Address review comments

flink-connector-bigquery-examples/src/main/java/org/apache/flink/examples/gcp/bigquery/BigQueryExample.java

@@ -32,19 +32,27 @@
 import org.slf4j.LoggerFactory;
 
 /**
- * A simple BigQuery table read example with Flink's DataStream API.
+ * A simple Flink application using DataStream API and BigQuery connector.
  *
- * <p>The Flink pipeline will try to read the specified BigQuery table, potentially limiting the
- * element count to the specified row restriction and limit count, returning {@link GenericRecord}
- * representing the rows, to finally prints out some aggregated values given the provided payload's
- * field.
+ * <p>The Flink pipeline will try to read the specified BigQuery table, limiting the element count
+ * to the specified row restriction and limit, returning {@link GenericRecord} representing the
+ * rows, and finally print out some aggregated values given the provided payload's field. The
+ * sequence of operations in this pipeline is: <i>source > flatMap > keyBy > max > print</i>.
  *
- * <p>Note on row restriction: In case of including a restriction with a temporal reference,
- * something like {@code "TIMESTAMP_TRUNC(ingestion_timestamp, HOUR) = '2023-06-20 19:00:00'"}, and
- * launching the job from Flink's Rest API is known the single quotes are not supported and will
- * make the pipeline fail. As a workaround for that case using \u0027 as a replacement will make it
- * work, example {@code "TIMESTAMP_TRUNC(ingestion_timestamp, HOUR) = \u00272023-06-20
- * 19:00:00\u0027"}.
+ * <p>Flink command line format to execute this application: <br>
+ * flink run {additional runtime params} {path to this jar}/BigQueryExample.jar <br>
+ * --gcp-project {required; project ID which contains the BigQuery table} <br>
+ * --bq-dataset {required; name of BigQuery dataset containing the desired table} <br>
+ * --bq-table {required; name of BigQuery table to read} <br>
+ * --agg-prop {required; record property to aggregate in Flink job} <br>
+ * --restriction {optional; SQL-like filter applied at the BigQuery table before reading} <br>
+ * --limit {optional; maximum records to read from BigQuery table}
+ *
+ * <p>Note on row restriction: In case a restriction relies on temporal reference, something like
+ * {@code "TIMESTAMP_TRUNC(ingestion_timestamp, HOUR) = '2023-06-20 19:00:00'"}, and if launching
+ * the job from Flink's Rest API, a known issue is that single quotes are not supported and will
+ * cause the pipeline to fail. As a workaround, using \u0027 instead of the quotes will work. For
+ * example {@code "TIMESTAMP_TRUNC(ingestion_timestamp, HOUR) = \u00272023-06-20 19:00:00\u0027"}.
  */
 public class BigQueryExample {
 
@@ -59,8 +67,8 @@ public static void main(String[] args) throws Exception {
                     "Missing parameters!\n"
                             + "Usage: flink run <additional runtime params> BigQuery.jar"
                             + " --gcp-project <gcp-project> --bq-dataset <dataset name>"
-                            + " --bq-table <table name> --agg-prop <payload's property>"
-                            + " --restriction <single-quoted string with row predicate>"
+                            + " --bq-table <table name> --agg-prop <record property>"
+                            + " --restriction <optional: row filter predicate>"
                             + " --limit <optional: limit records returned>");
             return;
         }
@@ -114,7 +122,7 @@ private static void runFlinkJob(
 
         env.fromSource(bqSource, WatermarkStrategy.noWatermarks(), "BigQuerySource")
                 .flatMap(new FlatMapper(recordPropertyToAggregate))
-                .keyBy(t -> t.f0)
+                .keyBy(mappedTuple -> mappedTuple.f0)
                 .max("f1")
                 .print();