CODEWITHSUNDEEP
c#json.net
Andrey Shchekin
Andrey Shchekin

Reputation: 21599

What is the correct way to use JSON.NET to parse stream of JSON objects?

I have a stream of JSON objects that looks somewhat like this:

{...}{...}{...}{...}...

So basically a concatenated list of JSON objects without any separator. What's the proper way to deserialize those into an IEnumerable<T> using JSON.NET? At the moment I tried something like 

var serializer = new JsonSerializer();
serializer.CheckAdditionalContent = false;

using (var reader = new StreamReader(stream))
using (var jsonReader = new JsonTextReader(reader)) {
    reader.SupportMultipleContent = true;
    reader.Read();
    while (reader.TokenType != JsonToken.None) {
        yield return serializer.Deserialize<TResult>(reader);
    }
}

But this fails with

Newtonsoft.Json.JsonSerializationException: Unexpected token while deserializing object: EndObject. Path '', line 1, position 55.
  at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue)
  at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
  at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
  at Newtonsoft.Json.JsonSerializer.Deserialize[T](JsonReader reader)

Obviously I need to move the reader after the Deserialize call, but how do I do this?

Upvotes: 15

Views: 14880

Answers (1)

Andrew Whitaker
Andrew Whitaker

Reputation: 126052

I think if you change your loop around slightly everything should work:

public IEnumerable<TResult> ReadJson<TResult>(Stream stream)
{
    var serializer = new JsonSerializer();

    using (var reader = new StreamReader(stream))
    using (var jsonReader = new JsonTextReader(reader))
    {
        jsonReader.SupportMultipleContent = true;

        while (jsonReader.Read())
        {
            yield return serializer.Deserialize<TResult>(jsonReader);
        }
    }
}

Note that you must iterate over the IEnumerable<TResult> while the Stream passed to this method is open:

using (var stream = /* some stream */)
{
    IEnumerable<MyClass> result = ReadJson<MyClass>(stream);

    foreach (var item in result)
    {
        Console.WriteLine(item.MyProperty);
    }
}

Example: https://dotnetfiddle.net/Y2FLuK

Sample on JsonNet site: Read Multiple Fragments With JsonReader

Upvotes: 20

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