Android get Directory content from web server

Actually I'm developing an app for android.

The app should display all images from a specific directory stored in a webspace.

Example

Host: www.example.org

Folder: /images

Foldercontent

/images/file.png

/images/file2.png

/images/folder/file3.png

I already found out how to display a single image provided by a URL (used the Picasso library)

ImageView appImage = new ImageView(getActivity());

Picasso.with(getActivity()).load("http://www.example.org/images/file.png").into(appImage);

Now my question is, how can I display all images located in a directory and all subfolders?

I have implemented a PHP Script on the Server which provides my the name of all files located in the directory as a text form, but how do I get those names in Android?
How can I call the PHP Script and store the output in a String Array for example?

Or is there a better solution for this, without a PHP Script?

Regards