What is the best way to download files and save them to different folders within the android assets? [closed]

You can not save a file inside the assets folder after it has already been packaged and generated the APK because it is read-only. See the Android documentation existing storage options .

However, if you want to check if a file already exists within assets before downloading another folder, it would be possible through the filename . For example, see this method below in which you are checking whether a file already exists within assets by passing the context and a specific name as a parameter:

public static boolean existFileInAsset(Context context, String file) {
    try {
        InputStream stream = context.getAssets().open("file:///android_asset/" + file);
        stream.close();
        return true;
    } catch (IOException e) {
       return false;
    }
}  

So, just check this way below:

if(existFileInAsset(context,"jonsnow.pdf")){
    // aqui exibe qualquer mensagem considerando que o arquivo existe
} else {
    // aqui você pode colocar algum código para fazer download do arquivo 
    // pois se entrou aqui, é porque não existe o arquivo salvo com este nome.
}

No Kotlin would look like this:

fun existFileInAsset(context: Context, file: String): Boolean {
    try {
        val stream = context.assets.open("file:///android_asset/" + file)
        stream.close()
        return true
    } catch (e: IOException) {
        return false
    }
}

To use this function in Kotlin, follow the same logic as JAVA.