目次

C#でJSONを読み書きしてみる

2016/12/11
自分用メモ

下準備

参照にアセンブリ System.Runtime.Serialization を追加しておく。

クラスをJSONでシリアライズする

C#の属性でシリアライズするクラスやメンバーを明示する。“[DataContract]“や”[EnumMember]”、”[DataMember]”がそれ。 

using System;
using System.IO;
using System.Text;
using System.Collections;
using System.Runtime.Serialization.Json;
using System.Runtime.Serialization;
 
namespace jsonparse
{
    [DataContract]
    public enum jsonenum
    {
        [EnumMember] key1,
        [EnumMember] key2,
        [EnumMember] key3
    };
    [DataContract]
    public class jsonObject
    {
        [DataMember] public bool keyBool = true;
        [DataMember] public int keyInt = 360;
        [DataMember] public double keyDouble = 3.141592653;
        [DataMember] public string keyString = "this is json";
        [DataMember] public jsonenum keyEnum = jsonenum.key2;
        [DataMember] public int[] keyArraryInt = new int[] { 10, 100, 100 };
        [DataMember] public ArrayList keyArrayList = new ArrayList() { 1980, "abcd" };
        [DataMember] public Hashtable keyHashtable = new Hashtable() { { "key100", 100 }, { "key200", 200 } };
    }
    class Program
    {
        static void Main(string[] args)
        {
            jsonObject json = new jsonObject();
 
            DataContractJsonSerializer js = new DataContractJsonSerializer(typeof(jsonObject));
            MemoryStream ms = new MemoryStream();
            js.WriteObject(ms, json);
 
            Encoding e = Encoding.UTF8;
 
            Console.WriteLine(e.GetString(ms.GetBuffer()));
        }
    }
}

コンパイルして jsonparse.exe を作ったので実行してみる。 

E:\work>jsonparse.exe
{"keyArraryInt":[10,100,100],"keyArrayList":[1980,"abcd"],"keyBool":true,"keyDouble":3.141592653,"keyEnum":1,"keyHashtable":[{"Key":"key100","Value":100},{"Key":"key200","Value":200}],"keyInt":360,"keyString":"this is json"}
 
E:\work>

出力されたJSONを JSON Pretty Linter - JSONの整形と構文チェック で整形するとこうなる。

出力されたJSON 対応するjsonObjectのメンバ 
{
    "keyArraryInt": [
        10,
        100,
        100
    ],
    "keyArrayList": [
        1980,
        "abcd"
    ],
    "keyBool": true,
    "keyDouble": 3.141592653,
    "keyEnum": 1,
    "keyHashtable": [
        {
            "Key": "key100",
            "Value": 100
        },
        {
            "Key": "key200",
            "Value": 200
        }
    ],
    "keyInt": 360,
    "keyString": "this is json"
}
[DataMember] public int[] keyArraryInt = new int[] { 10, 100, 100 };
[DataMember] public ArrayList keyArrayList = new ArrayList() { 1980, "abcd" };
[DataMember] public bool keyBool = true;
[DataMember] public double keyDouble = 3.141592653;
[DataMember] public jsonenum keyEnum = jsonenum.key2;
[DataMember] public Hashtable keyHashtable = new Hashtable() { { "key100", 100 }, { "key200", 200 } };
[DataMember] public int keyInt = 360;
[DataMember] public string keyString = "this is json";

enum は JavaScript に無いので名称ではなく値で表現される。 値をしてしていない jsonenum はkey1～key3のメンバーに0～2が割り当てされている。 配列やリストは、要素の並びが正しく反映されている。

デシリアライズでJSONの内容をクラスに反映させる

入力サンプルのJSONコードを用意する。

sample.json
{
    "keyArraryInt": [
        5000,
        200,
        300
    ],
    "keyArrayList": [
        "ABCD",
        2016
    ],
    "keyBool": false,
    "keyDouble": 1.41421356,
    "keyEnum": 0,
    "keyHashtable": [
        {
            "Key": "key300",
            "Value": 300
        },
        {
            "Key": "key500",
            "Value": 500
        },
        {
            "Key": "key800",
            "Value": 800
        }
    ],
    "keyInt": 180,
    "keyString": "これはJSONですね"
}

先のプログラムを書き換えてコンパイル、実行してみる。 

using System;
using System.IO;
using System.Collections;
using System.Runtime.Serialization.Json;
using System.Runtime.Serialization;
 
namespace jsonparse
{
    [DataContract]
    public enum jsonenum
    {
        [EnumMember] key1,
        [EnumMember] key2,
        [EnumMember] key3
    };
    [DataContract]
    public class jsonObject
    {
        [DataMember] public bool keyBool = true;
        [DataMember] public int keyInt = 360;
        [DataMember] public double keyDouble = 3.141592653;
        [DataMember] public string keyString = "this is json";
        [DataMember] public jsonenum keyEnum = jsonenum.key2;
        [DataMember] public int[] keyArraryInt = new int[] { 10, 100, 100 };
        [DataMember] public ArrayList keyArrayList = new ArrayList() { 1980, "abcd" };
        [DataMember] public Hashtable keyHashtable = new Hashtable() { { "key100", 100 }, { "key200", 200 } };
    }
    class Program
    {
        static void Main(string[] args)
        {
 
            DataContractJsonSerializer js = new DataContractJsonSerializer(typeof(jsonObject));
            FileStream fs = new FileStream("sample.json", FileMode.Open);
            jsonObject json = (jsonObject)js.ReadObject(fs);
            fs.Close();
 
            Console.WriteLine("keyBool      = {0}", json.keyBool);
            Console.WriteLine("keyInt       = {0}", json.keyInt);
            Console.WriteLine("keyDouble    = {0}", json.keyDouble);
            Console.WriteLine("keyString    = {0}", json.keyString);
            Console.WriteLine("keyEnum      = {0}", json.keyEnum);
            Console.WriteLine("keyArrayInt  = {0}", String.Join(", ", json.keyArraryInt));
            Console.WriteLine("keyArrayList = {0}", String.Join(", ", json.keyArrayList.ToArray()));
 
            ArrayList sa = new ArrayList();
            foreach(DictionaryEntry x in json.keyHashtable)
            {
                sa.Add(x.Key.ToString() + "->"  + x.Value.ToString());
            }
            Console.WriteLine("keyHashtable = {0}", String.Join(", ", sa.ToArray()));
 
        }
    }
}

実行結果から、クラス jsonObject の初期値がJSONドキュメントで更新されていることが分かる。 

C:\work>jsonparse.exe
keyBool      = False
keyInt       = 180
keyDouble    = 1.41421356
keyString    = これはJSONですね
keyEnum      = key1
keyArrayInt  = 5000, 200, 300
keyArrayList = ABCD, 2016
keyHashtable = key800->800, key500->500, key300->300
 
C:\work>

JSONからNULLを入力してみる

もし入力にNULLが含まれる場合、デシリアライズするクラスはNULL許容するメンバで構成されている必要がある。 

using System;
using System.IO;
using System.Runtime.Serialization.Json;
using System.Runtime.Serialization;
 
namespace jsonparse
{
    [DataContract]
    public enum jsonenum
    {
        [EnumMember] key1,
        [EnumMember] key2,
        [EnumMember] key3
    };
    [DataContract]
    public class jsonObject
    {
        [DataMember] public bool? keyBool = true;
        [DataMember] public int? keyInt = 360;
        [DataMember] public double? keyDouble = 3.141592653;
        [DataMember] public string keyString = "this is json";
        [DataMember] public jsonenum? keyEnum = jsonenum.key2;
    }
    class Program
    {
        static void Main(string[] args)
        {
            DataContractJsonSerializer js = new DataContractJsonSerializer(typeof(jsonObject));
            FileStream fs = new FileStream("sample.json", FileMode.Open);
            jsonObject json = (jsonObject)js.ReadObject(fs);
            fs.Close();
 
            Console.WriteLine("keyBool      = {0}", json.keyBool );
            Console.WriteLine("keyInt       = {0}", json.keyInt );
            Console.WriteLine("keyDouble    = {0}", json.keyDouble );
            Console.WriteLine("keyString    = {0}", json.keyString );
            Console.WriteLine("keyEnum      = {0}", json.keyEnum );
        }
    }
}

bool,int,double,enum で ”?”を付与しているのはNULL許容型の宣言。stringは元々NULLを許容している。 結果は以下の通り。

JSON入力 結果 
{
    "keyBool": null,
    "keyInt": null,
    "keyDouble": null,
    "keyString": null,
    "keyEnum": null
}
C:\work>jsonparse.exe
keyBool      =
keyInt       =
keyDouble    =
keyString    =
keyEnum      =
 
C:\work>
 
{
    "keyBool": false,
    "keyInt": 270,
    "keyDouble": 2.77,
    "keyString": "This is a pen.",
    "keyEnum": 2
}
C:\work>jsonparse.exe
keyBool      = False
keyInt       = 270
keyDouble    = 2.77
keyString    = This is a pen.
keyEnum      = key3
 
C:\work>
, ,