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Json.NET动态决定属性是否序列化

作者：发布日期：2013-09-05 19:28:19

Tag标签：Json.NET 序列化

昨天提到Json.NET属性序列化设定，接获读者森哥留言:

请问黑大，
针对不需要序列化的「属性」是否可以透过程序「动态」设定或是过滤?

有预感迟早也会遇到这个靠杯火杯的考验，决定打铁趁热，马上来练习。所幸，Json.NET真的很强大，早就料想到此一需求，提供ContractResolver以实现神乎奇技的高度动态化。

我写了一个范例，展示两种动态决定应序列化属性的情境:

Serialize时传入属性名称数组作为参数，正向表列JSON应包含的属性。
由对象属性值决定属性是否要序列化，例如: 如果是女生就不包含年龄。(这几乎已弹性到极点，虽然实务上不常用到)
程序的做法是宣告两个继承自DefaultContractResolver的类别: LimitPropsContractResolver在建构时传入string[]参数列出要序列化的属性名称，并覆写CreateProperties方法，过滤base.CreateProperties()传回的IList<JsonProperty>，只保留前述string[]有列出的属性；HideAgeContractResolver则覆写CreateProperty()方法，由base.CreateProperty()取得JsonProperty，JsonProperty有个ShouldSerialize属性可以传入Lambda表达式，逐笔处理每个要序列化的对象，在Lambda表达式中可将对象转型为原型别进行判断，若不要序列化就传回false。

using System; using System.Collections.Generic; using System.Linq; using System.Reflection; using System.Text; using Newtonsoft.Json; using Newtonsoft.Json.Converters; using Newtonsoft.Json.Serialization; namespace ConsoleApplication1 { class Program { public enum Gender { Male, Female } public class Person { public string Name { get; set; } [JsonConverter(typeof(StringEnumConverter))] public Gender Gender { get; set; } public int Age { get; set; } public Person(string name, Gender gender, int age) { Name = name; Gender = gender; Age = age; } } public class HideAgeContractResolver : DefaultContractResolver { //REF: ?topic=html/ContractResolver.htm protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization) { JsonProperty p = base.CreateProperty(member, memberSerialization); if (p.PropertyName == "Age") { //依性别决定是否要序列化 p.ShouldSerialize = instance => { Person person = (Person)instance; return person.Gender == Gender.Male; }; } return p; } } public class LimitPropsContractResolver : DefaultContractResolver { string[] props = null; public LimitPropsContractResolver(string[] props) { //指定要序列化属性的清单 this.props = props; } //REF: protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization) { IList<JsonProperty> list = base.CreateProperties(type, memberSerialization); //只保留清单有列出的属性 return list.Where(p => props.Contains(p.PropertyName)).ToList(); } } static void Main(string[] args) { List<Person> list = new List<Person>(); list.Add(new Person("George", Gender.Male, 18)); list.Add(new Person("Mary", Gender.Female, 40)); //正常输出 Console.WriteLine(JsonConvert.SerializeObject( list, Formatting.Indented)); var settings = new JsonSerializerSettings(); //加上ContractResolver，正向表列哪些属性要序列化 settings.ContractResolver = new LimitPropsContractResolver("Name,Age".Split(',')); Console.WriteLine(JsonConvert.SerializeObject( list, Formatting.Indented, settings)); //加上ContractResolver，依对象的属性值动态决定要不要序列化 settings.ContractResolver = new HideAgeContractResolver(); Console.WriteLine(JsonConvert.SerializeObject( list, Formatting.Indented, settings)); Console.ReadLine(); } } }

程序执行结果如下，共有三段输出，第一段为正常版；第二段套用LimitPropsContractResolver("Name,Age".Split(','))，故JSON中只见Name及Age，Gender被隐藏；第三段套用了HideAgeContractResolver()，如结果所示，Mary的JSON内容不包含年龄，George则包含。

[ { "Name": "George", "Gender": "Male", "Age": 18 }, { "Name": "Mary", "Gender": "Female", "Age": 40 } ] [ { "Name": "George", "Age": 18 }, { "Name": "Mary", "Age": 40 } ] [ { "Name": "George", "Gender": "Male", "Age": 18 }, { "Name": "Mary", "Gender": "Female" } ]

演练完毕，内心激动澎湃，对Json.NET的景仰如淊淊江水，绵绵不绝~

如果奥斯卡有最佳组件奖，我提名它!