Boost Your IoT Apps with mica-mqtt: A Low‑Latency Java AIO MQTT Engine

Introduction

mica-mqtt is an open‑source MQTT component built on Java AIO that delivers a simple, low‑latency, high‑performance solution for IoT messaging. It is easy to integrate into existing services and reduces the cost of developing custom IoT platforms.

Features

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

Supports the WebSocket MQTT sub‑protocol (compatible with mqtt.js).

Provides an HTTP REST API (documentation referenced separately).

Includes MQTT client libraries.

Includes MQTT server implementation.

Supports MQTT will messages.

Supports retained MQTT messages.

Enables custom message (mq) processing and forwarding for clustering.

Provides an Alibaba Cloud MQTT connection demo for clients.

Supports GraalVM compilation to native executables.

Offers a Spring Boot starter for rapid integration ( mica-mqtt-spring-boot-starter).

The starter integrates with Prometheus and Grafana for monitoring.

Cluster support via Redis pub/sub (see mica-mqtt-broker module).

Use Cases

IoT cloud‑side MQTT broker.

Edge‑side IoT message communication.

Group‑based instant messaging.

Message push services.

Simple, easy‑to‑use MQTT client applications.

Changelog

2.2.5 - 2023‑10‑05

✨ MQTT business thread pool now supports custom settings using Java 21 virtual threads.

✨ Updated GitHub Actions to use Java 21 instead of Java 17.

✨ Deprecated ThreadUtil (temporarily retained) and switched to ThreadUtils from mica‑net.

Custom Business Thread Pool

5.1 Adjusting Business Threads for mica-mqtt Client

Important: The default business thread count for the client is 2 , which is sufficient for most lightweight scenarios.

If your client processes a large volume of messages, has long‑running business logic, or exhibits latency or memory growth, you can increase the thread pool size.

Standard Java configuration:

// Initialize MQTT client
MqttClient client = MqttClient.create()
    .ip("127.0.0.1")
    .port(1883)
    .username("admin")
    .password("******")
    // Set business thread pool; typically cpuCores * 2
    .mqttExecutor(ThreadUtils.getBizExecutor(10))
    .connect();

Spring Boot starter configuration:

@Configuration(proxyBeanMethods = false)
public class MqttClientCustomizerConfiguration {

    @Bean
    public MqttClientCustomizer mqttClientCustomizer() {
        return creator -> {
            // Set business thread pool; typically cpuCores * 2
            creator.mqttExecutor(ThreadUtils.getBizExecutor(10));
        };
    }
}

If you are on Java 21 and need to handle massive message volumes, you can use virtual threads:

@Configuration(proxyBeanMethods = false)
public class MqttClientCustomizerConfiguration {

    @Bean
    public MqttClientCustomizer mqttClientCustomizer() {
        return creator -> {
            // Use Java 21 virtual threads for business execution
            creator.mqttExecutor(Executors.newVirtualThreadPerTaskExecutor());
        };
    }
}

5.2 Configuring mica-mqtt Server

The server’s default business thread count is twice the number of CPU cores (minimum 8). For heavy workloads, consider offloading processing to Kafka or RocketMQ and scaling consumer services.

Documentation & Resources

MQTT fundamentals, mqttx, and mica-mqtt tutorial videos: https://b23.tv/VJ8yc7v

mica-mqtt quick‑start repository: https://gitee.com/596392912/mica-mqtt