nats simple test

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This is the first article to start studying NATS, so let’s try simple sending and receiving messages first.

NATS Server

Publish Subscribe model
Publish Subscribe model

Use docker-compose.yml to build a test NATS Server. 

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version: "3.8"

services:
  nats:
    container_name: nats
    image: nats:2.8.4
    ports:
      - 4222:4222

then start

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docker compose up

Java dependency

You need to import NATS Java library in build.gradle 

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implementation 'io.nats:jnats:2.15.3'
// https://search.maven.org/artifact/io.nats/jnats

Java code

You can refer to the SDK nats.java instructions here.

Producer 

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import io.nats.client.Connection;
import io.nats.client.Nats;

private void sendMessage() throws Exception {
  Connection nc = Nats.connect("nats://localhost:4222");
  IntStream.range(0, 10)
      .forEach(i -> nc.publish("subject", ("hello world-" + i).getBytes(StandardCharsets.UTF_8)));
  nc.flush(Duration.ZERO);
  nc.close();
}

Consumer 

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import io.nats.client.Connection;
import io.nats.client.Dispatcher;
import io.nats.client.Nats;

private void receiveMessage() throws Exception {
  Connection nc = Nats.connect("nats://localhost:4222");
  Dispatcher d = nc.createDispatcher((msg) -> {
    String response = new String(msg.getData(), StandardCharsets.UTF_8);
    log.info("Received {}", response);
  });
  d.subscribe("subject");
}

Simple to understand example of sending and receiving.

Reference

NATS Streams and Services: From Zero to Hero