multi-module

Multi Module Example

This is an example of a multi-module project. It demonstrates the following:

• Module Inheritance
• Module Aggregation
• Distribution Management
• Dependency Management (including importing dependency management from other modules)
• Dependency Scopes

Project Structure

Module Artifact ID	Description	Dependencies
multi-module-parent	The parent pom
multi-module-api	API of the app's business
multi-module-core	Implementation of the API	multi-module-api (compile)
multi-module-app	The application	multi-module-api (compile) multi-module-core (runtime)

API

Contains a single HelloService interface

Core

Contains a single HelloServiceImpl class which implements HelloService and is annotated with the spring framework's @Service stereotype.

App

Contains a single Main class which creates the Spring application context and scans the application's package. It is then uses the HelloService to generate a "Hello " message and prints it to stdout.
This module has no access in compile time to the HelloServiceImpl class due to the runtime scope used for the dependency on the core module.

Running the Example

Note- All commands below shall be executed in the command line (bash) from the root of the project.

Build the Project

mvn clean install

This will build all 4 modules.

Run the Application

$ ./sayHello.sh "my name is Inigo Montoya"
Hello my name is Inigo Montoya

Deploy the Artifacts

mvn deploy

Main Points

1. This project uses both module inheritence and module aggregation patterns. This allows reuse and single point of project management.
2. The parent pom defines the dependencyManagement so that child modules do not need to redeclair everything.
3. The dependency defined on the multi-module-core artifact is scoped as runtime. The goal here is for the application to depend in compile time only on the API, not its implementation (i.e. the classes in the multi-module-core artifact are not available in compile time). This way it is simpler to keep the separation and the abstraction.
4. The parent pom defines the distributionManagement for both releases and snapshots repositories. In the example, the target repositories are actually in the user's home directory in the local file system.
5. Importing the dependency management from a different pom module (in this example, spring framework) ensures using the right versions for relevant dependencies.
6. Bonus- Running the application from the command line using the exec plugin - see the sayHello.sh bash script.