def from_file(file)
      check_read_only

      if file && File.exist?(file)
        file = File.expand_path(file)
        RubyUtils.loadPropertiesFile(spark_conf, file)
      end
    end
def from_file(file)
      check_read_only

      if file && File.exist?(file)
        file = File.expand_path(file)
        RubyUtils.loadPropertiesFile(spark_conf, file)
      end
    end
Initialize java SparkConf and load default configuration.