JFileChooser chooser = new JFileChooser(".");
chooser.setMultiSelectionEnabled(true);
chooser.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);
int ret = chooser.showOpenDialog(null);
if(ret == JFileChooser.APPROVE_OPTION) {
    File[] files = chooser.getSelectedFiles();
    ...
}