ajax提交参数到后台无法映射

前端代码

$('button').click(function(){
    var topic={};
    topic.tTitle='biaoti';
    topic.tContents='nihao';
    topic.tSid=1;
    var tags="lombok";
    $.post("http://127.0.0.1:8080/topic",{"topic":topic,"tags":tags},function(resp){
        console.log(resp);
    })
})

后端代码

public String insertTopic(Topic topic, String tags){
    System.out.println(tags +"---"+ topic);
    return "success";
}

实体类

@Data
public class Topic{

  private long tId;
  private long tUid;
  private long tSid;
  private String tTitle;
  private String tContents;
  private String tTime;
  private long tState;
  private String tLabel;
  private String tType;
  private long tVisited;
  private long tLike;
  private long tDislike;
  private long tCollection;
  private long tComment;
  private long tForward;
}

前端ajax提交后后端接收情况

lombok---Topic(tId=0, tUid=0, tSid=0, tTitle=null, tContents=null, tTime=null, tState=0, tLabel=null, tType=null, tVisited=0, tLike=0, tDislike=0, tCollection=0, tComment=0, tForward=0)

topic对象接收一直为空，但是我在swagger中进行提交就可以全部接收到

topic.tags = tags ;

$.post("http://127.0.0.1:8080/topic",topic,function(resp){
console.log(resp);
})