思路

采用文件形式存储JSON数据。将网络请求出的JSON数据，解析成String，然后使用字符流读、写。

公司项目中以前使用的是ObjectInputStream和ObjectOutputStream这样的对象字节流来读、写，效率较字符流比 —— 较低

将JSON-String 缓存到文件

首先获取Android上可用的缓存目录；之后，字符流写入

public static void writeJson(Context c, String json, String fileName) {
   File cacheRoot = TextUtils.equals(Environment.getExternalStorageState(), (Environment.MEDIA_MOUNTED)) ? c.getExternalCacheDir() : c.getCacheDir();
   BufferedWriter writer = null;
   try {
      File file = new File(cacheRoot, fileName);
      writer = new BufferedWriter(new FileWriter(file));
      writer.write(json);
      writer.flush();
   } catch (Exception e) {
      e.printStackTrace();
   } finally {
      IOUtil.close(writer);
   }
}

读取JSON-String 缓存文件

字符流读取

public static StringBuilder readJson(Context c, String fileName) {
  return readJson(c, fileName, 24 * 3600 * 1000L);//指定缓存1天将过期
}
/**
 * @param expireTime 缓存过期的时间毫秒值
 */
public static StringBuilder readJson(Context c, String fileName, long expireTime) {
  File cacheRoot = TextUtils.equals(Environment.getExternalStorageState(), (Environment.MEDIA_MOUNTED)) ? c.getExternalCacheDir() : c.getCacheDir();
  StringBuilder builder = new StringBuilder();
  BufferedReader reader = null;
  try {
    File file = new File(cacheRoot, fileName);
    if (!isValid(file, expireTime)) return builder;
    reader = new BufferedReader(new FileReader(file));
    String line;
    while ((line = reader.readLine()) != null) {
      builder.append(line);
    }
  } catch (Exception e) {
    e.printStackTrace();
  } finally {
    IOUtil.close(reader);
  }
  return builder;
}
/**
 * 验证文件是否有效
 * @param f
 * @param timeout
 * @return  true: 表示有效
 */
private static boolean isValid(File f, long timeout) {
  if (f == null || !f.exists()) return false;
  if (timeout <= 0) return true;
  if (System.currentTimeMillis() - f.lastModified() > timeout) {//已过期
    f.deleteOnExit();
    return false;
  }
  return true;
}