如何从用户请求中获取用户代理？

Question

I have to get User-agent from a user request and add custom info to that User-agent and send it back. I have the following controller:

@RequestMapping("/orders")
@Controller
public class MyController {
    @GetMapping("/new_order")
    public String newOrder(RedirectAttributes redirectAttributes, Model model) {
        if (isUserNotAuthorized()) {
            return getLoginRedirectPage(redirectAttributes, "/login");
        }
        model.addAttribute("order", new Order());
        // How to retrieve User-agent and add some custom info and return it back to the user?
        return "new_order";
    }
}

Thanks for your help!

Answer 1

You can get the header from the request in the following way

    @GetMapping("/new_order")
    public String newOrder(@RequestHeader(value = "User-Agent") String userAgent, RedirectAttributes redirectAttributes, Model model) {
           //...
    }

To send the headers back to the client, you can use ResponseEntity

public ResponseEntity<String> newOrder() {
    HttpHeaders responseHeaders = new HttpHeaders();
    responseHeaders.set("User-Agent", "updated-Value");

    return ResponseEntity.ok()
      .headers(responseHeaders)
      .body("New order created.");
}

Answer 2

Inject HttpServletRequest in your controller method. From there use HttpServletRequest#getHeader(...) to get the header you need.

    @GetMapping("/new_order")
    public String newOrder(RedirectAttributes redirectAttributes, HttpServletRequest request, Model model) {
        String userAgent = request.getHeader("User-Agent");
        if (isUserNotAuthorized()) {
            return getLoginRedirectPage(redirectAttributes, "/login");
        }
        model.addAttribute("order", new Order());
        // How to retrieve User-agent and add some custom info and return it back to the user?
        return "new_order";
    }