List<String> getExtraClasspath() {
    String property = getProperty(PropertyNames.CONTAINER_EXTRA_CLASSPATH);
    if (property != null) {
      return ConfigurationPropertyValidator.parseListProperty(property);
    }
    return container.extraClasspath;
  }
Gets the extra classpath elements.

@return the extra classpath elements
jib-maven-plugin/src/main/java/com/google/cloud/tools/jib/maven/JibPluginConfiguration.java