When a single codebase contains multiple standalone applications, each with its own entry point, the build process must generate separate executable artifacts. Consider a project containing both a command-line utility and a network service.

Define the entry points in separate packages to maintain clear bonudaries:

package com.myapp.cli;

public class DataImporter {
    public static void main(String[] arguments) {
        System.out.println("Initializing data import sequence");
    }
}

package com.myapp.api;

public class RestGateway {
    public static void main(String[] arguments) {
        System.out.println("Starting HTTP gateway on port 8080");
    }
}

Configure the maven-shade-plugin to create multiple shaded JARs during the package phase. Each execution generates an independent artifact with its own manifest pointing to the correct main class:

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-shade-plugin</artifactId>
      <version>3.5.1</version>
      <executions>
        <execution>
          <id>package-importer</id>
          <phase>package</phase>
          <goals>
            <goal>shade</goal>
          </goals>
          <configuration>
            <shadedArtifactAttached>true</shadedArtifactAttached>
            <shadedClassifierName>importer</shadedClassifierName>
            <transformers>
              <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                <mainClass>com.myapp.cli.DataImporter</mainClass>
              </transformer>
            </transformers>
          </configuration>
        </execution>
        <execution>
          <id>package-gateway</id>
          <phase>package</phase>
          <goals>
            <goal>shade</goal>
          </goals>
          <configuration>
            <shadedArtifactAttached>true</shadedArtifactAttached>
            <shadedClassifierName>gateway</shadedClassifierName>
            <transformers>
              <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                <mainClass>com.myapp.api.RestGateway</mainClass>
              </transformer>
            </transformers>
          </configuration>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

Execute the build to generate all artifacts:

mvn clean package

This porduces three JAR files in target/: the original unshaded JAR, plus two executable varients with classifiers importer and gateway. Run either application using:

java -jar target/myapp-1.0.0-importer.jar
java -jar target/myapp-1.0.0-gateway.jar