why sometime it throws FileNotFoundException

Question

The code works for most of the time, but some time it throws exception. Couldn't figure out what could cause it.

What is does is to create a file at

/storage/emulated/0/Download/theFileName.jpg

and write data to it (from sourceFile which does exist), but got "file not exist" exception for the newly created file.

(it does have uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE", and uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" in manifest).

File sourceFile = new File(theSourceFileFullPath);
if (sourceFile.exists()) {
    File downloadDirectory = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);
    String downloadPath = downloadDirectory.getPath();
    String newFilePath = (downloadPath + "/" + fileName);
    File newFile = new File(newFilePath);
    try {
        FileInputStream in = new FileInputStream(sourceFile);

        // ava.io.FileNotFoundException: 
        //     /storage/emulated/0/Download/theFileName.jpg: open failed: ENOENT (No such file or directory) 
        // exception at this line       
        FileOutputStream out = new FileOutputStream(newFile);
        //......
     } catch (Exception e) {}
}

Answer 1

I can think of the following possible reasons for this behavior:

1. The new file could not be created simply because there is no free space on SD card. The next time you encounter this issue, try to see if you have at least some available space via file manager or Settings -> Storage. I doubt you can do something about it if this is what happens on your user's device.
2. The SD card is not available due to some OS glitch or it's physically not attached, thus the file could not be created. Once again - there is nothing you can do about it, other than showing some Toast with error message.
3. How do you generate the fileName part of your file's path? Sometimes the files can not be created because the filename contains unsupported (by this particular device) characters. E.g. I have HTC Desire X with Android 4.1.2 which can not create files with the code similar to yours if the filename contains colon. Try another way to generate the filename and see if it makes a difference.

4. Did you make sure that the Downloads directory exists before creating the file inside it? Write something like the following:

   if (!downloadDirectory.exists()) {
       downloadDirectory.mkdirs();
   }
   

5. The WRITE_EXTERNAL_STORAGE permission is considered dangerous on the Android 6, thus it can be revoked by the user at any time. Make sure user didn't revoke this permission before writing to the file.

6. Always close the I/O stream when you finished working with it. Add the finally clause to your try-catch block and close both in and out streams in it:

   finally {
       if (in != null) {
           try {
               in.close();
           } catch (Exception e) { }
       }
   
       if (out != null) {
           try {
               out.close();
           } catch (Exception e) { }
       }
   }
   

7. The last one - and finally I'm out of options. :) I suppose this issue could also arise if you write to the same file from multiple threads. If that's the case, try to synchronize access to your file-writing code.