Android私有数据内部存储方法

      本节介绍这个存储私有数据的 API，它使用 android.content.Context.openFileInput、openFileOutput 和 getCacheDir() 来高速缓存数据，当用户卸载掉应用程序时，这些文件就会被移除。

• 存储数据至内部私有存储器:

/**
 * Writes content to internal storage making the content private to 
 * the application. The method can be easily changed to take the MODE 
 * as argument and let the caller dictate the visibility: 
 * MODE_PRIVATE, MODE_WORLD_WRITEABLE, MODE_WORLD_READABLE, etc.
 * 
 * @param filename - the name of the file to create
 * @param content - the content to write
 */
public void writeInternalStoragePrivate(
        String filename, byte[] content) {
    try {
        //MODE_PRIVATE creates/replaces a file and makes 
        //  it private to your application. Other modes:
        //    MODE_WORLD_WRITEABLE
        //    MODE_WORLD_READABLE
        //    MODE_APPEND
        FileOutputStream fos = 
           openFileOutput(filename, Context.MODE_PRIVATE);
        fos.write(content);
        fos.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
} 

• 读取数据：

/**
 * Reads a file from internal storage
 * @param filename the file to read from
 * @return the file content
 */
public byte[] readInternalStoragePrivate(String filename) {
    int len = 1024;
    byte[] buffer = new byte[len];
    try {
        FileInputStream fis = openFileInput(filename);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        int nrb = fis.read(buffer, 0, len); // read up to len bytes
        while (nrb != -1) {
            baos.write(buffer, 0, nrb);
            nrb = fis.read(buffer, 0, len);
        }
        buffer = baos.toByteArray();
        fis.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return buffer;
}

• 删除数据：

/**
 * Delete internal private file 
 * @param filename - the filename to delete
 */
public void deleteInternalStoragePrivate(String filename) {
    File file = getFileStreamPath(filename);
    if (file != null) {
        file.delete();
    }
}