I am reading an interesting tutorial here: http://www.avajava.com/tutorials/lessons/how-do-i-generate-pmd-and-cpd-reports-for-a-site.html?page=1
This tutorial shows
The maven-pmd-plugin by default skips nowadays empty reports (property skipEmptyReport). You'll need to set this to false, to get in your site always a PMD/CPD report:
org.apache.maven.plugins
maven-pmd-plugin
3.4
false
This applies for both PMD and CPD. I assume, this is your problem, as in Figure 2, you show, there are no PMD violations detected (pmd.xml file is empty).
The property minimumTokens configures CPD and defines how long a code snipped at a minimum must be to be declared as a duplicate. The lower the number, the more duplicates are detected, but the duplicates can also be much shorter and therefore maybe more often false positives.
Without further configuring maven-pmd-plugin it uses by default these three PMD rulesets: java-basic, java-imports, java-unusedcode. See also property rulesets. If you want to detect specific problems, then you'll need to enable these rules. See also How to make a ruleset.