here is the successful code. I can"t find a more concise way. It is said that this method is not good for mobile phone support

  const data = new URLSearchParams();
    data.append("beUserId", userId);
    axios.post("/user/attention", data)
        .then(response => {
            console.log(response.data)
    })
                

background JAVA code:

@PostMapping("/attention")
@ResponseBody
public String attention(Integer beUserId) {
    System.out.println(beUserId);
    return "";
}