static java.io.File virtual_newFile(String path) {
  return new java.io.File(virtual_rebase(path));
}

static java.io.FileInputStream virtual_newFileInputStream(String path) {
  return new java.io.FileInputStream(virtual_rebase(path));
}

static java.io.FileInputStream virtual_newFileOutputStream(String path) {
  return new java.io.FileOutputStream(virtual_rebase(path));
}

static String virtual_baseDir = "";

static String virtual_rebase(String path) {
  if (new File(path).isAbsolute())
    return path;
  else
    return new File(new File(virtual_baseDir), path).getPath();
}

Began life as a copy of #2000345