code: static ImmutableList<GroupResult> groupActiveFindingsWithSourceAtTime(SourceName sourceName) {
      try (SecurityCenterClient client = SecurityCenterClient.create()) {
        // SourceName sourceName = SourceName.of(/*organization=*/"123234324",/*source=*/
        // "423432321");
  
        // 1 day ago
        Instant oneDayAgo = Instant.now().minusSeconds(60 * 60 * 24);
  
        GroupFindingsRequest.Builder request =
            GroupFindingsRequest.newBuilder()
                .setParent(sourceName.toString())
                .setGroupBy("category")
                .setFilter("state=\"ACTIVE\"")
                .setReadTime(
                    Timestamp.newBuilder()
                        .setSeconds(oneDayAgo.getEpochSecond())
                        .setNanos(oneDayAgo.getNano()));
  
        // Call the API.
        GroupFindingsPagedResponse response = client.groupFindings(request.build());
  
        // This creates one list for all findings.  If your organization has a large number of
        // findings
        // this can cause out of memory issues.  You can process them batches by returning
        // the Iterable returned response.iterateAll() directly.
        ImmutableList<GroupResult> results = ImmutableList.copyOf(response.iterateAll());
        System.out.println("Findings:");
        System.out.println(results);
        return results;
      } catch (IOException e) {
        throw new RuntimeException("Couldn't create client.", e);
      }
    }
docs: [START group_active_findings_with_source_at_time]