B4J Question MQTT connecting into SSL:// throws an error


Licensed User
Hi There! I got a question regarding MQTT connecting thru SSL into my mosquitto broker.

The SSL certificate I got installed on my server is from https://letsencrypt.org/ ...

I already got a B4A app running with MQTT using this connection. In B4A I got no error...

But on B4J, I get the following error: (SunCertPathBuilderException) sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target

What can I do to remediate this ?



B4X founder
Staff member
Licensed User
Try to update Java. The newer version might include the required certificates.

It is also possible to trust all certificates.

Try this:
    Dim mo As MqttConnectOptions
   mo.Initialize("aa", "bb")
   Dim jo As JavaObject = mo
   jo.RunMethod("setSocketFactory", Array(CreateTrustAllSSLSocketFactory))
 'Use Mqtt.Connect2(mo)

Sub CreateTrustAllSSLSocketFactory As Object
   Dim tm As CustomTrustManager
   Dim SSLContext As JavaObject
   SSLContext = SSLContext.InitializeStatic("javax.net.ssl.SSLContext").RunMethod("getInstance", Array("TLS"))
   SSLContext.RunMethod("init", Array(Null, tm, Null))
   Dim Factory As JavaObject = SSLContext.RunMethod("getSocketFactory", Null)
   Return Factory
End Sub

Depends on jNet library.
Last edited:
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Licensed User
Thank you Erel,

Yes! Both of your suggestions worked fine. I updated Java SDK into version 8 update 181, and it cleared ok the root certificate from letsencrypt.

Also, before trying to update the Java SDK, i tried your code, and it also worked fine (side note: in Sub CreateTrustAllSSLSocketFactory, the return line at the end says Factrory (extra 'r').

I decided not to use your code, but just trust the java updated certificate thing, which sounds like the most secure / judicious thing to do :)
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