My app can create a file, but cannot read it

Question

I write a file in internal memory:

byte[] data = ... // (A buffer containing wav data)
String filename = context.getFilesDir().getAbsolutePath() + "/newout.wav";
File file = new File(filename);
FileOutputStream fos = new FileOutputStream(file);
fos.write(data);
fos.close();

Then I try to play it:

MediaPlayer player = new MediaPlayer();
player.setDataSource(filename);
player.prepare();
player.setLooping(false);
player.start();

But the prepare() fails:

java.io.IOException: Prepare failed.: status=0x1

I checked the file and saw that it's permission is -rw-------. I changed it to -rw-r--r--, after that it was being played successfully.

So how come my app can write a file, but can't read it? And how can I make the FileOutputStream to set the permissions right?

I think you are writing file in internal memory, please check the path — Sameer Z., Apr 30 '15 at 13:01
It is in internal memory: `/data/data/xx.xxx.xxx/files/newout.wav` — Mousa, Apr 30 '15 at 13:17
check this http://stackoverflow.com/questions/4833777/android-playing-resource-files-from-internal-storage-causes-mediaplayer-prepare — Sameer Z., Apr 30 '15 at 13:22
Oh! So the problem is in `MediaPlayer`! Maybe it uses another process to play and that causes problems. Thanks Sameer :) — Mousa, Apr 30 '15 at 13:40

score 2 · Accepted Answer · answered Apr 30 '15 at 13:04

2

To change programaticaly the file permissions to -rw-r--r-- you need to do smoething like this:

Process process = null;
DataOutputStream dataOutputStream = null;

try {
    process = Runtime.getRuntime().exec("su");
    dataOutputStream = new DataOutputStream(process.getOutputStream());
    dataOutputStream.writeBytes("chmod 644 FilePath\n");
    dataOutputStream.writeBytes("exit\n");
    dataOutputStream.flush();
    process.waitFor();
} catch (Exception e) {
    return false;
} finally {
    try {
        if (dataOutputStream != null) {
            dataOutputStream.close();
        }
        process.destroy();
    } catch (Exception e) {
        System.out.println(e.getMessage());
    }
}

answered Apr 30 '15 at 13:04

Gabriella Angelova

2,985
1
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OK, this helps, but judging from the use of `su`, it needs root privileges, right? – Mousa Apr 30 '15 at 13:25
yes, you need to be with administrator's permissions on your machine – Gabriella Angelova Apr 30 '15 at 13:57
1

Well I used this approach, but since I own that file, I didn't even need `su`! – Mousa Apr 30 '15 at 14:11
That's super, so you could use it more easily :) – Gabriella Angelova Apr 30 '15 at 14:12
However can I rely on `chmod` to be available in every Android device? – Mousa Apr 30 '15 at 14:14
I think yes, but if someone has another experience, please correct me – Gabriella Angelova Apr 30 '15 at 14:16

score 1 · Answer 2 · answered Apr 30 '15 at 13:08

1

If you open a file, the default mode is Context.MODE_PRIVATE, e.g. as in

File file = new File(context.getFilesDir(), filename);

String filename = "myfile";
String string = "Hello world!";
FileOutputStream outputStream;

try {
  outputStream = openFileOutput(filename, Context.MODE_PRIVATE);
  outputStream.write(string.getBytes());
  outputStream.close();

} catch (Exception e) {
  e.printStackTrace();
}

(taken from the documentation). Modes MODE_WORLD_READABLE and MODE_WORLD_WRITABLE are deprecated and do not work on newer devices. So I'd say you should rather write on the external storage to make contents available to other apps.

Note: as per documentation:

External storage: "It's world-readable, so files saved here may be read outside of your control."

answered Apr 30 '15 at 13:08

Trinimon

13,839
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I'm not trying to make it available to other apps! Both the writing and reading takes place in the same app. – Mousa Apr 30 '15 at 13:22
changing to `MODE_WORLD_READABLE` made it readable, but I wonder why `rw-------` is not enough when it's in the same app?! – Mousa Apr 30 '15 at 13:31
As far as I remember all apps run as their own user and the permissions you mentioned above allow only your app to write and read. The _MediaPlayer_ however, is part of another app running as another user that has no access rights per default. Once you extended the permission to `-rw-r--r--`, all users have the right to read (including the systems _MediaPlayer_) **p.s.:** take care with `MODE_WORLD_READABLE` - it might not always work – Trinimon Apr 30 '15 at 13:34
1

Yes, as the link Sameer provided, the main problem is in `MediaPlayer`. Since I don't like using deprecated things, I used Gabriella's approach to change permissions to prepare file for `MediaPlayer`. – Mousa Apr 30 '15 at 14:13
Gabriella's approach is just perfect for rooted phones ... :) – Trinimon Apr 30 '15 at 17:10
1

Yes, but since my app owns that file, I just execute `chmod` without `su`. – Mousa Apr 30 '15 at 17:19

My app can create a file, but cannot read it

2 Answers2