In my previous article I talked about the hunt for a good JSON parser/serializer. For my current project I only needed a serializer to generate JSON from any .NET object, so for now it’s a bit overkill to use a full blown JSON library.

After looking at the specs for JSON, I figured it couldn’t be too hard to write a JSON serializer in C#. Not only was it not that hard, it was very short too: about 100 lines of code (well, 110 without the empty lines).

The serializer can handle any regular data type, including DateTime (for which there is no standard in JSON).

Here it is: (feel free to use it for anything you like)

public class JSONSerializer
{
    private readonly StringBuilder _output = new StringBuilder();

    public static string ToJSON(object obj)
    {
        return new JSONSerializer().ConvertToJSON(obj);
    }

    private string ConvertToJSON(object obj)
    {
        WriteValue(obj);

        return _output.ToString();
    }

    private void WriteValue(object obj)
    {
        if (obj == null)
            _output.Append("null");
        else if (obj is sbyte || obj is byte || obj is short || obj is ushort || obj is int || obj is uint || obj is long || obj is ulong || obj is decimal || obj is double || obj is float)
            _output.Append(Convert.ToString(obj,NumberFormatInfo.InvariantInfo));
        else if (obj is bool)
            _output.Append(obj.ToString().ToLower());
        else if (obj is char || obj is Enum || obj is Guid)
            WriteString("" + obj);
        else if (obj is DateTime)
            _output.Append("new Date(" + ((DateTime)obj - new DateTime(1970,1,1)).TotalMilliseconds.ToString("0") + ")");
        else if (obj is string)
            WriteString((string)obj);
        else if (obj is IDictionary)
            WriteDictionary((IDictionary)obj);
        else if (obj is Array || obj is IList || obj is ICollection)
            WriteArray((IEnumerable)obj);
        else
            WriteObject(obj);
    }

    private void WriteObject(object obj)
    {
        _output.Append("{ ");

        bool pendingSeparator = false;

        foreach (FieldInfo field in obj.GetType().GetFields(BindingFlags.Public|BindingFlags.Instance))
        {
            if (pendingSeparator)
                _output.Append(" , ");

            WritePair(field.Name, field.GetValue(obj));

            pendingSeparator = true;
        }

        foreach (PropertyInfo property in obj.GetType().GetProperties(BindingFlags.Public | BindingFlags.Instance))
        {
            if (!property.CanRead)
                continue;

            if (pendingSeparator)
                _output.Append(" , ");

            WritePair(property.Name,property.GetValue(obj, null));

            pendingSeparator = true;
        }

        _output.Append(" }");
    }

    private void WritePair(string name, object value)
    {
        WriteString(name);

        _output.Append(" : ");

        WriteValue(value);
    }

    private void WriteArray(IEnumerable array)
    {
        _output.Append("[ ");

        bool pendingSeperator = false;

        foreach (object obj in array)
        {
            if (pendingSeperator)
                _output.Append(',');

            WriteValue(obj);

            pendingSeperator = true;
        }

        _output.Append(" ]");
    }

    private void WriteDictionary(IDictionary dic)
    {
        _output.Append("{ ");

        bool pendingSeparator = false;

        foreach (DictionaryEntry entry in dic)
        {
            if (pendingSeparator)
                _output.Append(" , ");

            WritePair(entry.Key.ToString(),entry.Value);

            pendingSeparator = true;
        }

        _output.Append(" }");
    }

    private void WriteString(string s)
    {
        _output.Append('\"');

        foreach (char c in s)
        {
            switch (c)
            {
                case '\t': _output.Append("\\t"); break;
                case '\r': _output.Append("\\r"); break;
                case '\n': _output.Append("\\n"); break;
                case '"': 
                case '\\': _output.Append("\\" + c); break;
                default:
                    {
                        if (c >= ' ' && c < 128)
                            _output.Append(c);
                        else
                            _output.Append("\\u" + ((int) c).ToString("X4"));
                    }
                    break;
            }
        }

        _output.Append('\"');
    }
}

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