In packaged version of Zabbix-Java-Gateway for CentOS7 the startup script in /usr/sbin/zabbix_java_gateway override JAVA_OPTIONS at line 25

JAVA_OPTIONS="-server $JAVA_OPTIONS"
JAVA_OPTIONS="-Dlogback.configurationFile=/etc/zabbix/zabbix_java_gateway_logback.xml"

so is impossibile to use java_gateway with SSL putting a JAVA_OPTIONS line in the config file

the solution is to modify the lines this way:

JAVA_OPTIONS="-server $JAVA_OPTIONS"
JAVA_OPTIONS="$JAVA_OPTIONS -Dlogback.configurationFile=/etc/zabbix/zabbix_java_gateway_logback.xml"

Note that I've found similar problem in java-Gateway 2.4 packaged for CentOS6, in the init script, but the script for CentOS7 and java_gateway 2.4 was fine.