File Chooser

Controller.java

package sample;

import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.TextArea;
import javafx.scene.input.MouseEvent;
import javafx.stage.FileChooser;
import javafx.stage.Stage;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.net.URL;
import java.util.ResourceBundle;
import java.util.Scanner;

public class Controller implements Initializable {

    FileChooser fileChooser = new FileChooser();

    @FXML
    private TextArea textArea;
    
    //Added null check to check rather a file is picked or not
    @FXML
    void getText(MouseEvent event) {
        File file = fileChooser.showOpenDialog(new Stage());

        if(file != null){
            try {
                Scanner scanner = new Scanner(file);
                while(scanner.hasNextLine()){
                    textArea.appendText(scanner.nextLine() + "\n");
                }
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
        }
    }

    @FXML
    void save(MouseEvent event) {
        File file = fileChooser.showSaveDialog(new Stage());
        if(file != null){
            saveSystem(file, textArea.getText());
        }
    }

    @Override
    public void initialize(URL url, ResourceBundle resourceBundle) {
        fileChooser.setInitialDirectory(new File("C:\\Software\\FileChooser\\src\\sample"));
    }

    public void saveSystem(File file, String content){
        try {
            PrintWriter printWriter = new PrintWriter(file);
            printWriter.write(content);
            printWriter.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }

    }
}

Main.java

package sample;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

import java.io.File;
import java.io.IOException;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
        primaryStage.setTitle("Hello World");
        primaryStage.setScene(new Scene(root));
        primaryStage.show();
    }


    public static void main(String[] args) {
        File file = new File("src\\sample\\text.txt");
        try {
            file.createNewFile();
        } catch (IOException e) {
            e.printStackTrace();
        }
        launch(args);
    }
}

Sample.fxml

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.Button?>
<?import javafx.scene.control.TextArea?>
<?import javafx.scene.layout.AnchorPane?>


<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/15.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
   <children>
      <Button layoutX="79.0" layoutY="93.0" mnemonicParsing="false" onMouseClicked="#getText" prefHeight="66.0" prefWidth="144.0" text="GetText" />
      <TextArea fx:id="textArea" layoutX="300.0" layoutY="93.0" prefHeight="215.0" prefWidth="242.0" />
      <Button layoutX="89.0" layoutY="214.0" mnemonicParsing="false" onMouseClicked="#save" prefHeight="78.0" prefWidth="125.0" text="Save" />
   </children>
</AnchorPane>