import org.springframework.core.io.Resource;
import org.springframework.core.io.UrlResource;
import org.springframework.http.HttpHeaders;
import org.springframework.http.ResponseEntity;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import java.net.MalformedURLException;
import java.nio.file.Path;
import java.nio.file.Paths;

@Controller
public class HtmlController {

    @GetMapping("/custom-page")
    public ResponseEntity<Resource> serveHtml() {
        try {
            Path file = Paths.get("path/to/your/file.html");
            Resource resource = new UrlResource(file.toUri());

            if (resource.exists() || resource.isReadable()) {
                return ResponseEntity.ok()
                        .header(HttpHeaders.CONTENT_TYPE, "text/html")
                        .body(resource);
            } else {
                return ResponseEntity.notFound().build();
            }
        } catch (MalformedURLException e) {
            return ResponseEntity.badRequest().build();
        }
    }
}