How to get FileInputStream to File in assets folder

Question

I know how to use the AssetManager to read a File from the res/raw directory with an InputStream, but for my special use case I need a FileInputStream. The reason I need a FileInputStream specifically is because I need to get the FileChannel object from it by calling getChannel().

This is the code I have so far, it reads the data (in my case a list of primitives) from a File:

public static int[] loadByMappedBuffer(Context context, String filename) throws IOException{
    FileInputStream fis = context.openFileInput(filename);
    FileChannel ch = fis.getChannel();

    MappedByteBuffer mbuff = ch.map(MapMode.READ_ONLY, 0, ch.size());
    IntBuffer ibuff = mbuff.asIntBuffer();

    int[] array = new int[ibuff.limit()];
    ibuff.get(array);

    fis.close();
    ch.close();

    return array;
}

I had tried to create File from an Uri, but that just results in a FileNotFoundException:

Uri uri = Uri.parse("android.resource://com.example.empty/raw/file");
File file = new File(uri.getPath());
FileInputStream fis = new FileInputStream(file);

Is there a way I can get a FileInputStream to a File in the res/raw directory?

I think your URL is the problem.And you should add from the assets directory. — Kristy Welsh, May 20 '15 at 15:41
So all you need is to read file contents as int array? Am I correct? — Ayzen, May 20 '15 at 15:41
@Ayzen yes, but I need to make it fast, method, that I gave reads 80K*4 bytes and transform it to int array by 6-7 ms on my PC — Mike Herasimov, May 20 '15 at 15:44
@KristyWelsh I also had tried `Uri uri = Uri.parse("android.resource://com.example.empty/" + R.raw.file);` — Mike Herasimov, May 20 '15 at 15:45
Try this: InputStream myInput = myContext.getAssets().open(YOUR_FILE_NAME) — Kristy Welsh, May 20 '15 at 15:47
@KristyWelsh I need `FileInputStream` and I don't work with DB, I'm working with text file — Mike Herasimov, May 20 '15 at 15:48
@MichaelHerasimov - I updated my comment - and you just need to be able to read from the file, right? — Kristy Welsh, May 20 '15 at 15:48
FileInputStream myfileInput = getResources().getAssets().open(FILE_NAME); Will work. — Kristy Welsh, May 20 '15 at 15:51
@KristyWelsh I'm "just" need to be able transform this code for Android — Mike Herasimov, May 20 '15 at 15:53
@KristyWelsh I mean I had gave code that reads file from `files` directory and I need to read file by this method from `raw` directory — Mike Herasimov, May 20 '15 at 15:56
getResources().getAssets().open() doesn't return FileInputStream. It returns AssetInputStream. — Ayzen, May 20 '15 at 16:00
@Ayzen and there are a way to get `FileInputStream` from `AssetInputStream`? — Mike Herasimov, May 20 '15 at 16:02
It seems the only way to read your data is using InputStream... — Ayzen, May 20 '15 at 16:13
@ChrisStratton but how to deal wiyh `nio` when I have `InputStream`? — Mike Herasimov, May 20 '15 at 16:16
You don't need to for this. Focus on the problem, which appears to be reading an array of ints from an InputStream. You don't need a MappedByteBuffer for that. — Chris Stratton, May 20 '15 at 16:30
Related problem: http://stackoverflow.com/questions/30395744/filechannel-returns-wrong-file-size-of-file-in-assets-folder — Xaver Kapeller, May 22 '15 at 13:02

Xaver Kapeller · Accepted Answer · 2015-05-22T13:56:13.637

26

You can get a FileInputStream to a resource in your assets like this:

AssetFileDescriptor fileDescriptor = assetManager.openFd(fileName);
FileInputStream stream = fileDescriptor.createInputStream();

The fileName you supply to openFd() should be the relative path to the asset, the same fileName you would supply to open().

Alternatively you can also create the FileInputStream like this:

AssetFileDescriptor assetFileDescriptor = assetManager.openFd(fileName);  
FileDescriptor fileDescriptor = assetFileDescriptor.getFileDescriptor();  
FileInputStream stream = new FileInputStream(fileDescriptor);

edited May 22 '15 at 13:56

answered May 20 '15 at 16:59

Xaver Kapeller

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4

You can use `getAssets()` to get assetManager – Amr Ashraf Jun 27 '20 at 21:08

score 1 · Answer 2 · answered Sep 22 '21 at 08:28

small tweeking in "@Xaver Kapeller" answer:
if u don't get "assetManager" use "ctx.getAssets()" instead;

AssetFileDescriptor assetFileDescriptor = ctx.getAssets().openFd(fileName);  
FileDescriptor fileDescriptor = assetFileDescriptor.getFileDescriptor();  
FileInputStream stream = new FileInputStream(fileDescriptor);

How to get FileInputStream to File in assets folder

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