How can I deserialize JSON to a simple Dictionary<

Question

I have a simple key/value list in JSON being sent back to ASP.NET via POST. Example:

{ "key1": "value1", "key2": "value2"}

I AM NOT TRYING TO DESERIALIZE INTO STRONGLY-TYPED .NET OBJECTS

I simply need a plain old Dictionary(Of String, String), or some equivalent (hash table, Dictionary(Of String, Object), old-school StringDictionary--hell, a 2-D array of strings would work for me.

I can use anything available in ASP.NET 3.5, as well as the popular Json.NET (which I'm already using for serialization to the client).

Apparently neither of these JSON libraries have this forehead-slapping obvious capability out of the box--they are totally focused on reflection-based deserialization via strong contracts.

Any ideas?

Limitations:

1. I don't want to implement my own JSON parser
2. Can't use ASP.NET 4.0 yet
3. Would prefer to stay away from the older, deprecated ASP.NET class for JSON

Answer 1

I did discover .NET has a built in way to cast the JSON string into a Dictionary<String, Object> via the System.Web.Script.Serialization.JavaScriptSerializer type in the 3.5 System.Web.Extensions assembly. Use the method DeserializeObject(String).

I stumbled upon this when doing an ajax post (via jquery) of content type 'application/json' to a static .net Page Method and saw that the method (which had a single parameter of type Object) magically received this Dictionary.

Answer 2

You could use Tiny-JSON

string json = "{\"key1\":\"value1\", \"key2\":\"value2\"}";
IDictionary<string, string> dict = Tiny.Json.Decode<Dictionary<string, string>>(json);

Answer 3

Edit: This works, but the accepted answer using Json.NET is much more straightforward. Leaving this one in case someone needs BCL-only code.

It’s not supported by the .NET framework out of the box. A glaring oversight – not everyone needs to deserialize into objects with named properties. So I ended up rolling my own:

<Serializable()> Public Class StringStringDictionary
    Implements ISerializable
    Public dict As System.Collections.Generic.Dictionary(Of String, String)
    Public Sub New()
        dict = New System.Collections.Generic.Dictionary(Of String, String)
    End Sub
    Protected Sub New(info As SerializationInfo, _
          context As StreamingContext)
        dict = New System.Collections.Generic.Dictionary(Of String, String)
        For Each entry As SerializationEntry In info
            dict.Add(entry.Name, DirectCast(entry.Value, String))
        Next
    End Sub
    Public Sub GetObjectData(info As SerializationInfo, context As StreamingContext) Implements ISerializable.GetObjectData
        For Each key As String in dict.Keys
            info.AddValue(key, dict.Item(key))
        Next
    End Sub
End Class

Called with:

string MyJsonString = "{ \"key1\": \"value1\", \"key2\": \"value2\"}";
System.Runtime.Serialization.Json.DataContractJsonSerializer dcjs = new
  System.Runtime.Serialization.Json.DataContractJsonSerializer(
    typeof(StringStringDictionary));
System.IO.MemoryStream ms = new
  System.IO.MemoryStream(Encoding.UTF8.GetBytes(MyJsonString));
StringStringDictionary myfields = (StringStringDictionary)dcjs.ReadObject(ms);
Response.Write("Value of key2: " + myfields.dict["key2"]);

Sorry for the mix of C# and VB.NET…

Answer 4

It seems all of these answers here just assume you can get that little string out of a bigger object... for people looking to simply deserealize a large object with such a dictionary somewhere inside the mapping, and who are using the System.Runtime.Serialization.Json DataContract system, here's a solution:

An answer on gis.stackexchange.com had this interesting link. I had to recover it with archive.org, but it offers a pretty much perfect solution: a custom IDataContractSurrogate class in which you implement exactly your own types. I was able to expand it easily.

I made a bunch of changes in it, though. Since the original source is no longer available, I'll post the entire class here:

using System;
using System.CodeDom;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Json;
using System.Text;

namespace JsonTools
{
    /// <summary>
    /// Allows using Dictionary&lt;String,String&gt; and Dictionary&lt;String,Boolean&gt; types, and any others you'd like to add.
    /// Source: https://web.archive.org/web/20100317222656/my6solutions.com/post/2009/06/30/DataContractSerializer-DataContractJsonSerializer-JavaScriptSerializer-XmlSerializer-for-serialization.aspx
    /// </summary>
    public class JsonSurrogate : IDataContractSurrogate
    {
        /// <summary>
        /// Deserialize an object with added support for the types defined in this class.
        /// </summary>
        /// <typeparam name="T">Contract class</typeparam>
        /// <param name="json">JSON String</param>
        /// <param name="encoding">Text encoding</param>
        /// <returns>The deserialized object of type T</returns>
        public static T Deserialize<T>(String json, Encoding encoding)
        {
            if (encoding == null)
                encoding = new UTF8Encoding(false);
            DataContractJsonSerializer deserializer = new DataContractJsonSerializer(
                typeof(T), new Type[0], int.MaxValue, true, new JsonSurrogate(), false);
            using (MemoryStream stream = new MemoryStream(encoding.GetBytes(json)))
            {
                T result = (T)deserializer.ReadObject(stream);
                return result;
            }
        }

        // make sure all values in this are classes implementing JsonSurrogateObject.
        private static Dictionary<Type, Type> KnownTypes = 
            new Dictionary<Type, Type>()
            {
                {typeof(Dictionary<String, String>), typeof(SSDictionary)},
                {typeof(Dictionary<String, Boolean>), typeof(SBDictionary)}
            };

        #region Implemented surrogate dictionary classes

        [Serializable]
        public class SSDictionary : SurrogateDictionary<String>
        {
            public SSDictionary() : base() {}
            protected SSDictionary (SerializationInfo info, StreamingContext context) : base(info, context) {}
        }
        [Serializable]
        public class SBDictionary : SurrogateDictionary<Boolean>
        {
            public SBDictionary() : base() {}
            protected SBDictionary (SerializationInfo info, StreamingContext context) : base(info, context) {}
        }

        #endregion

        /// <summary>Small interface to easily extract the final value from the object.</summary>
        public interface JsonSurrogateObject
        {
            Object DeserializedObject { get; }
        }

        /// <summary>
        /// Class for deserializing any simple dictionary types with a string as key.
        /// </summary>
        /// <typeparam name="T">Any simple type that will be deserialized correctly.</typeparam>
            [Serializable]
        public abstract class SurrogateDictionary<T> : ISerializable, JsonSurrogateObject
        {
            public Object DeserializedObject { get { return dict; } }
            private Dictionary<String, T> dict;

            public SurrogateDictionary()
            {
                dict = new Dictionary<String, T>();
            }

            // deserialize
            protected SurrogateDictionary(SerializationInfo info, StreamingContext context)
            {
                dict = new Dictionary<String, T>();
                foreach (SerializationEntry entry in info)
                {
                    // This cast will only work for base types, of course.
                    dict.Add(entry.Name, (T)entry.Value);
                }
            }
            // serialize
            public void GetObjectData(SerializationInfo info, StreamingContext context)
            {
                foreach (String key in dict.Keys)
                {
                    info.AddValue(key, dict[key]);
                }
            }

        }

        /// <summary>
            /// Uses the KnownTypes dictionary to get the surrogate classes.
        /// </summary>
        /// <param name="type"></param>
        /// <returns></returns>
        public Type GetDataContractType(Type type)
        {
            Type returnType;
            if (KnownTypes.TryGetValue(type, out returnType))
            {
                return returnType;
            }
            return type;
        }

        public object GetObjectToSerialize(object obj, Type targetType)
        {
            throw new NotImplementedException();
        }

        /// <summary>
        ///     Gets the object out of the surrogate datacontract object. This function is the reason all surrogate objects need to implement the JsonSurrogateObject class.
        /// </summary>
        /// <param name="obj">Result of the deserialization</param>
        /// <param name="targetType">Expected target type of the deserialization</param>
        /// <returns></returns>
        public object GetDeserializedObject(object obj, Type targetType)
        {
            if (obj is JsonSurrogateObject)
            {
                return ((JsonSurrogateObject)obj).DeserializedObject;
            }
            return obj;
        }

        public Type GetReferencedTypeOnImport(string typeName, string typeNamespace, object customData)
        {
            return null;
        }

        #region not implemented

        public object GetCustomDataToExport(MemberInfo memberInfo, Type dataContractType)
        {
            throw new NotImplementedException();
        }

        public object GetCustomDataToExport(Type clrType, Type dataContractType)
        {
            throw new NotImplementedException();
        }

        public void GetKnownCustomDataTypes(Collection<Type> customDataTypes)
        {
            throw new NotImplementedException();
        }

        public CodeTypeDeclaration ProcessImportedType(CodeTypeDeclaration typeDeclaration, CodeCompileUnit compileUnit)
        {
            throw new NotImplementedException();
        }

        #endregion
    }
}

To add new supported types to the class, you just need to add your class, give it the right constructors and functions (look at SurrogateDictionary for an example), make sure it inherits JsonSurrogateObject, and add its type mapping to the KnownTypes dictionary. The included SurrogateDictionary can serve as basis for any Dictionary<String,T> types where T is any type that does deserialize correctly.

Calling it is really simple:

MyObjtype newObj = JsonSurrogate.Deserialize<MyObjtype>(jsonStr, encoding);

Note that for some reason this thing has trouble using key strings which contain spaces; they were simply not present in the final list. Might just be it's simply against json specs and the api I was calling was poorly implemented, mind you; I dunno. Anyway, I solved this by regex-replacing them with underscores in the raw json data and fixing the dictionary after the deserialization.

Answer 5

I just implemented this in RestSharp. This post was helpful to me.

Besides the code in the link, here is my code. I now get a Dictionary of results when I do something like this:

var jsonClient = new RestClient(url.Host);
jsonClient.AddHandler("application/json", new DynamicJsonDeserializer());
var jsonRequest = new RestRequest(url.Query, Method.GET);
Dictionary<string, dynamic> response = jsonClient.Execute<JObject>(jsonRequest).Data.ToObject<Dictionary<string, dynamic>>();

Be mindful of the sort of JSON you're expecting - in my case, I was retrieving a single object with several properties. In the attached link, the author was retrieving a list.

Answer 6

If you're after a lightweight, no-added-references kind of approach, maybe this bit of code I just wrote will work (I can't 100% guarantee robustness though).

using System;
using System.Collections.Generic;
using System.Text;
using System.Text.RegularExpressions;

public Dictionary<string, object> ParseJSON(string json)
{
    int end;
    return ParseJSON(json, 0, out end);
}
private Dictionary<string, object> ParseJSON(string json, int start, out int end)
{
    Dictionary<string, object> dict = new Dictionary<string, object>();
    bool escbegin = false;
    bool escend = false;
    bool inquotes = false;
    string key = null;
    int cend;
    StringBuilder sb = new StringBuilder();
    Dictionary<string, object> child = null;
    List<object> arraylist = null;
    Regex regex = new Regex(@"\\u([0-9a-z]{4})", RegexOptions.IgnoreCase);
    int autoKey = 0;
    for (int i = start; i < json.Length; i++)
    {
        char c = json[i];
        if (c == '\\') escbegin = !escbegin;
        if (!escbegin)
        {
            if (c == '"')
            {
                inquotes = !inquotes;
                if (!inquotes && arraylist != null)
                {
                    arraylist.Add(DecodeString(regex, sb.ToString()));
                    sb.Length = 0;
                }
                continue;
            }
            if (!inquotes)
            {
                switch (c)
                {
                    case '{':
                        if (i != start)
                        {
                            child = ParseJSON(json, i, out cend);
                            if (arraylist != null) arraylist.Add(child);
                            else
                            {
                                dict.Add(key, child);
                                key = null;
                            }
                            i = cend;
                        }
                        continue;
                    case '}':
                        end = i;
                        if (key != null)
                        {
                            if (arraylist != null) dict.Add(key, arraylist);
                            else dict.Add(key, DecodeString(regex, sb.ToString()));
                        }
                        return dict;
                    case '[':
                        arraylist = new List<object>();
                        continue;
                    case ']':
                        if (key == null)
                        {
                            key = "array" + autoKey.ToString();
                            autoKey++;
                        }
                        if (arraylist != null && sb.Length > 0)
                        {
                            arraylist.Add(sb.ToString());
                            sb.Length = 0;
                        }
                        dict.Add(key, arraylist);
                        arraylist = null;
                        key = null;
                        continue;
                    case ',':
                        if (arraylist == null && key != null)
                        {
                            dict.Add(key, DecodeString(regex, sb.ToString()));
                            key = null;
                            sb.Length = 0;
                        }
                        if (arraylist != null && sb.Length > 0)
                        {
                            arraylist.Add(sb.ToString());
                            sb.Length = 0;
                        }
                       continue;
                    case ':':
                        key = DecodeString(regex, sb.ToString());
                        sb.Length = 0;
                        continue;
                }
            }
        }
        sb.Append(c);
        if (escend) escbegin = false;
        if (escbegin) escend = true;
        else escend = false;
    }
    end = json.Length - 1;
    return dict; //theoretically shouldn't ever get here
}
private string DecodeString(Regex regex, string str)
{
    return Regex.Unescape(regex.Replace(str, match => char.ConvertFromUtf32(Int32.Parse(match.Groups[1].Value, System.Globalization.NumberStyles.HexNumber))));
}

[I realise that this violates the OP Limitation #1, but technically, you didn't write it, I did]