MainActivity.kt

//Fetching the local styles JSON file from the assets 
val styleJsonInputStream = assets.open("bright.json")

//Creating a new file to which to copy the json content to
val dir = File(filesDir.absolutePath)
val styleFile = File(dir, "bright.json")
//Copying the original JSON content to new file
copyStreamToFile(styleJsonInputStream, styleFile)

//Getting reference to mbtiles file in assets
val mbtilesFile = getFileFromAssets(this, "india_coimbatore.mbtiles")
val bounds = getLatLngBounds(mbtilesFile)

//Replacing placeholder with uri of the mbtiles file
val newFileStr = styleFile.inputStream().readToString()
    .replace("___FILE_URI___", "mbtiles:///${mbtilesFile.absolutePath}")

//Writing new content to file
val gpxWriter = FileWriter(styleFile)
val out = BufferedWriter(gpxWriter)
out.write(newFileStr)
out.close()

//Setting the map style using the new edited JSON file 
map.setStyle(Style.Builder().fromUri(Uri.fromFile(styleFile).toString()))
//Setting camera view over the mbtiles area
map.animateCamera(CameraUpdateFactory.newLatLngBounds(bounds, 50))