Converting a java-List<T> into a stream usable with iomicrometer's MultiGauge

Question

from my springboot app i receive a list of results List<T> with 100 Elements read from a database table using

T contains the fields

• unique identifier
• longitude
• latitude
• value

i want to turn this into multiple micrometer-gauges like

object{id=<unique identifier>,longitude=<longitude>,latitude=<latitude>} <value>
object{id=<unique identifier>,longitude=<longitude>,latitude=<latitude>} <value>
object{id=<unique identifier>,longitude=<longitude>,latitude=<latitude>} <value>
...

The metrics shall be scraped by prometheus and then visualized using grafana/worldmap i am building my multi-gauge using MultiGauge l100 = MultiGauge.builder("metric-last100").register(registry);

and terribly failing at converting that List<T> into a stream to feed l100.register(...) as shown here:

// SELECT count(*) from job group by status WHERE job = 'dirty'     
MultiGauge statuses = MultiGauge.builder("statuses")
        .tag("job", "dirty")
        .description("The number of widgets in various statuses")
        .baseUnit("widgets")
        .register(registry);

...

// run this periodically whenever you re-run your query     
statuses.register(
  resultSet.stream().map(result -> 
    Row.of(Tags.of("status", result.getAsString("status")),     
    result.getAsInt("count")))
)

Here is my actual code:

private MultiGauge l100;
...
l100 = MultiGauge.builder("ids-metric-last100").register(registry);
...   
public void updateMetricLast100Deliveries() {
  List<C3MpGeodataDOM> last100 = c3MpGeodataDAO.getlast100();

  l100.register(
    last100.stream().map(
        res -> Row.of(
            Tags.of(
                "sdgnr", res.getMpPK().getSdgnr(),
                "latitude", "" + res.getGeo_latitude(),
                "longitude", "" + res.getGeo_longitude()),
            1)));
}

Please forgive me my dumbness, can someone please help?

thanks

/M

Answer 1

You can try to do something like this:

1 - Create a class to store your results and convert the data to a MultiGauge.Row

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class UserData {

  private String gender;
  private Long counter;

  public MultiGauge.Row<UserData> toRow() {
    return MultiGauge.Row.of(Tags.of("gender", gender), this, c -> this.counter);
  }

}

2 - Create a custom query to group your results

@Query(value = "select new multigauge.multigauge.UserData(usr.gender, count(usr.id)) " +
    "from users usr " +
    "group by usr.gender")
   List<UserData> retrieveUsersGroupedByGender();

3 - Convert the list using the toRow method and register your MultiGauge

@Scheduled(fixedDelay = 1000)
  public void updateGauges() {
    multiGauge.register(userRepository.retrieveUsersGroupedByGender()
      .stream()
      .map(UserData::toRow)
      .collect(toList()), true);
  }

4 - Initialize your MultiGauge

@PostConstruct
  public void init() {
    multiGauge = MultiGauge.builder("users_grouped_by_gender_metric").register(prometheusMeterRegistry);
  }

I recommend taking a look at the unit tests from the official GitHub repo:

https://github.com/micrometer-metrics/micrometer/blob/master/micrometer-core/src/test/java/io/micrometer/core/instrument/MultiGaugeTest.java