//创建一个类，此类有两个方法

using Newtonsoft.Json;

namespace System
{
    public static class JsonExtension
    {
        /// <summary>
        /// 把对象转换为JSON字符串
        /// </summary>
        /// <param name="o">对象</param>
        /// <returns>JSON字符串</returns>
        public static string ToJSON(this object o)
        {
            if (o == null)
            {
                return null;
            }
            return JsonConvert.SerializeObject(o);
        }
        /// <summary>
        /// 把Json文本转为实体
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="input"></param>
        /// <returns></returns>
        public static T FromJSON<T>(this string input)
        {
            try
            {
                return JsonConvert.DeserializeObject<T>(input);
            }
            catch (Exception ex)
            {
                return default(T);
            }
        }
    }
}

//使用

User user = new User();
user.UserName = "tom";
user.Age = 22;
user.Sex = 1;
user.Like = "PLAY";

var json= JsonExtension.ToJSON(user);//对象转为Json

string user = "{\"UserName\":\"tom\",\"Age\":22,\"Sex\":1,\"Like\":\"PLAY\"}";//这里使用转义符
var entity = user.FromJSON<User>();//Json转为实体对象