B4A Library jMQTT - Official Android MQTT client

The B4J jMQTT library is fully compatible with B4A: https://www.b4x.com/android/forum/threads/59472/#content

A tutorial about MQTT: [IoT] MQTT Protocol

Implementation of the same example is attached (you need to set the user name and password if you like to test it).

 

[sixteen]

Hi,Erel,Where can I download the lib? thanks a lots!

I had found it!,thanks for your works~!

 

[Erel]

In case it is not clear, the jMQTT is a B4A and B4J library.

 

[coslad]

So, mqtt can replace push framework!!! Good!

 

[Erel]

That is not really correct. The main advantage of GCM (Google push service) is that it will work even if the process is not running. This is not the case with any other solution that requires an active network connection.

 

[b4auser1]

The canvas client works perfectly with the MQTT Broker on tcp port.
I tried to use SSL port in URI for mqtt.Initialize and got the error:
"(SocketException) java.net.SocketException: Connection reset".

How to setup mqtt client to use SSL ?

 

[Erel]

The ServerURI should start with ssl:// instead of tcp://

 

[b4auser1]

Erel,

Thank you very much !
With "ssl://" it works.

 

[sarmanho]

Erel,
Which brokers MQTT do you recommend for thousands of simultaneous connections?
What is the best brokers MQTT?

 

[Erel]

Mosquitto is a very popular broker. I haven't run any server side performance tests.

 

[Mr Mo]

Hi all,
I am just a one week newbie. My first try is working with jMQTT.
My application dialog with an Arduino broker via Wifi. The Arduino is connected by Nrf24L01 to 3 sensors.
I have no problem with subcribed message.
If I try to publish... it seem not working.
The topic is MyMQTT/21/1/V_LIGHT and the payload must be "0" or "1".
For information I have other application working with this Arduino broker.
Here is the code for publishing.
Any help welcome.

Sub tbnLight_CheckedChange(Checked As Boolean)
    Dim msg(1) As Byte
    Select tbnLight.Checked
        Case True
            msg(0) = 0x31
        Case False
            msg(0) = 0x30
    End Select
    Log("Sent Payload: " & BytesToString(msg, 0, msg.Length, "utf8"))
    Try
        mqtt.Publish("MyMQTT/21/1/V_LIGHT",msg)
    Catch
        Log(LastException)
        If mqtt.Connected = False Then
            mqtt.Connect
        End If
    End Try
End Sub

 

[Erel]

Please start a new thread for this (in the questions forum).

 

[TommyBee]

I tried to use SSL port in URI for mqtt.Initialize and got the error:
(CertificateExpiredException) java.security.cert.CertificateExpiredException

I use my own Cloudmqtt, the unsecure connection works fine, what's to do to fix that?
Thanx in advance.

 

[Erel]

Note that the URI should start with ssl:// instead of tcp://. However currently self signed certificates are not supported by this library.

 

[TommyBee]

Yes indeed, it starts with ssl://
I use no self signed certificates, i just try to connect to ssl://m20.cloudmqtt.com:27019 then i get this error.
With tcp://m20.cloudmqtt.com:17019 it works.

 

[TommyBee]

Hi Erel,
could you please add this Paho-Callback to the library:

deliveryComplete
void deliveryComplete(IMqttDeliveryToken token)
Called when delivery for a message has been completed, and all acknowledgments have been received. For QoS 0 messages it is called once the message has been handed to the network for delivery. For QoS 1 it is called when PUBACK is received and for QoS 2 when PUBCOMP is received. The token will be the same token as that returned when the message was published.

Think it's essentielly needed in most all cases.
Thank's in advance

 

[Erel]

Why do you need it? If you need to make sure that the message is delivered then set the QOS to 1 or 2. If it will not be delivered then the connection will break.

 

[oymyakon]

Hi,
When i receive a payload i get [B@996b933 instead of the string i sent (20.6 C, 6.0, -57) can you help paul.

 

[Erel]

Payload is an array of bytes. It is not a string.

You can convert it to a string with:

Log(BytesToString(Payload, 0, Payload.Length, "utf8"))

 

[haungmaojung]

Hi Erel,
1. I found that jMQTT library did not support client to set up LWT (Last Will Testment)
2. I've setup a client (MQTT-Spy running on my NB computer) to publish message with
a last will message> Will-Topic: 'LastWill/Sensor1' Will-Payload: 'sensor lost contact'
3. Then I created a situation(unplug RJ45 cable) to simulate network error to
cause Broker to publish Last will message
4. In my B4A android device, I've subscribe this topic(modify MQTTCanvas sample)
5. When KeepAlive interval timeout, MQTTCanvas received a message callback,
but it prompts Error Occurred
---------------------------------------------------------------------
An error has occurred in sub:main_mqtt_messagearrived(java
line: 487)
java io.IOException
Continue?

I found the error line 487 in b4a java source code which is
......
//BA.debugLineNum = 83;BA.debugLine="obj = serializator.ConvertBytesToObject(Payload)";
_obj = _serializator.ConvertBytesToObject(_payload);
....

Did I miss something? Please help.

Best Regards,
Victor