Android Studio – Android assets no such file or directory

In my android project I have created an assets folder in which I have added some json files and I want to read them with a stringBuffer. The assets folder is listed inside src/main. So far I have added the following code:

   String[] files = assetManager.list("");
   ArrayList<String> it = new ArrayList<>(Arrays.asList(files)); 

And so far I am getting the names of the files successfully inside my ArrayList. Then I am trying this:

InputStream input = assetManager.open("filename.json");

But I get the following error:

Failed to open file

‘/data/data/package/code_cache/.overlay/base.apk/assets/filename.json’:
No such file or directory

I also have included the follwing permission in the manifest:

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

Any idea what might be the problem here?