Smack slf4j debugger. Inspect the exchanged XMPP stanzas. Connect your favourite slf4j backend of choice to get output inside of it
'org.igniterealtime.smack:smack-debug-slf4j:4.1.3'
<dependency>
<groupId>org.igniterealtime.smack</groupId>
<artifactId>smack-debug-slf4j</artifactId>
<version>4.1.3</version>
</dependency>
<dependency org="org.igniterealtime.smack" name="smack-debug-slf4j" rev="4.1.3"/>
"org.igniterealtime.smack", "smack-debug-slf4j", "4.1.3"