// read the BigQuery data
PCollection<TableRow> bigQuerySource = p
    .apply(BigQueryIO.readTableRows().fromQuery(bigQueryQuery).usingStandardSql().withTemplateCompatibility());

..
public void processElement(ProcessContext c) {
  Set<Map.Entry<String, Object>> entries = c.element().entrySet();
  for (Map.Entry<String, Object> entry : entries) {
    Object value = entry.getValue();
    String x = value.getClass().getName();
  }
..