Java Swing - 如何解决JEditorPane的外部资源

import java.awt.Dimension;
import java.io.File;

import javax.swing.JEditorPane;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;

public class Main {

  public static void main(String[] args) throws Exception {
    File f = new File("index.html");
    JEditorPane jep = new JEditorPane(f.toURI().toURL());

    JScrollPane sp = new JScrollPane(jep);
    sp.setPreferredSize(new Dimension(400, 200));

    JOptionPane.showMessageDialog(null, sp);
  }
}