FileChooser fileChooser = new FileChooser();
 FileChooser.ExtensionFilter extFilter = new FileChooser.ExtensionFilter("PDF file(*.pdf)" ,"
 *.pdf");

 fileChooser.getExtensionFilters().add(extFilter);
 extFilter = new FileChooser.ExtensionFilter("PNG files (*.png)", "*.png");
 fileChooser.getExtensionFilters().add(extFilter);
 fileChooser.setTitle("Save as");
 File file = fileChooser.showSaveDialog(primaryStage);

String filePath = file.getAbsolutePath();

String fileName = file1.getName();
String fileExtension = fileName.substring(fileName.lastIndexOf(".") + 1, file1.getName().length());
System.out.println(">> fileExtension" + fileExtension);

FileChooser fileChooser = new FileChooser();
// Set extension filter
FileChooser.ExtensionFilter extFilter = new FileChooser.ExtensionFilter("Image Files", "*.jpg", "*.jpeg");
fileChooser.getExtensionFilters().add(extFilter);

File file = fileChooser.showOpenDialog(root.getScene().getWindow());

if (file != null) {

String fileName = file.getName();
String fileExtension = fileName.substring(fileName.lastIndexOf(".") + 1, file.getName().length());
System.out.println(">> fileExtension" + fileExtension);

}

FileChooser fc = new FileChooser();
fc.setInitialFileName("Exported.txt");
fc.getExtensionFilters().add(new FileChooser.ExtensionFilter("Text Files (*.txt)", "*.txt"));
fc.getExtensionFilters().add(new FileChooser.ExtensionFilter("XML Files (*.xml)", "*.xml"));
fc.getExtensionFilters().add(new FileChooser.ExtensionFilter("All Files (*.*)", "*"));
File file = fc.showSaveDialog(rootPane.getScene().getWindow());
if (file != null)
{
    File f;
    String tempPath = file.getCanonicalPath().toLowerCase();
    if (!(tempPath.endsWith(".txt") || tempPath.endsWith(".xml")))
    {
        String extension = fc.selectedExtensionFilterProperty().get().getExtensions().get(0).substring(1);
        // default to .txt, if the user had *.* selected
        if (extension.length() == 0)
        {
            extension = ".txt";
        }
        f = new File(file.getCanonicalPath() + extension);
    }
    else
    {
        f = file.getCanonicalFile();
    }

    System.out.println(f);
    if (f.exists())
    {
        System.err.println("You will overwrite!");
    }
}