Simplify Order Processing with Strategy Pattern and Custom Annotations in Java

We illustrate a typical order‑processing requirement where different order types need distinct handling.

First, the order entity and service interface are shown.

Traditional implementation uses a long chain of if‑else statements.

Using the Strategy pattern, the same logic can be reduced to two lines.

A custom annotation @HandlerType marks each concrete handler, and an abstract class AbstractHandler defines the common processing contract.

Each handler is registered as a Spring bean with @Component and the custom annotation.

At startup, a ClassScanner scans the specified package for classes annotated with @HandlerType, builds a map of order type to handler class, and injects it into HandlerContext via a HandlerProcessor that implements BeanFactoryPostProcessor.

The HandlerContext retrieves the appropriate handler bean from the Spring container using a utility BeanTool.

With this approach, adding a new order type only requires creating a new handler class; no changes to the existing service implementation are needed.

Full source code is available at the provided GitHub link.