Follow the Pages in Java

A long list is rarely sent in one answer. APIs split it into pages: each answer holds a few items and says which page comes next. You keep asking until there is no next page.

You don't know in advance how many pages there are, so use a while loop that stops when the next page is null (JSON's null becomes Java's null, so keep the page number in an Integer, which can be null, not an int). Here is the same idea on a plain map, following a chain of bus stops:

Map<String, String> nextStop = new HashMap<>();
nextStop.put("Home", "Park");
nextStop.put("Park", "School");
nextStop.put("School", null);
String stop = "Home";
while (stop != null) {
    System.out.println(stop);
    stop = nextStop.get(stop);
}

The supplier's /catalog has 5 products, 2 per page:

GET /catalog?page=1  →  {"page": 1, "items": ["Mug", "Notebook"], "next_page": 2}
GET /catalog?page=2  →  {"page": 2, "items": ["Lamp", "Pen"], "next_page": 3}
GET /catalog?page=3  →  {"page": 3, "items": ["Plant"], "next_page": null}

Your program must print:

Page 1
Mug
Notebook
Page 2
Lamp
Pen
Page 3
Plant

Your task: start at page 1 and keep asking /catalog for the page that next_page names, until it is null. For each page, print Page and its number, then every product name on it.

Assignment
Follow the Coding Tutorial to read every page of the catalog and print all its products.

Hint
Build the URL with SUPPLIER + "/catalog?page=" + page. Set page to (Integer) data.get("next_page") as the last line of the loop, or the program will ask for page 1 forever.