Encountering a NullPointerException while trying to load a resource from a directory that is not within

I'm working with JavaFX and trying to incorporate a CSS file into my scene.

scene.getStyleSheets().add(Main.class.getResource("res/application.css").toExternalForm();

An NPE is being thrown. I suspect it's because the css file isn't located within the classpath. But I'm unsure how to tackle loading it in this manner. I prefer not to have the css file in my package directory (com.somecompany.package). Instead, I'd like it to be in a separate directory for independent deployment (allowing users to modify if needed).

Is there a way to load a css file (or any resource) from outside the classpath?

Here is my stack trace:

java.lang.NullPointerException
        at com.somecompany.someapp.Main.start(Main.java:30)
        at com.sun.javafx.application.LauncherImpl$5.run(LauncherImpl.java:319)
        at com.sun.javafx.application.PlatformImpl$5.run(PlatformImpl.java:206)
        at com.sun.javafx.application.PlatformImpl$4.run(PlatformImpl.java:173)
        at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
        at com.sun.glass.ui.win.WinApplication.access$100(WinApplication.java:29)
        at com.sun.glass.ui.win.WinApplication$3$1.run(WinApplication.java:73)
    at java.lang.Thread.run(Unknown Source)
javacssjavafxclasspath

Answer №1

To search for a resource at the root of the classpath, add a / at the beginning of the String argument.

scene.getStyleSheets().add(Main.class.getResource("/res/application.css").toExternalForm();

If not using the root path, the resource is resolved relative to the package that contains Main. Details on how resources are resolved can be found in the javadoc.

If you need to modify the file, it's best to get it from the file system instead.

Path path = Paths.get("/path/to/file");     
scene.getStyleSheets().add(path.toUri().toURL()).toExternalForm();

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