Practicing Service Modularization in Java 9

1. What is Modularization?

Modularization involves breaking systems into independent, interconnected modules with standardized interfaces. In Java, this concept extends beyond packages to formal module definitions with explicit dependencies and access controls.

2. Why Modularization?

Key benefits include independent module testing/deployment, easier upgrades via versioning, and reduced maintenance costs through clear service boundaries. The article demonstrates these advantages through a practical multi-module project.

3. Implementation Principles

Java 9 modules use module-info.class files to define module names, dependencies, and exported APIs. The module system replaces the traditional parent-child classloader model with a more controlled approach that restricts class access based on module relationships.

4. Practical Example

The article walks through building a modular project with four components (eat, transportation, work, console), showing how to define module dependencies, export APIs, and handle reflective access using opens and transitive keywords.

5. Benefits Summary

Modularization improves code readability, reduces circular dependencies, enables secure reflective access control, and allows need-based packaging. The example project demonstrates creating a lightweight 35.9MB JRE environment from modular components.