EMQX文档：https://www.emqx.io/docs/zh/v5.0/

1.安装 https://www.emqx.io/zh/downloads

找到自己合适的平台和版本安装
①：后台启动

emqx start

启动成功后可以使用 emqx ping 命令检测节点运行状态，返回 pong 则表示正常运行：

emqx ping

systemctl 启动

sudo systemctl start emqx

sudo systemctl status emqx

ZIP 安装包启动
切换到 EMQX 解压目录，执行以下命令启动 EMQX：

./bin/emqx start

开发模式下可以使用 console 命令在控制台启动 EMQX，该模式可以实时查看 EMQX 启动和运行输出日志信息：

./bin/emqx console

默认监听： http://localhost:18083/
默认登录账号密码：admin public
default_username = “admin”
default_password = “public”
代码如下

 ## emqx配置
emqx:
  api:
    url: http://ip:端口/api/v4/clients/
    username: 用户名称
    password: 用户密码

	@Value("${emqx.api.url}")
	private String url;

	@Value("${emqx.api.username}")
	private String username;

	@Value("${emqx.api.password}")
	private String password;

	/**
	 *  查询网关在线离线状态
	 * @param clientId 客户端标识符
	 * @return 返回在线离线状态
	 */
	@Override
	public String loadEmqxOnlineStatus(String clientId) {

		try {
			String urlStr = url + clientId;
			URL url = new URL(urlStr);
			HttpURLConnection conn = (HttpURLConnection) url.openConnection();
			conn.setRequestMethod("GET");
			conn.setDoInput(true);
			conn.setDoOutput(true);

			String authString = username + ":" + password;
			byte[] authEncBytes = Base64.encodeBase64(authString.getBytes());
			String authStringEnc = new String(authEncBytes);
			// 设置Authorization字段
			conn.setRequestProperty("Authorization", "Basic " + authStringEnc);

			conn.connect();

			int status = conn.getResponseCode();

			if (status == HttpStatus.OK.value()) {
				BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
				String str = "";
				StringBuffer sb = new StringBuffer();
				while ((str = reader.readLine()) != null) {
					sb.append(str);
				}
				// 取出里面的在线离线字段
				String string = sb.toString();
				JSONObject jsonObject = JSONObject.parseObject(string);
				String data = jsonObject.getString("data");
				JSONArray jsonArray = JSONArray.parseArray(data);
				if (jsonArray.size() == 0) {
					return null;
				}
				return jsonArray.getJSONObject(0).getString("connected");
			}
		} catch (IOException e) {
			throw DataHandleException.of(Result.failure(ResultCode.UNAUTHORIZED, "客户端未通过服务端认证,您使用了无效的身份验证凭据"));
		}
		return null;
	}