How to reference javafx fxml files in resource folder?

Generic Resource Lookup Information

This answer discusses FXML location lookup, which is really just a subset of the generic resource lookup task in Java. The resource location is passed by the calling program as input to the FXMLLoader, so the resource lookup itself is part of your calling application code and not the FXMLLoader.

For thorough coverage of generic resource information (including recommended troubleshooting steps) for Java/JavaFX applications, please refer to:

• How do I determine the correct path for FXML files, CSS files, Images, and other resources needed by my JavaFX Application?

Also useful, is the Eden coding resource guide:

• Where to put resource files in JavaFX

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Example usage

FXMLLoader loader = new FXMLLoader();
loader.setLocation(getClass().getResource("/main.fxml"));
Parent content = loader.load(); 

Location resolution options

1. Put all of your fxml in the src/main/resources directory.

   loader.setLocation(getClass().getResource("/main.fxml"));
   

2. Put all of your fxml in a src/main/resources/fxml directory.

   loader.setLocation(getClass().getResource("/fxml/main.fxml"));
   

3. Place fxml in a corresponding resource directory; e.g. src/main/resources/com/mycompany/myapp.

   loader.setLocation(getClass().getResource("main.fxml")); 
   

The last option assumes that the class from which you are loading the fxml is in the same relative location in the corresponding Java source hierarchy. For example, you might invoke the last load command from source com/mycompany/myapp/Main.java.

FXMLLoader usage recommendations

1. Instantiate an FXMLLoader via new FXMLLoader() rather than using
   the static methods on the FXMLLoader.

   • The static methods
     become confusing when you want to get values (like instantiated
     controllers) out of a loader.

2. Set the location on the instantiated FXMLLoader and call
   load() rather than loading from a stream using
   load(stream).

   • Setting a URL based location on the loader allows for resolution of
     relative resources loaded in fxml and css files. Relative
     resources do not resolve for a stream based constructor.

3. To derive a location based upon a class, use
   getClass().getResource(), as it is URL based, rather than
   getClass().getResourceAsStream() which is stream based.

IDE and Build Settings

Ensure that your IDE or build tool is copying the fxml files from the resource directory to the build output directory. For understanding Intellij settings for this, see: How to convert a normal java project in intellij into a JavaFx project.

A note on Java Jigsaw modular applications

See:

• How to access resource using class loader in Java 9

Specifically, don’t write:

ComboBoxStyling.class.getClassLoader()
    .getResource("/css/styleclass.css");

Instead write:

ComboBoxStyling.class
    .getResource("/css/styleclass.css"); 

That is, get the resource from the class directly rather, NOT from the class loader. If you get resources from a class loader rather than the class, then there are additional restrictions on lookup based upon the module configuration. These restrictions can be hard to understand, see the documentation for the Class and ClassLoader getResource methods for information if needed.