org.apache.solr.client.solrj.impl.HttpSolrClient$RemoteSolrException: Error from server at http://localhost:8983/solr

This issue happens due to below reasons : 

1. This is mostly a case you did not put your core name in url as  http://localhost:8983/solr/<coreName>  ex: http://localhost:8983/solr/product
2.  Host is incorrect
3.  Host is correct but solr is not running at host
4.  port might be disable
5. Firewall issue