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Java Modules

Usage examples of modules in Java version > 8

Modules Java 9 modules enhance the platform as follows:

• Strong encapsulation. Encapsulation is honored during compilation and execution, even in the face of reflection attempts.
• Reliable configuration. The runtime checks the availability of dependencies before launching the application.
• Creation of images that packages the application with a custom-made Java platform. This implies:
  • Lower memory and disk requirements (useful for microservices and small devices)
  • Greater security, because the code involved is less.
  • Improved optimization (dead-code elimination, constant folding, compression, etc.).
  • Decoupled services without classpath scanning (interface implementations are explicitly indicated).
  • Fast type loading. The system knows where each package is without having to scan the classpath.
  • Preserves the borders established by architecture.

Strong encapsulation has other benefits, such as the ability to test a module in isolation, avoid code decay by introducing accidental dependencies, and dependency reduction when multiple teams work in parallel.

A module in Java is an artifact that can contain code, resources, and metadata. The metadata describes dependencies with other modules, and regulates access to the module's packages.

Example of a module file

// nombre del módulo. open permite la reflexión en todo el módulo
open module com.ejemplo
{
// exporta un paquete para que otros módulos accedan a sus paquetes públicos
exports com.apple;
// indica una dependencia con el módulo com.orange
requires com.orange;
// indica una dependencia con com.banana. el 'static' hace que la dependencia
// sea obligatoria durante compilación pero opcional durante ejecución
requires static com.banana;
// indica una dependencia al módulo com.berry y sus dependencias
requires transitive com.berry;
// permite reflexión en el módulo com.pear
opens com.pear;
// permite reflexión en el paquete com.lemon pero solo desde el módulo com.mango
opens com.lemon to com.mango;
// expone el tipo MyImplementation que implementa el servicio MyService
provides com.service.MyService with com.consumer.MyImplementation;
// usa el servicio com.service.MyService
uses com.service.MyService;
}

More info https://www.adictosaltrabajo.com/2017/10/30/modularidad-en-java-9-12/