Sanuel Jackson Sanuel Jackson - 4 months ago 68
JSON Question

Decoding large Json files in c#

While downloading auction data from blizzard (a 6 MB JSON file), on decode, I was able to trace the error to this :


"Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property.\r\nParameter name: input"


How can I change the maxJsonLength to say 20 MB (as some of the JSON i parse can be that large) in the following class ?

public sealed class DynamicJsonConverter : JavaScriptConverter
{
public override object Deserialize(IDictionary<string, object> dictionary, Type type, JavaScriptSerializer serializer)
{
if (dictionary == null)
throw new ArgumentNullException("dictionary");

return type == typeof(object) ? new DynamicJsonObject(dictionary) : null;
}

public override IDictionary<string, object> Serialize(object obj, JavaScriptSerializer serializer)
{
throw new NotImplementedException();
}

public override IEnumerable<Type> SupportedTypes
{
get { return new ReadOnlyCollection<Type>(new List<Type>(new[] { typeof(object) })); }
}

#region Nested type: DynamicJsonObject

private sealed class DynamicJsonObject : DynamicObject
{
private readonly IDictionary<string, object> _dictionary;

public DynamicJsonObject(IDictionary<string, object> dictionary)
{
if (dictionary == null)
throw new ArgumentNullException("dictionary");
_dictionary = dictionary;
}

public override string ToString()
{
var sb = new StringBuilder("{");
ToString(sb);
return sb.ToString();
}

private void ToString(StringBuilder sb)
{
var firstInDictionary = true;
foreach (var pair in _dictionary)
{
if (!firstInDictionary)
sb.Append(",");
firstInDictionary = false;
var value = pair.Value;
var name = pair.Key;
if (value is string)
{
sb.AppendFormat("{0}:\"{1}\"", name, value);
}
else if (value is IDictionary<string, object>)
{
new DynamicJsonObject((IDictionary<string, object>)value).ToString(sb);
}
else if (value is ArrayList)
{
sb.Append(name + ":[");
var firstInArray = true;
foreach (var arrayValue in (ArrayList)value)
{
if (!firstInArray)
sb.Append(",");
firstInArray = false;
if (arrayValue is IDictionary<string, object>)
new DynamicJsonObject((IDictionary<string, object>)arrayValue).ToString(sb);
else if (arrayValue is string)
sb.AppendFormat("\"{0}\"", arrayValue);
else
sb.AppendFormat("{0}", arrayValue);

}
sb.Append("]");
}
else
{
sb.AppendFormat("{0}:{1}", name, value);
}
}
sb.Append("}");
}

public override bool TryGetMember(GetMemberBinder binder, out object result)
{
if (!_dictionary.TryGetValue(binder.Name, out result))
{
// return null to avoid exception. caller can check for null this way...
result = null;
return true;
}

result = WrapResultObject(result);
return true;
}

public override bool TryGetIndex(GetIndexBinder binder, object[] indexes, out object result)
{
if (indexes.Length == 1 && indexes[0] != null)
{
if (!_dictionary.TryGetValue(indexes[0].ToString(), out result))
{
// return null to avoid exception. caller can check for null this way...
result = null;
return true;
}

result = WrapResultObject(result);
return true;
}

return base.TryGetIndex(binder, indexes, out result);
}

private static object WrapResultObject(object result)
{
var dictionary = result as IDictionary<string, object>;
if (dictionary != null)
return new DynamicJsonObject(dictionary);

var arrayList = result as ArrayList;
if (arrayList != null && arrayList.Count > 0)
{
return arrayList[0] is IDictionary<string, object>
? new List<object>(arrayList.Cast<IDictionary<string, object>>().Select(x => new DynamicJsonObject(x)))
: new List<object>(arrayList.Cast<object>());
}

return result;
}
}

#endregion
}


or in the calling method :

public static dynamic DecodeJson(this string str)
{
var serializer = new JavaScriptSerializer();
serializer.RegisterConverters(new[] { new DynamicJsonConverter() });
dynamic result = null;
try
{
result = serializer.Deserialize(str, typeof(object));
} catch (ArgumentException ae)
{
Log.Output(ae.InnerException.Message);
}
return result;
}

Answer

You should modify the JavaScriptSerializer.MaxJsonLength Property

The maximum length of JSON strings. The default is 2097152 characters, which is equivalent to 4 MB of Unicode string data.

public static dynamic DecodeJson(this string str)
{
    var serializer = new JavaScriptSerializer();
    serializer.MaxJsonLength = Int.MaxValue; // The value of this constant is 2,147,483,647
    serializer.RegisterConverters(new[] { new DynamicJsonConverter() });
    dynamic result = null;
    try
    {
        result = serializer.Deserialize(str, typeof(object));
    } catch (ArgumentException ae)
    {
        Log.Output(ae.InnerException.Message);
    }
    return result;
}