Best Practices for managing JavaFX Screens

[feral nimbus]

I tried a few approaches for managing "screens" from fxml centrally, but none was satisfactory to me.
I tried implementing a dynamic registry, but searching through the classpath was too complicated for me.
I tried having a public static method to load the scene, but that meant a lot of duplicated code for loading fxml and needlessly implemented methods that all do the same.
My internal code quality metrics tell me that thats not a good solution either.

So are there any libraries that i could look at or well known patterns that i could follow?

[proper lake]

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[peak dragon]

Hello, I've been trying to solve this issue for 5 years now and after that time I have come up with a custom made framework. I can post here a link but it is still in development and not sure when I will release some stable version. Most of the API I have should be stable, but from time to time I'm forced to introduce a breaking change...

[feral nimbus]

I would be thankful if you would share a high level overview how it works.

[proper lake]

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[peak dragon]

I have a documentation for it, but it is also in progress...

https://jfxsoft.gitlab.io/docs/getting_started/

[celest hearth]

Can you elaborate on why you "need" to manage screens as opposed to creating one method capable of loading any given "screen" and calling that whenever you need that?

[peak dragon]

From my personal experience it is simply not enough to have one simple static method for loading screens. Maybe for very simple applications with very few screens it would be enough. But for something more complex I think it makes sense to have a more robust solution...

[celest hearth]

What exactly is not sufficient for you

I am sometimes using an abstract base class for controllers with custom init methods etc and then I more or less have static methods for loading

(or in principle code generation is possible as well)

but it depends on your exact requirements

[peak dragon]

Years ago (Java 8 was new)I found a very nice tutorial on YouTube for very simple managing screens. It was able to switch one screen into another one. It was also supporting animations between transitions from one screen to another.

But then I started building much more complex applications where I had screens built from other screens (single blocks) and then I realised it is not enough for me.

[celest hearth]

oh that's what you want to do

yeah for that you need some sort of classpath scanning or code generation

[peak dragon]

Form with a single button is not enough for business applications...

[celest hearth]

but you can do some very simple classpath scanning for that

I assume you are using FXML for all your screens?

[peak dragon]

Yep

[celest hearth]

Is it possible to create one folder (in your resources) where all of these FXML files are contained in and follow a naming convention such that no non-screen FXML files in that folder match the naming convention?

[peak dragon]

Then I started thinking about how to separate business logic from the view. So I had to distinguish between the view controller (bound to a view) and the "form" controller which contains logic+ services for real stuff...

[peak dragon]

Yeah, I have a single directory in resources for views. I went a bit further and separated views by logical part of the application

Then I have prepared a lot of "standard" predefined views with some minimal logic. So for example a login dialog with validation would be quite easy to create...

[celest hearth]

You should be able to do something like

String folder = "/your/screens";
try(BufferedReader folderEntryReader = new BufferedReader(getClass().getClassLoader().getResourceAsStream(folder)){
  List<String> fxmlResources = folderEntryReader.lines().filter(line -> line.endsWith(".fxml")).map(folderEntry -> folder+"/"+folderEntry).toList();
  // ...
}

[peak dragon]

And for resources, I got inspired by Android and have a plugin which discovers all resources and generates a class with paths to each resource so loading is also easy...

[celest hearth]

and then you can load the views and the controller with FXMLLoader normally

and if you want to use some sort of dependency injection for the business logic, that's an option as well

[peak dragon]

I could have resources placed in multiple java/maven modules so I have implemented a "discovery" process to allow load view from any module...

[celest hearth]

That's possible as well using things like the service loader API

[peak dragon]

Yeah, that's what I'm using 😁

[celest hearth]

you can implement something where classes can register themselves and these classes then know where you can find the FXML files

i.e. the classes know about the directories

[celest hearth]

or just that if all modules use the same class loader

[feral nimbus]

I need to build a framework that facilitates quickly building Applications for internal use. Our requirements are pretty specific so existing frameworks would not help too much. (Certification processes are bitches)

I'll likely use Spring boot and services for it. Even if it seems overkill. But we need to evaluate spring for our backends anyways

[celest hearth]

What I said before still applies

Also do you need to certify every single small library you are adding?

[feral nimbus]

I likely will have to.

[celest hearth]

You can do simple classpath scanning without external libraries as I've shown before

[feral nimbus]

I've tried this before, but it did not work too good.

[celest hearth]

What was the issue?

[feral nimbus]

I had the problem that my library was inside it's own package and I had a registration step where I would pass a class to my library to search the entire package of that class, but only views contained in the same package like the library were found.

[celest hearth]

I think you called getClass() on a library object or used .class

if you use .getClass().getClassLoader(), it should search from the classpath root

[feral nimbus]

That's what I did

[celest hearth]

and the same should apply when the path starts with a /

[celest hearth]

and that's why it happened

by default, it uses the package of the class

you can use getClassLoader() or start it with a /

[feral nimbus]

Another weirdly mysterious Java detail 😅

[celest hearth]

it isn't that mysterious

it's literally in the docs

[feral nimbus]

I tried with getClassLoader() too, but it did not work as I expected. It showed me files that it wasn't supposed to find and did not find ones I wanted it to find. But maybe my code was shit.

[celest hearth]

Note: Class#getResourceAsStream doesn't work across modules I think

and even for ClassLoader#getResourceAsStream, the package should be exported

[celest hearth]

Are the packages exported to the library module?

[feral nimbus]

Yes. But I would not trust my code in that case.

[celest hearth]

actually nvm it needs to be opened unconditionally

not exports to but opens

[feral nimbus]

Maybe that was the weird part.

I exported them

I'll go and try to whip something up so I can test. But I'd like to not close the thread for now.

[celest hearth]

otherwise if you have access to a Class, you can use the getResourceAsStream method on that Class with a leading / to accesses resources of that module

[celest hearth]

that should also work without opening/exporting I think

[celest hearth]

Resources in named modules are subject to the encapsulation rules specified by Module.getResourceAsStream. Additionally, and except for the special case where the resource has a name ending with ".class", this method will only find resources in packages of named modules when the package is opened unconditionally (even if the caller of this method is in the same module as the resource).

https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/ClassLoader.html#getResource(java.lang.String)

actually the "opens" is also a requirement with Class#getResourceAsStream

Resources in named modules are subject to the rules for encapsulation specified in the Module getResourceAsStream method and so this method returns null when the resource is a non-".class" resource in a package that is not open to the caller's module.

https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/Class.html#getResourceAsStream(java.lang.String)

but for that, opens to is sufficient