表情符号无法在 iOS 推送通知中正确呈现

Question

我有一个 Java Spring Boot Web 服务，我正在尝试向 iOS 设备发送推送通知。

我面临的问题是直接粘贴的表情符号文本，例如

String emoji = "";

或者它的代码，比如

 String emoji = "\uD83D\uDE0A";

它显示为?（问号符号）

我尝试将其作为 UTF_8 字符的字节获取，如下所示：

byte[] emojis = user.getEmoji().getBytes(); //Here user.getEmoji() returns a collection of 2-3 emojis
String emojisAsString = new String(emojis, StandardCharsets.UTF_8);
Integer emojiCodePoint = emojisAsString.codePointAt(emojisAsString.offsetByCodePoints(0,0));
char emojiChars[] = {Character.highSurrogate(emojiCodePoint), Character.lowSurrogate(emojiCodePoint)};

但它仍然显示为问号。

我也尝试过使用 UTF-8 代码，"\xE2\x9A\xA1"但这个代码刚刚在通知上打印出来。

此外，当我使用 FCM API 从邮递员那里调用通知 API 并粘贴表情符号时，它会在通知中显示表情符号，当通过 Java Web 服务完成时，它仅显示为问号。

这是推送通知服务代码

 @RequestMapping(value = "/send", method = RequestMethod.GET, produces = "application/json")
    public static ResponseEntity<String> send(String message, String deviceToken, Integer type, Object response, String userNameAsTitle) {

        //response.setMessage(message);
        //response.setNotificationType(type);

        JSONObject body = new JSONObject();
        body.put("to", deviceToken);
        body.put("priority", "high");

        Map<String, Object> map = new HashMap<>();
        map.put("title", userNameAsTitle);
        map.put("body", message);
        //map.put("alert", descprtion);
        map.put("type", type);
        map.put("badge", 1);

        map.put("sound", "default");
        map.put("response", response);

        JSONObject notification = new JSONObject(map);
        //body.put("notification", notification);
        body.put("notification", notification);

        HttpEntity<String> request = new HttpEntity<>(body.toString());

        CompletableFuture<String> pushNotification = androidPushNotificationsService.send(request);
        CompletableFuture.allOf(pushNotification).join();
        try {
            String firebaseResponse = pushNotification.get();
            System.out.println(firebaseResponse.toString());
            return new ResponseEntity<>(firebaseResponse.toString(), HttpStatus.OK);
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }
        return new ResponseEntity<>("Push Notification ERROR!", HttpStatus.BAD_REQUEST);
    }