Feat/idr rate aggregator ahmad

[ahmad-shiddiqi]

Architectural Rationale

Polymorphism Justification (Strategy Pattern)

The application exposes a single multi-resource endpoint that serves different financial data types. Instead of implementing conditional logic (e.g., if-else or switch) inside the service layer, the Strategy Pattern is used.

Each resource type implements a common IDRDataFetcher interface. This design:

• Adheres to the Open/Closed Principle
• Allows new resource types to be added without modifying existing logic
• Keeps the service layer clean and focused
• Improves maintainability and testability

This approach scales better than a conditional block, which would grow increasingly complex as new resource types are introduced.

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Client Factory (FactoryBean)

A FactoryBean is used to construct the external API client.

The FactoryBean:

• Encapsulates client construction logic
• Centralizes WebClient configuration
• Allows future enhancements such as interceptors, timeouts, retries, or authentication
• Decouples client configuration from business components

While a simple @Bean method could create the client, the FactoryBean approach provides greater flexibility and better separation of concerns for external integrations.

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Startup Runner Choice (ApplicationRunner)

ApplicationRunner is used for initial data ingestion instead of @PostConstruct.

This is preferred because:

• It runs after the full Spring context is initialized
• It clearly separates lifecycle execution from bean initialization
• It provides better control over startup sequencing
• It aligns better with production-grade startup handling

Using @PostConstruct would mix initialization logic with bean lifecycle concerns and provides less explicit control over execution timing.

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