android之ROM和sd卡

rom路径：

// File file = new File("/data/data/cn.itcast.file/files/"+filename);
// FileInputStream fis = new FileInputStream(file);

FileInputStream fis = context.openFileInput(filename);

sd卡路径
// File file = new File("/mnt/sdcard/", filename);
File file = new File(Environment.getExternalStorageDirectory(),filename);

细节：为增强程序健壮性，在使用sd卡存储前先判断sd卡状态
sd卡是否安装
if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()))
此处用到一个权限：
<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>

读写sd卡要权限
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>