@Nullable
  String getUser() {
    String property = getProperty(PropertyNames.CONTAINER_USER);
    if (property != null) {
      return property;
    }
    return container.user;
  }
Gets the username or UID which the process in the container should run as.

@return the configured main class name
jib-maven-plugin/src/main/java/com/google/cloud/tools/jib/maven/JibPluginConfiguration.java