Java Technologies - Lab 3

Dependency Injection and Cross-Cutting Concerns

Compulsory (1p)

• Create a simple, illustrative scenario that demonstrates all major types of dependency injection points in Spring Boot.
• Your example must also prove the order in which injection is performed: constructor → field → setter & method.

Homework (2p)

Create a Spring Boot Order Management System that handles Customers, Orders, and Discounts. Different clients (companies using your system) require different discount policies:

• Loyal customers get a percentage discount;
• Orders with a large value get a fixed amount discount;
• No discount (default).

• Define the domain model: Customer, Order, DiscountService and a simple in-memory repository of customers.
• Create the implementations for the discount policies.
• Use Spring Profiles or a custom configuration property to decide which discount strategy to inject.
• Create the OrderService which applies discounts using the injected DiscountService.
• Every time a discount is applied, log the method name, customer name, and discount amount.
• Create a decorator (using aspects) that, before applying a discount, checks if the customer exists and is eligible to get a discount. If not, throw a custom exception.
• Publish an event whenever a discount exceeds a certain amount and implement a listeners for that type of event.

Advanced (2p)

• Consider the case when you have decision-heavy logic that could grow or change frequently.
  Use a rule-engine, such as Drools (or define your own) to keep your code clean, maintainable, and easier to adapt to new business requirements.
  Implement the discount policies using the rule-engine.
• Create a reusable Spring Boot Starter that auto-configures an auditing aspect.