手机存储分为三块区域
1.内部存储
2.SD卡存储（Primary External Storage）
3.外置sd卡（Secondary External Storage）

内部存储

1.RAM 运行时内存
2.ROM 内部存储,即data目录

*Environment.getDataDirectory().getPath()
/data（没有root，无法打开）

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1.app（存放着安装的apk）
2.data（APP的存储内容）
data/data/<包名>/shared_prefs
data/data/<包名>/databases
data/data/<包名>/files
data/data/<包名>/cache（context.getCacheDir()）
3.mnt(挂载点)
4.dev（Linux系统文件夹）
5.system（系统配置）

Environment.getDownloadCacheDirectory().getPath()
/cache
Environment.getRootDirectory().getPath()
/system*

SD卡存储（可读写）

外部存储路径：
Environment.getExternalStorageDirectory().getPath()
/storage/emulated/0

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九大公有目录：

Environment.getExternalStoragePublicDirectory(DIRECTORY_ALARMS) ;
//storage/emulated/0/Alarms
Environment.getExternalStoragePublicDirectory(DIRECTORY_DCIM);
//storage/emulated/0/DCIM
Environment.getExternalStoragePublicDirectory(DIRECTORY_DOWNLOADS);
//storage/emulated/0/Download
Environment.getExternalStoragePublicDirectory(DIRECTORY_MOVIES);
//storage/emulated/0/Movies
Environment.getExternalStoragePublicDirectory(DIRECTORY_MUSIC);
//storage/emulated/0/Music
Environment.getExternalStoragePublicDirectory(DIRECTORY_NOTIFICATIONS);
//storage/emulated/0/Notifications
Environment.getExternalStoragePublicDirectory(DIRECTORY_PICTURES);
//storage/emulated/0/Pictures
Environment.getExternalStoragePublicDirectory(DIRECTORY_PODCASTS);
//storage/emulated/0/Podcasts
Environment.getExternalStoragePublicDirectory(DIRECTORY_RINGTONES);
//storage/emulated/0/Ringtones
可通过context.getExternalFilesDir(String type)获取，也由上直接获取，不建设使用公有目录存储App数据

私有目录：

getExternalCacheDir()
//storage/emulated/0/Android/data/<包名>/cache/

context.getObbDir()
//storage/sdcard/Android/obb/

外置SD卡（可读，无法写入）

public static String getExtendedMemoryPath(Context mContext) {
    StorageManager mStorageManager = (StorageManager) mContext.getSystemService(Context.STORAGE_SERVICE);
    try {
        Class<?> storageVolumeClazz = Class.forName("android.os.storage.StorageVolume");
        Object result = null;
        if (mStorageManager != null){
            Method getVolumeList = mStorageManager.getClass().getMethod("getVolumeList");
            result = getVolumeList.invoke(mStorageManager);
        }
        Method getPath = storageVolumeClazz.getMethod("getPath");
        Method isRemovable = storageVolumeClazz.getMethod("isRemovable");
        final int length = Array.getLength(result);
        for (int i = 0; i < length; i++) {
            Object storageVolumeElement = Array.get(result, i);
            String path = (String) getPath.invoke(storageVolumeElement);
            boolean removable = (Boolean) isRemovable.invoke(storageVolumeElement);
            if (removable) {
                return path;
            }
        }
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (InvocationTargetException e) {
        e.printStackTrace();
    } catch (NoSuchMethodException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    }
    return null;
}

应用管理清除数据的清楚目录：

清除缓存：将外部私有数据下的cache包（/storage/emulated/0/Android/data/<包名>/cache）清除，将内部数据下的cache包下的内容（/data/data/<包名>/cache/）清除 。
清楚数据：将外部私有数据的data下包名（/storage/emulated/0/Android/data/<包名>/）清除，将内部数据包名下的所有内容（/data/data/<包名>/）清除；