How to play mp3 files from internal and external SD card in android?

I am working on a mp3 player app, which plays .mp3 files present anywhere inside an internal SD card.

I have used the following codes to fetch the .mp3 files present in internal storage.

ArrayList<File> inFiles = new ArrayList<File>();
File list[] = file.listFiles();
//Log.i("DIR", "PATH" +file.getPath());
for (int i = 0; i < list.length; i++) 
{
    // myList.add( list[i].getName() );
    File temp_file = new File(file.getAbsolutePath(),list[i].getName());
    //Log.i("DIR", "PATH" +temp_file.getAbsolutePath());
    if (temp_file.listFiles() != null) 
    {
        //Log.i("inside", "call fn");
        listfiles(temp_file);

    }
    else 
    {
        if (list[i].getName().toLowerCase().contains(".mp3"))
        {
            inFiles.add(list[i]);
        //Log.e("Music", list[i].getName());
        }
    }
}

How do I similarly get the .mp3 files from external SD card as well?