pom.xml

<plugin>
  <groupId>org.xolstice.maven.plugins</groupId>
  <artifactId>protobuf-maven-plugin</artifactId>
  <version>${protobuf-maven-plugin.version}</version>
  <configuration>
    <protocArtifact>
      com.google.protobuf:protoc:3.3.0:exe:${os.detected.classifier}
    </protocArtifact>
    <pluginId>grpc-java</pluginId>
    <pluginArtifact>
      io.grpc:protoc-gen-grpc-java:1.4.0:exe:${os.detected.classifier}
    </pluginArtifact>
    <outputDirectory>
      generated-sources/
    </outputDirectory>
    <clearOutputDirectory>false</clearOutputDirectory>
  </configuration>
  <executions>
    <execution>
      <goals>
        <goal>compile</goal>
        <goal>compile-custom</goal>
      </goals>
    </execution>
  </executions>
</plugin>