Unlock Low‑Latency IoT Messaging with mica‑mqtt: A Java AIO MQTT Component

1. Introduction

mica-mqtt is a simple, low‑latency, high‑performance MQTT IoT open‑source component built on java aio . It is easy to integrate into existing services and to extend, reducing the cost of developing custom IoT platforms.

2. Features

Supports MQTT v3.1, v3.1.1 and v5.0 protocols.

Supports MQTT over WebSocket (compatible with mqtt.js).

Provides HTTP REST API (documentation in [1]).

Provides MQTT client library.

Provides MQTT server implementation.

Shared subscription for client and server (VIP version uses topic‑tree storage, performance independent of topic count, works with millions of topics).

Supports MQTT will messages.

Supports retained messages.

Custom message processing and forwarding for clustering.

Alibaba Cloud MQTT connection demo.

Supports GraalVM native compilation.

Spring Boot starter for quick integration (

mica-mqtt-spring-boot-starter

).

Prometheus + Grafana metrics via the starter.

Cluster implementation based on Redis pub/sub (see

mica-mqtt-broker

module).

3. Use Cases

IoT cloud MQTT broker.

Edge‑side IoT message communication.

Group chat IM.

Message push services.

Simple, easy‑to‑use MQTT client.

4. Changelog

v2.2.4 – 2023‑09‑02

Merged last year’s shared‑subscription service and improvements.

Optimized topic validation.

When the same clientId subscribes to the same matching topic, the highest QoS is selected.

5. Shared Subscription

mica-mqtt supports two shared‑subscription modes:

Shared subscription using the prefix

$queue/

. Multiple clients subscribe to

$queue/topic

; only one client receives the message.

Group subscription using the prefix

$share/<group>/

. Each group receives the message, but within a group only one client receives it.

Note: If a topic starts with “/”, e.g.,

/topic/test

, the subscription must be

$share/group1//topic/test

.

6. Quick Start

Spring Boot

Client dependency:

<code>&lt;dependency&gt;
  &lt;groupId&gt;net.dreamlu&lt;/groupId&gt;
  &lt;artifactId&gt;mica-mqtt-client-spring-boot-starter&lt;/artifactId&gt;
  &lt;version&gt;${mica-mqtt.version}&lt;/version&gt;
&lt;/dependency&gt;
</code>

Client configuration (application.yml):

<code>mqtt:
  client:
    enabled: true
    ip: 127.0.0.1
    port: 1883
    name: Mica-Mqtt-Client
    clientId: 000001
    user-name: mica
    password: 123456
    timeout: 5
    reconnect: true
    re-interval: 5000
    version: mqtt_3_1_1
    read-buffer-size: 8KB
    max-bytes-in-message: 10MB
    buffer-allocator: heap
    keep-alive-secs: 60
    clean-session: true
    ssl:
      enabled: false
</code>

Subscription example:

<code>@Service
public class MqttClientSubscribeListener {
    private static final Logger logger = LoggerFactory.getLogger(MqttClientSubscribeListener.class);

    @MqttClientSubscribe("/test/#")
    public void subQos0(String topic, byte[] payload) {
        logger.info("topic:{} payload:{}", topic, new String(payload, StandardCharsets.UTF_8));
    }

    @MqttClientSubscribe(value = "/qos1/#", qos = MqttQoS.AT_LEAST_ONCE)
    public void subQos1(String topic, byte[] payload) {
        logger.info("topic:{} payload:{}", topic, new String(payload, StandardCharsets.UTF_8));
    }

    @MqttClientSubscribe("/sys/${productKey}/${deviceName}/thing/sub/register")
    public void thingSubRegister(String topic, byte[] payload) {
        // variable substitution supported since 1.3.8
        logger.info("topic:{} payload:{}", topic, new String(payload, StandardCharsets.UTF_8));
    }
}
</code>

Server dependency:

<code>&lt;dependency&gt;
  &lt;groupId&gt;net.dreamlu&lt;/groupId&gt;
  &lt;artifactId&gt;mica-mqtt-server-spring-boot-starter&lt;/artifactId&gt;
  &lt;version&gt;${mica-mqtt.version}&lt;/version&gt;
&lt;/dependency&gt;
</code>

Server configuration (application.yml):

<code>mqtt:
  server:
    enabled: true
    port: 1883
    name: Mica-Mqtt-Server
    buffer-allocator: HEAP
    heartbeat-timeout: 120000
    read-buffer-size: 8KB
    max-bytes-in-message: 10MB
    auth:
      enable: false
      username: mica
      password: mica
    debug: true
    stat-enable: true
    web-port: 8083
    websocket-enable: true
    http-enable: false
    http-basic-auth:
      enable: false
      username: mica
      password: mica
    ssl:
      enabled: false
</code>

Non‑Spring‑Boot Projects

Client dependency:

<code>&lt;dependency&gt;
  &lt;groupId&gt;net.dreamlu&lt;/groupId&gt;
  &lt;artifactId&gt;mica-mqtt-client&lt;/artifactId&gt;
  &lt;version&gt;${mica-mqtt.version}&lt;/version&gt;
&lt;/dependency&gt;
</code>

Server dependency:

<code>&lt;dependency&gt;
  &lt;groupId&gt;net.dreamlu&lt;/groupId&gt;
  &lt;artifactId&gt;mica-mqtt-server&lt;/artifactId&gt;
  &lt;version&gt;${mica-mqtt.version}&lt;/version&gt;
&lt;/dependency&gt;
</code>

7. Documentation and Examples

MQTT basics, mqttx, and mica-mqtt video tutorials.

mica-mqtt-client documentation.

mica-mqtt-server documentation.

mica-mqtt-client-spring-boot-starter documentation.

mica-mqtt-server-spring-boot-starter documentation.

mica-mqtt HTTP API documentation.

mica-mqtt release notes.