Business logic in services in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Spring Boot service method?

Consider this service method that calculates a discount based on customer type:

public double calculateDiscount(String customerType, double amount) {
    if ("VIP".equals(customerType)) {
        return amount * 0.2;
    } else if ("Regular".equals(customerType)) {
        return amount * 0.1;
    } else {
        return 0;
    }
}

What will calculateDiscount("VIP", 1000) return?

A 0.0

B 100.0

C 200.0

D Throws NullPointerException

💡 Hint

Check the condition for the "VIP" customer type and the multiplication.

The method returns 20% of the amount for "VIP" customers, so 1000 * 0.2 = 200.0.

❓ state_output

intermediate

What is the state of the order after calling this service method?

Given this service method that updates an order status:

public void processOrder(Order order) {
    if (order.getItems().isEmpty()) {
        order.setStatus("FAILED");
    } else {
        order.setStatus("PROCESSED");
    }
}

If order.getItems() returns an empty list, what will be the order status after processOrder(order)?

A "PROCESSED"

B "PENDING"

C null

D "FAILED"

💡 Hint

Think about what happens when the items list is empty.

The method sets the status to "FAILED" if the items list is empty.

📝 Syntax

advanced

Which option correctly implements a transactional service method?

Choose the correct way to annotate a Spring Boot service method to ensure it runs within a transaction:

A

@Transactional
public void updateInventory() { /* code */ }

B

@Transaction
public void updateInventory() { /* code */ }

C

@Transactional(readOnly = true)
public void updateInventory() { /* code */ }

D

@Transactional(propagation = Propagation.NEVER)
public void updateInventory() { /* code */ }

💡 Hint

Look for the correct annotation spelling and usage for a writable transaction.

@Transactional is the correct annotation. Option A is misspelled. Option A marks the transaction as read-only, which is not suitable for updates. Option A disables transactions.

🔧 Debug

advanced

Why does this service method throw a NullPointerException?

Examine this service method:

public double calculateTotal(Order order) {
    return order.getItems().stream()
        .mapToDouble(item -> item.getPrice() * item.getQuantity())
        .sum();
}

Sometimes this method throws a NullPointerException. What is the most likely cause?

A The getItems() method returns null instead of an empty list.

B The order object is null when passed to the method.

C The item price or quantity is null causing the exception.

D The stream() method is not supported on the items list.

💡 Hint

Consider what happens if getItems() returns null and you call stream() on it.

If getItems() returns null, calling stream() on null causes NullPointerException. The order object itself being null would cause a different error earlier. Item price and quantity are primitives or boxed types but unlikely to cause NPE here. The stream() method is supported on collections.

🧠 Conceptual

expert

Which statement best describes the role of services in Spring Boot architecture?

In a typical Spring Boot application, what is the main purpose of the service layer?

A To handle HTTP requests and responses directly.

B To contain business logic and coordinate data operations between controllers and repositories.

C To manage database connections and execute SQL queries.

D To render HTML views and manage user interface components.

💡 Hint

Think about where the business rules and logic should live in the app.

The service layer contains business logic and acts as a bridge between controllers (which handle HTTP) and repositories (which handle data storage). Controllers do not contain business logic, repositories do not contain business rules, and views handle UI.