datetime-local获取的值为null，急急急！

大牛们，我昨晚已经在提问区提问了。。。但是没解决，白天再来问一下，就是我前端用的datetime-local来设置时间，但是在后台获取的时候，却为null，时间属性我也有加上注解，通过对象中其他属性都能正常获取，请问该怎么解决？
####前端

    <div class="form-group">    
                <label class="col-sm-3 control-label">培训开始时间：</label>
                <div class="col-sm-8">
                    <input id="trainStarttime" name="trainStarttime" th:field="*{trainStarttime}" class="form-control" type="datetime-local" required>
                </div>
            </div>
            <div class="form-group">    
                <label class="col-sm-3 control-label">培训结束时间：</label>
                <div class="col-sm-8">
                    <input id="trainEndtime" name="trainEndtime"  th:field="*{trainEndtime}" class="form-control" type="datetime-local"  required>
                </div>
            </div>

####bean类

@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")
private Date trainStarttime;


@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")
private Date trainEndtime;

对应的getter和setter方法

public String getTrainPlace()
        {
        return trainPlace;
        }
public void setTrainStarttime(Date trainStarttime)
        {
        this.trainStarttime = trainStarttime;
        }

public Date getTrainStarttime()
        {
        return trainStarttime;
        }
public void setTrainEndtime(Date trainEndtime)
        {
        this.trainEndtime = trainEndtime;
        }

public Date getTrainEndtime()
        {
        return trainEndtime;
        }

####后台

        @PostMapping("/add")
    @ResponseBody
    public AjaxResult addSave(TrainApplication trainApplication)
    {
        System.out.println("!@#"+trainApplication);
        return toAjax(trainApplicationService.insertTrainApplication(trainApplication));
    }           

            获取的内容：

            trainName=123
  trainTarget=312
  trainForm=312
  trainTutor=321
  trainPlace=312
  trainStarttime=<null>
  trainEndtime=<null>

页面表单

<input id="wbTime" name="wbTime" class="form-control" type="datetime-local" >

页面赋值

$(document).ready(function(){
    var t = "${asset.wbTime!,'yyyy-MM-dd HH:mm'}";
    t = t.substring(0,10)+'T'+t.substring(11,16);
    $("#wbTime").val(t);
})

实体类

public Date getWbTime() {
        return wbTime;
    }

    public void setWbTime(Date wbTime) {
        this.wbTime = wbTime;
    }