Maven, modules and ports/adapters

Maven describes a build in pom.xml. A module owns a responsibility and can depend on other modules. Ports/adapters protects domain rules from direct dependencies on HTTP, SQL or an interface. PDF Batch Studio has a framework-free core and different adapters. Sharing the core makes sense within this one product. It is not a shared library for all AppFabrik apps.

Example files

01Build a Maven project

Install Maven and check mvn --version with JDK 21. Save pom.xml and src/main/java/tutorial/Main.java in a new folder. package compiles, tests and produces a JAR. The project repositories also include a Maven wrapper.

pom.xml · xmlOpen file

<project xmlns="http://maven.apache.org/POM/4.0.0">
  <modelVersion>4.0.0</modelVersion>
  <groupId>example</groupId><artifactId>learning</artifactId><version>1.0</version>
  <properties><maven.compiler.release>21</maven.compiler.release><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties>
  <dependencies></dependencies>
  <build><plugins>
    <plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-compiler-plugin</artifactId><version>3.14.1</version></plugin>
    <plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-surefire-plugin</artifactId><version>3.5.3</version></plugin>
  </plugins></build>
</project>

Run / check

mvn package dependency:copy-dependencies
java -cp "target/classes:target/dependency/*" tutorial.Main

02Make direction visible

The service knows only Store. MemoryStore implements that port. main wires them together. In the real project, the core does not depend on the Spring controller or JavaFX interface. Those adapters depend on the core.

src/main/java/tutorial/Main.java · javaOpen file

package tutorial;
import java.util.ArrayList;
import java.util.List;
public class Main {
  interface Store { void save(String value); }
  static final class MemoryStore implements Store {
    final List<String> values = new ArrayList<>();
    public void save(String value) { values.add(value); }
  }
  static final class Service {
    final Store store;
    Service(Store store) { this.store = store; }
    void create(String input) {
      if (input == null || input.isBlank()) throw new IllegalArgumentException("Name required");
      store.save(input.trim());
    }
  }
  public static void main(String[] args) {
    var store = new MemoryStore();
    new Service(store).create("  Letters  ");
    System.out.println(store.values);
  }
}

03Check modules selectively

In the PDF repository, ./mvnw -pl core/pdf-batch-core -am test checks the core and required preceding modules. -pl selects modules and -am includes their dependencies. A core test needs no running interface.

04Justify abstractions

The port is useful because desktop, server and tests need different storage. An interface for every trivial helper method would not provide comparable value. Architecture should facilitate a concrete replacement or boundary.

Expected result

The small build produces a stored learning value. The domain rule remains independent of the storage implementation.

Your exercise

Replace MemoryStore with an adapter writing a text file. Which class should handle IOException?

Show the solution and explanation

The file adapter handles the technical IOException and translates it according to the port contract. The service should not depend on java.nio or a file path. Explicitly decide whether the port returns a failure or uses a defined exception.

Project context and sources

The example is simplified for learning. The linked source version shows its use in the project and the checks applied there.

PDF Batch Studio