System exception VS Business Exception

Overview

A business exception is different from a system error (like a NullPointerException). It represents a situation where a domain or business rule has been violated.

• For example, situations like “This user has already canceled their membership” or “There is not enough stock to complete the order” are not technical system failures ⇒ they are expected exceptions within the application’s business logic
• Exception handling

Aspect	System Exception	Business Exception
Meaning	A technical failure, programming mistake, or infrastructure problem.	A violation of an established business rule.
Examples	NullPointerException, IOException, database connection failure.	DuplicateOrderException, InvalidUserStateException, InsufficientFundsException.
Handling	The operation usually cannot be recovered. The error should be logged, and a generic failure response (e.g., 500 Internal ServerError) is sent.	The operation is stopped, and a specific, meaningful message is returned to the user (e.g., 409 Conflict, 400 Bad Request).
Origin	Often originates deep within a framework, library, or low-level code.	Originates in your application’s business service layer.

Business Exception

• location - service layer
• It’s standard practice to design business exceptions as unchecked exceptions by having them extend RuntimeException. This keeps your business logic clean from mandatory try-catch blocks.
• It’s a good idea to separate the exception messages used for internal logging from the messages shown to the end-user. The internal log can be very detailed for debugging, while the user message should be simple and clear.
• Use ⭐Custom Exceptions

Example - business exception

public class OrderService {
    public void placeOrder(String productId, int quantity) {
        Product product = productRepository.findById(productId);
 
        // Check the business rule: Is there enough stock?
        if (product.getStock() < quantity) {
            // If not, throw a specific business exception.
            throw new BusinessException(ErrorCode.OUT_OF_STOCK);
        }
 
        // ... continue with order logic if stock is sufficient.
    }
}