Code
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;
using System.IO;
using System.Runtime.Serialization.Json;
using System.Web.Script.Serialization;

namespace DotNet.Common.Util
{
    /// <summary>
    /// Json操作帮助类
    /// </summary>
    public static class JsonHelper
    {
        #region DataContractJsonSerializer

/// <summary>
        /// 对象转换成json
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="jsonObject">需要格式化的对象</param>
        /// <returns>Json字符串</returns>
        public static string DataContractJsonSerialize<T>(T jsonObject)
        {
            DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(T));
            string json = null;
            using (MemoryStream ms = new MemoryStream()) //定义一个stream用来存发序列化之后的内容
            {
                serializer.WriteObject(ms, jsonObject);
                json = Encoding.UTF8.GetString(ms.GetBuffer()); //将stream读取成一个字符串形式的数据，并且返回
                ms.Close();
            }
            return json;
        }

/// <summary>
        /// json字符串转换成对象
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="json">要转换成对象的json字符串</param>
        /// <returns></returns>
        public static T DataContractJsonDeserialize<T>(string json)
        {
            DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(T));
            T obj = default(T);
            using (MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(json)))
            {
                obj = (T)serializer.ReadObject(ms);
                ms.Close();
            }
            return obj;
        }

#endregion

#region JavaScriptSerializer  ms这里的两个方法已经out了

//“System.Web.Script.Serialization.JavaScriptSerializer.JavaScriptSerializer()”已过时: 
        //“The recommended alternative is System.Runtime.Serialization.DataContractJsonSerializer.”

/// <summary>
        /// 对象转换成json
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="jsonObject"></param>
        /// <returns></returns>
        public static string JavaScriptSerialize<T>(T jsonObject)
        {
            JavaScriptSerializer serializer = new JavaScriptSerializer();
            StringBuilder sb = new StringBuilder();
            serializer.Serialize(jsonObject, sb);
            return sb.ToString();
        }

/// <summary>
        /// json字符串转换成对象
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="json"></param>
        /// <returns></returns>
        public static T JavaScriptDeserialize<T>(string json)
        {
            var result = new JavaScriptSerializer().Deserialize<T>(json);
            return (T)result;
        }

#endregion
    }
}

Code
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Text;

namespace WebTest
{
    using DotNet.Common.WebForm;
    using DotNet.Common.Model;
    using EntCor.Hrm.Model;
    using DotNet.Common.Util;

public partial class JsonTest : BasePage
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                Company company = new Company { ID = 123456789, CompanyName = "test" };
                List<Employee> listEmployees = new List<Employee>();
                Employee employee = new Employee { ID = 1, UserName = "jeff wong", Password = "123456", Address = "北京", Birthday = DateTime.Now.AddYears(-25), IsLeave = false, RealName = "测试用户", State = "2" };
                listEmployees.Add(employee);
                employee = new Employee { ID = 2, UserName = "jeffery zhao", Password = "654321", Address = "上海", Birthday = DateTime.Now.AddYears(-25), IsLeave = false, RealName = "测试用户2", State = "2" };
                listEmployees.Add(employee);
                company.Employees = listEmployees;
                //对象序列化为json
                string jsonStr = DotNet.Common.Util.JsonHelper.DataContractJsonSerialize<Company>(company);//等价于过时的 string jsonStr = DotNet.Common.Util.JsonHelper.JavaScriptSerialize<Company>(company);
                this.ltrContext.Text = jsonStr;

//json字符串反序列化为对象
                Company jsonCompany = DotNet.Common.Util.JsonHelper.DataContractJsonDeserialize<Company>(jsonStr);
                Company jsonJsCompany = DotNet.Common.Util.JsonHelper.JavaScriptDeserialize<Company>(jsonStr); //过时了
                Response.Write("公司id:"+jsonCompany.ID);
                Response.Write("<br/><br/>公司id:" + jsonJsCompany.ID);
            }
        }
    }
}