exercises:

➡️ Move to Assignment for real-world implementation

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