List of files in assets folder and its subfolders

I have some folders with HTML files in the "assets" folder in my Android project. I need to show these HTML files from assets' sub-folders in a list. I already wrote some code about making this list.

lv1 = (ListView) findViewById(R.id.listView);
// Insert array in ListView

// In the next row I need to insert an array of strings of file names
// so please, tell me, how to get this array

lv1.setAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, filel));
lv1.setTextFilterEnabled(true);
// onclick items in ListView:
lv1.setOnItemClickListener(new OnItemClickListener() {
    public void onItemClick(AdapterView<?> a, View v, int position, long id) {
        //Clicked item position
        String itemname = new Integer(position).toString();  
        Intent intent = new Intent();
        intent.setClass(DrugList.this, Web.class);
        Bundle b = new Bundle();
        //I don't know what it's doing here
        b.putString("defStrID", itemname); 
        intent.putExtras(b);
        //start Intent
        startActivity(intent);
    }
});