javascript 保存cookie 有时候不成功 怎么回事儿，有

function addCookie(name,value)
{
    var Days = 30;
    var exp  = new Date();
    exp.setTime(exp.getTime() + Days*24*60*60*1000);
//  alert(value);
  document.cookie = name + "="+ escape(value) + ";expires=" + exp.toGMTString();
};

有时候能保存，有时候保存不了，怎么回事?

---

        List columns = CurrentTcaManagementPage_grid.getColumns().getChildren();

        SimpleModelComp alarmStateAsc = new SimpleModelComp(ThresholdCrossingAlarm.class, "tcaAlarmState", true);
        SimpleModelComp alarmStateDesc = new SimpleModelComp(ThresholdCrossingAlarm.class, "tcaAlarmState", false);
        ((Column) columns.get(0)).setSortAscending(alarmStateAsc);
        ((Column) columns.get(0)).setSortDescending(alarmStateDesc);

---

import java.lang.reflect.Field;
import java.util.Comparator;
import java.util.Date;

public class SimpleModelComp implements Comparator
{
    private Class sortClass;

    private Field sortField = null;

    private boolean asc;

    public SimpleModelComp(Class dataType, String fieldName, boolean isAsc)
    {