JFileChooser 选择目录，选择保存路径，并对保存文件类型进行更改:

 JFileChooser :

//选择目录
  JFileChooser chooser = new JFileChooser();
  chooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
  int result = chooser.showOpenDialog(null);
  String fname = chooser.getName(chooser.getSelectedFile());
  if (result == JFileChooser.APPROVE_OPTION) {

   String filePath = chooser.getSelectedFile().getPath();
   System.out.println(filePath);
  }

//保存文件：

  JFileChooser fd = new JFileChooser();
  HtmlFileFilter hff = new HtmlFileFilter();
  fd.addChoosableFileFilter(hff);
  fd.showSaveDialog(null);
  File f = fd.getSelectedFile();
  if (f != null){
   System.out.println(f.getAbsolutePath() + ".html");
   jTextField2.setText(f.getAbsolutePath() + ".html");
  }

过滤器：

class HtmlFileFilter extends FileFilter {
 public String getDescription() {
  return "*.html(网页文件)";
 }

 public boolean accept(File file) {
  String name = file.getName();
  return name.toLowerCase().endsWith(".html");
 }
}