Java gateway item key validation currently accepts strictly 2 item key parameters.
Zabbix 3.4 added JMX discovery, which is a great feature - but currently it is not possible to use this feature to discover multiple JVMs on a host.
Consider a solution that knows about the JMX ports and can send a JSON to a Zabbix LLD rule. While a different port can be used in the JMX endpoint field, it all breaks in the item prototypes - an item cannot be created for multiple JVMs as the item key would be the same.
There is a very simple solution - accept 2 or 3 item key parameters. With a one-line change, Zabbix JMX functionality becomes much more powerful.
While we have it hacked in our gateway already and it is working great, it would be a useful feature for other users, and having it upstream would remove the need for us to patch that one line.