Add an option to intercept executed Commands

[bartoszpop]

Currently, it is not possible to override default option/parameter values transparently for a user.
We use jBang and Camel jBang to run Camel routes. Internally, both these tools use Picocli to provide CLI experience.
It would be very useful to be able to intercept the executed command and override the default values if not explicitly provided as command line arguments. I could use picocli.CommandLine.IDefaultValueProvider but the problem is that I don't have control over 3rd projects which use Picocli, hence I can't customize the picocli.CommandLine instance. The proposed solution is to use Java System Property or Java SPI (java.util.ServiceLoader) to set a listener class.

[remkop]

Two ideas come to mind:

• contact the JBang maintainers and request that they set the picocli built-in PropertiesDefaultProvider as the default provider on the top-level command. That will allow you to configure default values.
• create your own application class with a main method that creates the picocli.CommandLine instance with the JBang @Command-annotated class, and configure that commandline instance with your desired default provider (which may be the picocli built-in PropertiesDefaultProvider). Then, instead of running JBang and Camel JBang, you run your custom application class.

Thoughts?

[bartoszpop]

Hi @remkop, thank you for your feedback.

contact the JBang maintainers and request that they set the picocli built-in PropertiesDefaultProvider as the default provider on the top-level command. That will allow you to configure default values.

I raised a separate pr (camel#16907) to customize parameters with Java System Properties using the ${sys:} syntax which is already supported by Picocli but it was rejected.

create your own application class with a main method that creates the picocli.CommandLine instance with the JBang @Command-annotated class, and configure that commandline instance with your desired default provider (which may be the picocli built-in PropertiesDefaultProvider). Then, instead of running JBang and Camel JBang, you run your custom application class.

Unfortunately, that would be cumbersome to maintain because Camel JBang provides tens of different commands and we would need to keep it in sync. Also, we use JBang with other 3rd-party scripts.

In my opinion, a more general approach within Picocli would be advantageous, offering greater flexibility and more options for customization. PFA a pr (#2364) with the proposed solution

[bartoszpop]

@remkop when is the next Picocli release planned?