Recommended way to use Distributed Counters (ADR-49) in the Java NATS client

[burl21]

Hi everyone

I’m experimenting with the new Distributed Counters feature (ADR-49) and wanted to confirm whether the following is the recommended or intended usage.

Here’s a minimal example:

// docker run --rm -p 4222:4222 nats:latest -js
void testCounterStream() {
  record RespBody(String stream, long seq, String val) {}

  try (var connection = Nats.connect()) {
    var jsonMapper = JsonMapper.builder().build();
    var jsm = connection.jetStreamManagement();
    jsm.addStream(
        StreamConfiguration.builder()
            .name("test-counter")
            .allowMessageCounter(true)
            .build()
    );

    var headers = new Headers();
    headers.add("Nats-Incr", "+" + 10);

    var natsMsg = NatsMessage.builder()
        .subject("test-counter")
        .headers(headers)
        .build();

    var respMsg = connection.request(natsMsg, Duration.ofMillis(100));
    assertNotNull(respMsg)
    
    var respBody = jsonMapper.readValue(respMsg.getData(), RespBody.class);

    assertEquals("test-counter", respBody.stream);
    assertEquals(1, respBody.seq);
    assertEquals("10", respBody.val);
  } catch (Exception e) {
    fail(e);
  }
}

Thanks in advance

[scottf]

Please look at the Orbit project: https://github.com/synadia-io/orbit.java/tree/main/counters

There is a complete example here: https://github.com/synadia-io/orbit.java/blob/main/counters/src/examples/java/io/synadia/examples/CounterExample.java