一些路径的标准写法
Environment.getDataDirectory() = /data
Environment.getDownloadCacheDirectory() = /cache
Environment.getExternalStorageDirectory() = /mnt/sdcard
Environment.getRootDirectory() = /system
context.getCacheDir() = /data/data/com.mt.mtpp/cache
context.getExternalCacheDir() = /mnt/sdcard/Android/data/com.mt.mtpp/cache
context.getFilesDir() = /data/data/com.mt.mtpp/files