TCP: Connection refused
UDS: File not found (nonexistent file or device) ((the translation may not be correct, sorry))

TCP: jdbc:mysql://localhost/<dbname>?user=<user>&password=<pwd>&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC&characterEncoding=utf8
UDS: jdbc:mysql:///<dbname>?socketFactory=com.mysql.jdbc.NamedPipeSocketFactory&namedPipePath=/var/run/mysqld/mysqld.sock&user=<user>&password=<pwd>&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC&characterEncoding=utf8

Class.forName("java.sql.Driver");
...
Connection db = DriverManager.getConnection(Settings.sqlConnection.value);
try(Statement stmt = c.createStatement())
{
    stmt.execute("SET @now = UTC_TIMESTAMP()");
}
...

Debian 8.7
MySQL server 5.5.53-0+deb8u1
java version "1.7.0_181"
OpenJDK Runtime Environment (IcedTea 2.6.14) (7u181-2.6.14-1~deb8u1)
OpenJDK 64-Bit Server VM (build 24.181-b01, mixed mode)
mysql-connector-java-5.1.42.jar