import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class ConcurrentDateUtil {
  private static ThreadLocal threadLocal = new ThreadLocal() {
    @Override
    protected DateFormat initialValue() {
      return new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
    }
  };

  public static Date parse(String dateStr) throws ParseException {
    return threadLocal.get().parse(dateStr);
  }

  public static String format(Date date) {
    return threadLocal.get().format(date);
  }
}

import com.sf.utils.ConcurrentDateUtil;

import java.util.Date;

public class JsonResult {
  public static int NEED_RE_LOGIN = 1;
  public static int NEED_RETRY = 2;

  private int errCode;

  private String message;

  private String timestamp = ConcurrentDateUtil.format(new Date());

  private T data;

  public String getMessage() {
    return message;
  }

  public void setMessage(String message) {
    this.message = message;
  }

  public String getTimestamp() {
    return timestamp;
  }

  public T getData() {
    return data;
  }

  public void setData(T data) {
    this.data = data;
  }

  public int getErrCode() {
    return errCode;
  }

  public void setErrCode(int errCode) {
    this.errCode = errCode;
  }
}

@ResponseBody
@RequestMapping(value = "/user/getUserAmount", method = RequestMethod.POST)
public JsonResult> getUserAmount() {
  JsonResult> result = new JsonResult<>();
  try {
    //已签到人数
    Integer signedAmount = userService.getSignedAmount();
    //总人数
    Integer totalUserAmount = userService.getTotalUserAmount();
    Map amountMap = new HashMap<>();
    amountMap.put("signed", signedAmount);
    amountMap.put("sum", totalUserAmount);
    result.setData(amountMap);
    //这里举个例子，如果觉得setData穿的信息不够，还可以用setMessage方法多传一个字符串过去
    result.setMessage("这是签到界面");
  } catch (Exception e) {
    log.warn(ExceptionUtils.getStackTrace(e));
  }
  return result;
}

function getSignedAmount(){
  $.ajax({
    type: "post",
    url : getContextPath() + "/user/getUserAmount",
    dataType:'json',
    data: {
    },
    success: function(data){
      var amount = data.data;
      //取出总人数
      var totalAmount = amount.sum;
      //总人数减去已经签到的人数，就是未签到的人
      var unsignedNumber = amount.sum-amount.signed;
      //取出后端controller中setMessage方法传过来的字符串
      var logMessage = data.message;
    }
  });
}