Design and Refactoring of a Rule Engine for User Application Processing

Recently a small requirement arose to extend the existing trial user application rules, requiring a rule engine that can evaluate conditions combined with AND or OR logic and support short‑circuit evaluation to skip further processing when a condition fails.

The author outlines the current situation, noting that while a quick modification could meet the immediate need, it would lead to poor maintainability, prompting a decision to refactor the rule execution component.

The proposed design introduces a Rule Engine (V1) that separates rules, data, and the executor, allowing each rule to be independent. A Rule template class defines a convert method for parameter conversion, enabling extensibility for rule‑specific data.

Key steps include abstracting rules, constructing the executor, and invoking it within the application flow. Diagrams illustrate the rule abstraction, executor construction, and execution process.

Advantages of this design are its simplicity, modularity, and clear separation of concerns, making the calling code tidy and allowing easy extension via the convert method.

However, the design has drawbacks: rules may have data dependencies, and modifying a shared DTO directly can be problematic; the author recommends pre‑building data structures to avoid such issues.

Overall, the refactored rule engine provides a cleaner architecture with short‑circuit capabilities, but careful handling of data dependencies is required for robust long‑term maintenance.