I faced same problem today. And I found out a solution for this problem. It’s pretty simple.
Just add jcl-over-slf4j
dependency to forward JCL logging (Apache Commons Logging) to slf4j.
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>jcl-over-slf4j</artifactId>
<version>1.7.5</version>
</dependency>
After that you can config log file as Log4j Examples.
If you use logback
you can put the following to your logback.xml
<logger name="org.apache.http" level="DEBUG"/>
Or if you use log4j
log4j.logger.org.apache.http=DEBUG