Drupal not connecting to Solr Server
There can be two things which I can think of.


Most SOLR installation guides advise you to edit IPAccessHandler in server/etc/jetty.xml to whitelist certain IP addresses. Often this is 127.0.0.1, but that would prevent access from localhost via IPv6. So you maybe should also white label the IPv6 localhost address ::1, or connect explicitly via IPv4 127.0.0.1.
Since SOLR 4.x you should also include your core name in the url. Search API Solr clearly states this. It might apply to Apache Solr module as well. This would mean your should enter a URL like: http://localhost:8983/solr/&lt;core name&gt;.