code: public static String getWriteDisposition(Configuration conf) {
      return conf.get(
          BigQueryConfiguration.OUTPUT_TABLE_WRITE_DISPOSITION_KEY,
          BigQueryConfiguration.OUTPUT_TABLE_WRITE_DISPOSITION_DEFAULT);
    }
docs: Gets the write disposition of the output table. This specifies the action that occurs if the
  destination table already exists. By default, if the table already exists, BigQuery appends
  data to the output table.
  
  @param conf the configuration to reference the keys from.
  @return the write disposition of the output table.