[C#.net] 產生JSON字串的幾種方式整理

2012-08-16

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.Net Framework
2014-06-17

↙部落格忽然多了好多回應有關Json的文章，讓我想起我還沒寫怎麼產生JSON字串XD

這邊就以Google API裡有段JSON字串當作練習怎麼產生：

以下整理幾種我見過的方式(個人推薦的放在最後^_^)

1. 字串拼接

最麻煩的方式，可讀性也差，若遇到Boolean型別的變數要記得轉小寫


protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)//Get Method
        {
            //準備資料
            string collapse_key = "score_update";
            int time_to_live = 108;
            bool delay_while_idle = true;
            string score = "4x8";
            string time = "15:16.2342";
            List<string> registration_ids = new List<string>() { "4","8","15","16","23","42"};


            //開始拼接字串
            StringBuilder sb = new StringBuilder();
            sb.AppendLine("{");
            sb.AppendLine("\"collapse_key\":\""+collapse_key+"\",");
            sb.AppendLine("\"time_to_live\":"+time_to_live+",");
            sb.AppendLine("\"delay_while_idle\":"+delay_while_idle.ToString().ToLower()+",");
            sb.AppendLine("\"data\":{");
            sb.AppendLine("\"score\":\""+score+"\",");
            sb.AppendLine("\"time\":\""+time+"\"");
            sb.AppendLine("},");
            sb.AppendLine("\"registration_ids\":[");
            foreach (string item in registration_ids)
            {
                sb.Append("\""+item+"\",");
            }
            sb = new StringBuilder(sb.ToString().TrimEnd(','));//移除最後一個「,」字元
            sb.AppendLine("]");
            sb.AppendLine("}");

            //輸出結果
            Response.Write(sb.ToString());
        }
    }

↑所以很多人會尋找第三方套件來處理吧

以下便介紹Json.net，因為威力太強大了~

有了Json.net後就可以使用Json.net的函數產生JSON字串

2. 使用JsonTextWriter

用法很像XmlTextWriter，寫起來有點囉嗦，平常工作我不會用這個


protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)//Get Method
        {
            //準備資料
            string collapse_key = "score_update";
            int time_to_live = 108;
            bool delay_while_idle = true;
            string score = "4x8";
            string time = "15:16.2342";
            List<string> registration_ids = new List<string>() { "4","8","15","16","23","42"};

             
            //要輸出的變數
            StringWriter sw = new StringWriter();
            //建立JsonTextWriter
            JsonTextWriter writer = new JsonTextWriter(sw);
            writer.WriteStartObject();
            writer.WritePropertyName("collapse_key"); writer.WriteValue(collapse_key);
            writer.WritePropertyName("time_to_live"); writer.WriteValue(time_to_live);
            writer.WritePropertyName("delay_while_idle"); writer.WriteValue(delay_while_idle);
            writer.WritePropertyName("data");
            writer.WriteStartObject();
            writer.WritePropertyName("score"); writer.WriteValue(score);
            writer.WritePropertyName("time"); writer.WriteValue(time);
            writer.WriteEndObject();
            writer.WritePropertyName("registration_ids"); 
            writer.WriteStartArray();
            foreach (string item in registration_ids)
            {
                writer.WriteValue(item);
            }
            writer.WriteEndArray();
            writer.WriteEndObject();
 
            //輸出結果
            Response.Write(sw.ToString());
        }
    }

3. 使用JObject匿名物件

比起JsonTextWriter簡化了許多，不過大概是每個Property和值都要再寫一次建構子名稱，我覺得還是有點麻煩


protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)//Get Method
        {
            //準備資料
            string collapse_key = "score_update";
            int time_to_live = 108;
            bool delay_while_idle = true;
            string score = "4x8";
            string time = "15:16.2342";
            List<string> registration_ids = new List<string>() { "4","8","15","16","23","42"};

            //JObject匿名物件
            JObject obj = new JObject(
                 new JProperty("collapse_key",collapse_key),
                 new JProperty("time_to_live",time_to_live),
                 new JProperty("delay_while_idle",delay_while_idle),
                 new JProperty("data",
                     new JObject(
                         new JProperty("score",score),
                         new JProperty("time",time))),
                new JProperty("registration_ids",registration_ids)
                );
 
            //序列化為JSON字串並輸出結果
            Response.Write(JsonConvert.SerializeObject(obj,Formatting.Indented));
        }
    }

那有沒有寫起來直覺，程式碼又短少的方式呢？

請看以下兩個

4. 物件序列化

這個要先知道輸出的json字串長什麼樣子

貼到http://json2csharp.com/去產生類別程式碼

然後


    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)//Get Method
        {
            //準備資料
            string collapse_key = "score_update";
            int time_to_live = 108;
            bool delay_while_idle = true;
            string score = "4x8";
            string time = "15:16.2342";
            List<string> registration_ids = new List<string>() { "4","8","15","16","23","42"};

             
            //建立物件，塞資料
            RootObject root = new RootObject();
            root.collapse_key = collapse_key;
            root.time_to_live = time_to_live;
            root.delay_while_idle = delay_while_idle;
            Data data = new Data();
            root.data = data;
            root.data.score = score;
            root.data.time = time;
            root.registration_ids = registration_ids;
            //物件序列化
            string strJson = JsonConvert.SerializeObject(root, Formatting.Indented); 
            //輸出結果
            Response.Write(strJson);
        }
    }

或使用物件初始化方式塞值


    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)//Get Method
        {
            //準備資料
            string collapse_key = "score_update";
            int time_to_live = 108;
            bool delay_while_idle = true;
            string score = "4x8";
            string time = "15:16.2342";
            List<string> registration_ids = new List<string>() { "4","8","15","16","23","42"};

             
            //建立物件，塞資料
            RootObject root = new RootObject()
            {
                collapse_key = collapse_key,
                time_to_live = time_to_live,
                delay_while_idle = delay_while_idle,
                data = new Data() 
                { 
                   score = score,
                   time=time
                },
                registration_ids = registration_ids
            };
            
            //物件序列化
            string strJson = JsonConvert.SerializeObject(root, Formatting.Indented); 
            //輸出結果
            Response.Write(strJson);
        }
    }

使用物件初始化方式塞值看起來直覺多了

不過為了物件序列化還要特地宣告類別，這…倒不如使用Linq吧

5.用Linq+匿名物件寫法直接組JSON

這招在Json.net的官方文件有範例(用JObject.FromObject的那個)：http://james.newtonking.com/projects/json/help/html/CreatingLINQtoJSON.htm

但只有範例，沒寫為什麼Linq要那樣寫，誰看得懂阿XD

要用Linq直接組JSON

大概把握幾點：

Json Object：Json字串用大括號{}表示，Linq也是用大括號{}表示

Json Object的Name(Key、Property)：Json字串在兩個雙引號””裡寫一個英文單字，Linq就直接寫英文單字即可

Json Array：Json字串用中括號[]表示，Linq就用from o in XXX select o，這種回傳IEnumerable的寫法(如果JSON字串是物件陣列的話就用from o in XXX select new {欄位1=YYY}這種形式)

Json Value：Linq就看Json字串填什麼值就跟著填什麼值


    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)//Get Method
        {
            //準備資料
            List<string> registration_ids = new List<string>() { "4", "8", "15", "16", "23", "42" };

            //用Linq直接組
            var result = new
                            {
                                collapse_key = "score_update",
                                time_to_live = 108,
                                delay_while_idle = true,
                                data = new{
                                    score ="4x8",
                                    time = "15:16.2342"
                                },
                                registration_ids = from s in registration_ids
                                                            select s

                            };

            //序列化為JSON字串並輸出結果
            Response.Write(JsonConvert.SerializeObject(result));
        }
    }

請看圖示解說↓

由於Linq支援DataTable的查詢，所以再難的JSON格式都組得出來，不用再跑for迴圈寫一堆Code，開發速度大幅提昇

以下截自實務上的一段Code(有做了一點修改)


                DataTable dt = new DataTable();//撈出一張資料表的所有數據(這個表類似北風資料庫的員工資料表，有階層關係)
                DataTable dtDetail = new DataTable();//上一張表的一對多明細表
                var firstLevel = dt.Select("pid is NULL");//第一層數據
                var result = new
                {
                      Info = new
                    {
                        Level1 = from a in firstLevel
                                 join b in dt.AsEnumerable() on a.Field<int>("id") equals b.Field<int?>("pid") into secondLevel
                                 select new
                                 { 
                                     Title =  a.Field<string>("Title"),
                                     Level2 = secondLevel.Select(c => new
                                     {
                                         Title =  c.Field<string>("Title"),
                                         Photos = from s in secondLevel 
                                                       join uu in dtDetail.AsEnumerable() on s.Field<int>("id") equals uu.Field<int>("id")
                                                       where s.Field<int>("id") == c.Field<int>("id")
                                                select new
                                                {
                                                    PhotoID = uu.Field<string>("PhotoID"),
                                                    PhotoTitle = uu.Field<string>("PhotoTitle")
                                                }

                                     })
                                 }
                    }
                };

※不過要注意對於寫的人是寫很快，後人維護會有閱讀困難的可能

最後附上一張比較圖

2012.11.09 追記

最後一個方法，直接使用Linq產生Json字串有個缺點要提一下

Linq匿名型別的屬性無法給null值，如下圖

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