Single Instance Application is an optional feature, which ensures that there is only one instance of your application running, even if the user starts the application several times.

This feature is provided out-of-the-box. It is disabled by default, however, but can be enabled by simply specifying the defaultSingleInstancePort property of the Drombler FX Maven Plugin.

        <!--Uncomment the following line and
            specifcy an unused port to create a single instance application -->
        <!--<defaultSingleInstancePort>some unused port</defaultSingleInstancePort>-->

Use a port which is unlikely already be used on your customers computer. This also means that it’s recommended to use a different port for each application.

At first start, the application will check if the port is free. If not, it will try to find another free port. The port used by the application is then configured in the userdir at "conf/" as the "port" property. By changing this property in this configuration file, the user is still able to re-configure the application in case there is another application, which uses the same port but was not running at the time of the first start. The user should stop the application instance before changing this configuration file.

The user is still able to run multiple instances (e.g. for testing purposes), by specifying the "--userdir" command line option as every userdir is treated independently.

If this feature is enabled and one instance is aleady running, each other application start will pass all its unnamed parameters to the first instance and shuts itself then down. Drombler FX will register a new instance of AdditionalArgumentsProvider for every application start notification.

With the Felix SCR annotations (Declarative Services) you can listen for multiple instances with the following class annotation:

@Reference(name = "additionalArgumentsProvider",
           referenceInterface = AdditionalArgumentsProvider.class,
           cardinality = ReferenceCardinality.OPTIONAL_MULTIPLE,
           policy = ReferencePolicy.DYNAMIC)}

Please note that the Data Framework already provides file path arguments support out-of-the-box.