MQTT connection error on 2021b - Unable to resolve the name com.mathwo​rks.mqttcl​ient.clien​t.Client.

I'm facing this error while trying to create an mqtt connection:

>> myMQTT=mqtt('tcp://broker.hivemq.com')
'com.mathworks' package and subpackages will be removed in a future release. There is no simple replacement for this.

Caused by:
    Unable to resolve the name com.mathworks.mqttclient.client.Client.

I just downloaded the mqtt package from file -exchange (mqtt-download).

I'm using matlab 2021b:

-----------------------------------------------------------------------------------------------------
MATLAB Version: 9.11.0.2358333 (R2021b) Update 7
MATLAB License Number:
Operating System: Microsoft Windows 10 Pro Version 10.0 (Build 19045)
Java Version: Java 1.8.0_202-b08 with Oracle Corporation Java HotSpot(TM) 64-Bit Server VM mixed mode
-----------------------------------------------------------------------------------------------------
MATLAB                                                Version 9.11        (R2021b)
Database Toolbox                                      Version 10.2        (R2021b)
Deep Learning Toolbox                                 Version 14.3        (R2021b)
Image Acquisition Toolbox                             Version 6.5         (R2021b)
Image Processing Toolbox                              Version 11.4        (R2021b)
MATLAB Compiler                                       Version 8.3         (R2021b)
MATLAB Compiler SDK                                   Version 6.11        (R2021b)
MATLAB Report Generator                               Version 5.11        (R2021b)
Spreadsheet Link                                      Version 3.4.6       (R2021b)
Statistics and Machine Learning Toolbox               Version 12.2        (R2021b)

Answer 1

[Samay Sagar]

Hi Eduardo,

I have faced a similar issue in the past. To address this issue while trying to create an MQTT connection you need to ensure that the necessary Java Archive (JAR) files are included in the dynamic Java class path. . You can use the “javaaddpath” function to add entries to dynamic Java class path.

javaaddpath(path_to_mqttasync.jar)
javaaddpath(path_to_org.eclipse.paho.client.mqttv3-1.1.0.jar)

To verify that the JAR files were added correctly, run the “javaclasspath” command in MATLAB command window. This will display the current Java class paths, and you should see your JAR files listed under "Dynamic Java Path."

You can now try to establish a MQTT connection.

myMQTT=mqtt('tcp://broker.hivemq.com')

For more information about “javaaddpath” and “javaclasspath” refer the following documentation:

• https://www.mathworks.com/help/releases/R2021b/matlab/ref/javaaddpath.html
• https://www.mathworks.com/help/releases/R2021b/matlab/ref/javaclasspath.html