How to set default value for javafx DatePicker in FXML?

To instantiate java.time.LocalDate from an FXML file, you need to create and register a custom builder for the class.

• Create a builder for LocalDate. The builder must implement javafx.util.Builder and its build method. Here's an example builder that takes three parameters (year, month, dayOfMonth):

  package util;
  import java.time.LocalDate;
  import javafx.util.Builder;
  
  public class LocalDateBuilder implements Builder<LocalDate>{
  
      private int year;
      private int month;
      private int dayOfMonth;
  
      @Override
      public LocalDate build() {
          return LocalDate.of(year, month, dayOfMonth);
      }
  
      public int getYear() {
          return year;
      }
      public void setYear(int year) {
          this.year = year;
      }
      public int getMonth() {
          return month;
      }
      public void setMonth(int month) {
          this.month = month;
      }
      public int getDayOfMonth() {
          return dayOfMonth;
      }
      public void setDayOfMonth(int dayOfMonth) {
          this.dayOfMonth = dayOfMonth;
      }
  }
  
        
  
          
          
          
        
  
      

• Create a FactoryBuilder wrapper that will decorate the default FactoryBuilder so that it returns your builder when a LocalDate builder is needed. Here is an example of a FactoryBuilderWrapper class.

  package util;
  import java.time.LocalDate;
  import javafx.util.Builder;
  import javafx.util.BuilderFactory;
  
  public class BuilderFactoryWrapper implements BuilderFactory {
  
      private BuilderFactory builderFactory;
      public BuilderFactoryWrapper(BuilderFactory builderFactory) {
          this.builderFactory = builderFactory;
      }
  
      @Override
      public Builder<?> getBuilder(Class<?> klass) {
          if (klass == LocalDate.class) {
              // return our builder
              return new LocalDateBuilder();
          } else {
              // return the default builder
              return builderFactory.getBuilder(klass);
          }
      }
  }
  
        
  
          
          
          
        
  
      

• In your application startup method, get the default FactoryBuilder, wrap it in your wrapper and reassign it to FXMLLoader:

  @Override
  public void start(Stage stage) throws Exception {
      FXMLLoader loader = new FXMLLoader();
      loader.setLocation(getClass().getResource("myUI.fxml"));
      BuilderFactory builderFactory = loader.getBuilderFactory();
      // wrap the default BuilderFactory
      loader.setBuilderFactory(new    
              BuilderFactoryWrapper(builderFactory));
  
      Parent root = loader.load();
      Scene scene = new Scene(root);
      stage.setScene(scene);
      stage.show();
  }
  
        
  
          
          
          
        
  
      

Below is the FXML code to create a Person with a birthDate property of type LocalDate: (you need to import java.time.LocalDate, but not the builder itself)

<?import model.Person?>
<?import java.time.LocalDate?>
...
<Person firstName="Jane" lastName="Citizen">
    <birthDate>
        <LocalDate year="1980" month="12" dayOfMonth="19"/>
    </birthDate>
</Person>