I was getting the following error when trying to connect to my MySQL database running on localhost using the JDBC MySQL Connector/J:
org.apache.commons.dbcp.SQLNestedException: Cannot create PoolableConnectionFactory (Communications link failure due to underlying exception: ** BEGIN NESTED EXCEPTION ** java.net.ConnectException MESSAGE: Connection refused
The user I was trying to connect with had all the right permissions. The problem was, my hosts file didn't have an IPv4 entry for localhost. Once I added that it worked fine:
# /etc/hosts ::1 localhost.localdomain localhost 127.0.0.1 localhost.localdomain localhost