Converting Tightly Coupled Application into Loosely Coupled and Pluggable Modules - hmislk/hmis GitHub Wiki

Title:
Converting Tightly Coupled Application into Loosely Coupled and Pluggable Modules

Contents:

1. Introduction

Our current application is tightly coupled, with direct dependencies between modules, making it difficult to modify, extend, or reuse individual components. To improve flexibility, maintainability, and scalability, we plan to refactor the system into loosely coupled, pluggable modules.

2. Current Challenges

  • Direct dependencies between modules.
  • Changes in one module affect others.
  • Difficult to replace, upgrade, or remove modules.
  • Limited reusability and testability.

3. Objectives

  • Separate responsibilities into independent modules.
  • Ensure modules communicate through well-defined interfaces.
  • Enable dynamic loading, replacement, and removal of modules.
  • Reduce the impact of changes in one module on others.

4. Key Design Principles

  • Separation of Concerns: Each module handles a specific responsibility.
  • Interface-Based Design: Define interfaces for communication, not direct class dependencies.
  • Dependency Injection: Inject required services at runtime rather than hardcoding them.
  • Event-Driven Communication: Use events or messaging where appropriate to decouple interactions.
  • Service Registration: Maintain a registry for discovering and loading modules dynamically.

5. Implementation Steps

  • Identify existing modules and their responsibilities.
  • Define clear interfaces (APIs) for each module.
  • Extract modules into separate packages or libraries.
  • Replace direct calls with interface-based communication.
  • Introduce a plugin loader or module manager to handle pluggable modules.
  • Ensure proper error handling when a module is unavailable.
  • Test modules independently and as part of the whole system.

6. Technologies and Patterns

  • Java Service Provider Interface (SPI).
  • OSGi (for dynamic module loading).
  • Dependency Injection frameworks (like CDI or Spring).
  • Event buses (such as Guava EventBus).
  • Modular build tools (like Maven multi-module projects).

7. Expected Benefits

  • Easier maintenance and updates.
  • Independent development and testing of modules.
  • Improved scalability and flexibility.
  • Ability to add or remove features without affecting the core system.
  • Cleaner, more organised codebase.

8. Conclusion

Transitioning to loosely coupled, pluggable modules will future-proof our application by enhancing its adaptability and maintainability. Careful planning and gradual refactoring are essential to achieving a smooth migration.

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