Oh yes, these two modules "pmd-java8" and "pmd-ui" are for java8 only and pmd is released with java7 - hence the the parent pom version has not been adjusted during the release.
You can disable the modules for now by executing this maven command:
mvn -P\!jdk8-modules clean package //使用这个命令就能正常编译
This disables the profile "jdk8-modules" so that the two modules are not built.
解决方法来自：https://sourceforge.net/p/pmd/discussion/188193/thread/5f30e7cf/
maven编译pmd出现异常（Non-resolvable parent POM for net.sourceforge.pmd:pmd-java8）【记录】
原文：http://www.cnblogs.com/successjerry/p/5207836.html