java读取文件内容为string字符串的方法

/**
 * 读出城市列表文件
 */
 private String readCityFile() {
  File file02 = new File(path_xinfu, "/cityList.json");
  FileInputStream is = null;
  StringBuilder stringBuilder = null;
  try {
   if (file02.length() != 0) {
    /**
     * 文件有内容才去读文件
     */
    is = new FileInputStream(file02);
    InputStreamReader streamReader = new InputStreamReader(is);
    BufferedReader reader = new BufferedReader(streamReader);
    String line;
    stringBuilder = new StringBuilder();
    while ((line = reader.readLine()) != null) {
     // stringBuilder.append(line);
     stringBuilder.append(line);
    }
    reader.close();
    is.close();
   } else {
    mLoadingLayout.setStatus(LoadingLayout.Empty);
   }

  } catch (Exception e) {
   e.printStackTrace();
  }
  return String.valueOf(stringBuilder);

 }