Newtonsoft Json.NET动态决定属性是否序列化

转自：http://www.it165.net/pro/html/201309/7044.html

本人用了，解决了现实的业务问题。

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。
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sourceprint?

01.

using

System;

02.

using

System.Collections.Generic;

03.

using

System.Linq;

04.

using

System.Reflection;

05.

using

System.Text;

06.

using

Newtonsoft.Json;

07.

using

Newtonsoft.Json.Converters;

08.

using

Newtonsoft.Json.Serialization;

09.

10.

namespace

ConsoleApplication1

11.

{

12.

class

Program

13.

{

14.

public

enum

Gender

15.

{

16.

Male,
 Female

17.

}

18.

19.

public

class

Person

20.

{

21.

public

string

Name
 {

get

;

set

;
 }

22.

[JsonConverter(

typeof

(StringEnumConverter))]

23.

public

Gender
 Gender {

get

;

set

;
 }

24.

public

int

Age
 {

get

;

set

;
 }

25.

public

Person(

string

name,
 Gender gender,

int

age)

26.

{

27.

Name
 = name;Gender = gender;Age = age;

28.

}

29.

}

30.

31.

public

class

HideAgeContractResolver
 :DefaultContractResolver

32.

{

33.

//REF:http://james.newtonking.com/projects/json/help/index.html?topic=html/ContractResolver.htm

34.

protected

override

JsonProperty
 CreateProperty(MemberInfo member,

35.

MemberSerialization
 memberSerialization)

36.

{

37.

JsonProperty
 p =

base

.CreateProperty(member,
 memberSerialization);

38.

if

(p.PropertyName
 ==

"Age"

)

39.

{

40.

//依性别决定是否要序列化

41.

p.ShouldSerialize
 = instance =>

42.

{

43.

Person
 person = (Person)instance;

44.

return

person.Gender
 == Gender.Male;

45.

};

46.

}

47.

return

p;

48.

}

49.

}

50.

51.

public

class

LimitPropsContractResolver
 :DefaultContractResolver

52.

{

53.

string

[]
 props =

null

;

54.

public

LimitPropsContractResolver(

string

[]
 props)

55.

{

56.

//指定要序列化属性的清单

57.

this

.props
 = props;

58.

}

59.

//REF:http://james.newtonking.com/archive/2009/10/23/efficient-json-with-json-net-reducing-serialized-json-size.aspx

60.

protected

override

IList<JsonProperty>
 CreateProperties(Type type,

61.

MemberSerialization
 memberSerialization)

62.

{

63.

IList<JsonProperty>
 list =

64.

base

.CreateProperties(type,
 memberSerialization);

65.

//只保留清单有列出的属性

66.

return

list.Where(p
 =>props.Contains(p.PropertyName)).ToList();

67.

}

68.

69.

}

70.

71.

static

void

Main(

string

[]
 args)

72.

{

73.

List<Person>
 list =

new

List<Person>();

74.

list.Add(

new

Person(

"George"

,
 Gender.Male, 18));

75.

list.Add(

new

Person(

"Mary"

,
 Gender.Female, 40));

76.

//正常输出

77.

Console.WriteLine(JsonConvert.SerializeObject(

78.

list,
 Formatting.Indented));

79.

var
 settings =

new

JsonSerializerSettings();

80.

//加上ContractResolver，正向表列哪些属性要序列化

81.

settings.ContractResolver
 =

82.

new

LimitPropsContractResolver(

"Name,Age"

.Split(

','

));

83.

Console.WriteLine(JsonConvert.SerializeObject(

84.

list,
 Formatting.Indented, settings));

85.

//加上ContractResolver，依对象的属性值动态决定要不要序列化

86.

settings.ContractResolver
 = 

new

HideAgeContractResolver();

87.

Console.WriteLine(JsonConvert.SerializeObject(

88.

list,
 Formatting.Indented, settings));

89.

Console.ReadLine();

90.

91.

}

92.

}

93.

}

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。



view
sourceprint?

01.

[

02.

{

03.

"Name"

:

"George"

,

04.

"Gender"

:

"Male"

,

05.

"Age"

:
 18

06.

},

07.

{

08.

"Name"

:

"Mary"

,

09.

"Gender"

:

"Female"

,

10.

"Age"

:
 40

11.

}

12.

]

13.

[

14.

{

15.

"Name"

:

"George"

,

16.

"Age"

:
 18

17.

},

18.

{

19.

"Name"

:

"Mary"

,

20.

"Age"

:
 40

21.

}

22.

]

23.

[

24.

{

25.

"Name"

:

"George"

,

26.

"Gender"

:

"Male"

,

27.

"Age"

:
 18

28.

},

29.

{

30.

"Name"

:

"Mary"

,

31.

"Gender"

:

"Female"

32.

}

33.

]

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!