我研究了使用@JsonSerialize（作为=字符串.类，使用= SomeSerializer.类）
其中一个选项是通过扩展JsonSerializer并重写其serialize()方法来创建自定义序列化程序。
serialize()的一个参数是JsonGenerator，顾名思义，它允许生成JSON。您可以在相当低的级别上使用JsonGenerator，通过手动指定JSON对象（JSON数组）的开始/结束，写入字段名等，或者您可以将嵌套对象原样馈送到JsonGenerator中，这取决于它的默认形状是否满足您的需要。
这就是它看起来的样子（* 我没有在JSON中使用“GCM”和“ADM”属性，因为不清楚它们应该来自哪里 *）。

@JsonSerialize(using = SNSNotificationSerializer.class)
record SNSNotification(
    @JsonProperty("default") String defaultMessage,
    @JsonProperty("APNS") APNS apns
) {}

public class SNSNotificationSerializer extends JsonSerializer<SNSNotification> {
    @Override
    public void serialize(SNSNotification value,
                          JsonGenerator gen,
                          SerializerProvider serializers) throws IOException {
        
        gen.writeStartObject();     // {
        gen.writeStringField("default", value.defaultMessage()); // "default": " ",
        gen.writeFieldName("APNS"); // "APNS" :
        gen.writeStartObject();     // {
        gen.writeFieldName("aps");  // "aps" :
        gen.writeStartObject();     // {
        gen.writeStringField("alert", value.apns().aps().alert()); // "alert" : " ",
        gen.writeStringField("url", "www.amazon.com");             // "url":"www.amazon.com"
        gen.writeEndObject();       // }
        gen.writeEndObject();       // }
        gen.writeEndObject();       // }
    }
}

• 用法示例：*

SNSNotification snsNotification = new SNSNotification(
    "This is the default message which must be present when publishing a message to a topic. The default message will only be used if a message is not present for one of the notification platforms.",
    new APNS(new APS("Check out these awesome deals!"))
);
        
ObjectMapper mapper = new ObjectMapper();
        
String json = mapper
    .writerWithDefaultPrettyPrinter()
    .writeValueAsString(snsNotification);
    
System.out.println(json);

• 输出：*

{
  "default" : "This is the default message which must be present when publishing a message to a topic. The default message will only be used if a message is not present for one of the notification platforms.",
  "APNS" : {
    "aps" : {
      "alert" : "Check out these awesome deals!",
      "url" : "www.amazon.com"
    }
  }
}