SpringMVC @RequestBody 为null问题的排查及解决

@PostMapping("/update")
@ApiOperation("更新用户信息")
public CumResponseBody update(@RequestBody UserInfoParam param) {
     int userId = getUserId();
     userService.updateUserInfo(userId, param);
     return ResponseFactory.createSuccessResponse("ok");
}
//UserInfoParam.java
public class UserInfoParam {
    private String tel;
    private String email;
    public String getTel() {
        return tel;
    }
    public void setTel(String tel) {
        this.tel = tel;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
}

curl -X POST --header 'Content-Type: application/json' --header 'Accept: application/json' -d '{ \ 
   "email": "12%40mail.com", \ 
   "tel": "13677682911" \ 
 }' 'http://127.0.0.1:9998/api/user/update'

public boolean markSupported() {
    return false;
}
public synchronized void reset() throws IOException {
        throw new IOException("mark/reset not supported");
}
public synchronized void mark(int readlimit) {}

    public synchronized void mark(int readlimit) {
        marklimit = readlimit;
        markpos = pos;
    }
    public synchronized void reset() throws IOException {
        getBufIfOpen(); // Cause exception if closed
        if (markpos < 0)
            throw new IOException("Resetting to invalid mark");
        pos = markpos;
    }
    public boolean markSupported() {
        return true;
    }

protected <T> Object readWithMessageConverters(HttpInputMessage inputMessage, MethodParameter parameter,
            Type targetType) throws IOException, HttpMediaTypeNotSupportedException, HttpMessageNotReadableException {
        MediaType contentType;
        boolean noContentType = false;
        try {
            contentType = inputMessage.getHeaders().getContentType();
        }
        catch (InvalidMediaTypeException ex) {
            throw new HttpMediaTypeNotSupportedException(ex.getMessage());
        }
        if (contentType == null) {
            noContentType = true;
            contentType = MediaType.APPLICATION_OCTET_STREAM;
        }
        Class<?> contextClass = parameter.getContainingClass();
        Class<T> targetClass = (targetType instanceof Class ? (Class<T>) targetType : null);
        if (targetClass == null) {
            ResolvableType resolvableType = ResolvableType.forMethodParameter(parameter);
            targetClass = (Class<T>) resolvableType.resolve();
        }
        HttpMethod httpMethod = (inputMessage instanceof HttpRequest ? ((HttpRequest) inputMessage).getMethod() : null);
        Object body = NO_VALUE;
        EmptyBodyCheckingHttpInputMessage message;
        try {
            message = new EmptyBodyCheckingHttpInputMessage(inputMessage);
            for (HttpMessageConverter<?> converter : this.messageConverters) {
                Class<HttpMessageConverter<?>> converterType = (Class<HttpMessageConverter<?>>) converter.getClass();
                GenericHttpMessageConverter<?> genericConverter =
                        (converter instanceof GenericHttpMessageConverter ? (GenericHttpMessageConverter<?>) converter : null);
                if (genericConverter != null ? genericConverter.canRead(targetType, contextClass, contentType) :
                        (targetClass != null && converter.canRead(targetClass, contentType))) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Read [" + targetType + "] as \"" + contentType + "\" with [" + converter + "]");
                    }
                    if (message.hasBody()) {
                        HttpInputMessage msgToUse =
                                getAdvice().beforeBodyRead(message, parameter, targetType, converterType);
                        body = (genericConverter != null ? genericConverter.read(targetType, contextClass, msgToUse) :
                                ((HttpMessageConverter<T>) converter).read(targetClass, msgToUse));
                        body = getAdvice().afterBodyRead(body, msgToUse, parameter, targetType, converterType);
                    }
                    else {
                        body = getAdvice().handleEmptyBody(null, message, parameter, targetType, converterType);
                    }
                    break;
                }
            }
        }
        catch (IOException ex) {
            throw new HttpMessageNotReadableException("I/O error while reading input message", ex);
        }
        if (body == NO_VALUE) {
            if (httpMethod == null || !SUPPORTED_METHODS.contains(httpMethod) ||
                    (noContentType && !message.hasBody())) {
                return null;
            }
            throw new HttpMediaTypeNotSupportedException(contentType, this.allSupportedMediaTypes);
        }
        return body;
    }

$.ajax({　　　　　　　
        　url:"/login",　　　　　　　
        　type:"POST",　　　　　　　　
          data:'{"userName":"admin","pwd","admin123"}',　　　　　　
      　　content-type:"application/json charset=utf-8",　　　　　　　　
          success:function(data)
             {　　　　　　　　　　
                alert("request success ! ");　　　　　　　
           　}　　　　
});

@requestMapping("/login")　　　　
  public void login(@requestBody String userName,@requestBody String pwd){　　　　　　
  System.out.println(userName+" ："+pwd);　　　　
}

String userName;
String pwd;