Serve the Photo

A page shows a product's photo with a tag like <img src="/products/1/photo">. The browser sends a GET to that address and draws whatever image comes back. So the shop answers the photo's bytes as they are, not JSON.

Bytes don't say what they are. The answer's Content-Type header tells the browser how to read them: image/png, image/jpeg... When you return a Map, Spring sets it to application/json for you; for bytes, you set it yourself. A ResponseEntity carries a status, headers and a body. For example, a route that answers plain text:

@GetMapping("/robots.txt")
Object robots() {
    return ResponseEntity.ok().header("Content-Type", "text/plain").body("User-agent: *");
}

URLConnection.guessContentTypeFromName knows the type of each file extension: URLConnection.guessContentTypeFromName("logo.gif") gives "image/gif", and an extension it doesn't know gives null.

After the tests upload two photos, the shop must answer:

POST /products/1/photo  (photo: mug.png, 16 bytes)  →  201  {"filename": "mug.png", "product_id": 1, "size": 16}
POST /products/3/photo  (photo: lamp.jpg, 17 bytes)  →  201  {"filename": "lamp.jpg", "product_id": 3, "size": 17}
GET /products/1/photo  →  200  Content-Type: image/png, the 16 bytes
GET /products/3/photo  →  200  Content-Type: image/jpeg, the 17 bytes
GET /products/2/photo  →  404  {"error": "This product has no photo"}

Your task: add GET /products/{productId}/photo. Look up the product's row in photos; with no row, answer 404; otherwise answer the stored bytes with status 200 and the Content-Type for the photo's file name.

Assignment
Follow the Coding Tutorial to add the method that serves a product's photo.

Hint
java.net.URLConnection is already imported. row.get("filename") is an Object, so cast it with (String). Build the answer with ResponseEntity.ok(), then .header(...), then .body(...).