How to Parse Large, Invalid JSON Files in .NET with JSON.NET?

Parsing Large Invalid JSON Files in .NET with JSON.NET

In this article, we will address the challenge of parsing large JSON files that may contain invalid syntax or specific formats not natively supported by Json.NET.

The issue arises when JSON data consists of multiple arrays separated by closing and opening brackets instead of being nested within a single array. This deviation from standard JSON syntax can cause difficulties for Json.NET's built-in deserialization methods.

Json.NET and Invalid JSON Data

Initially, using JsonConvert.DeserializeObject to parse large JSON files can lead to exceptions when the data exceeds memory limits. Similarly, attempting to deserialize directly to a JArray may also result in errors.

Resolving the Parsing Issue

To handle this scenario effectively, we will utilize a customized approach involving JsonTextReader. By setting the SupportMultipleContent flag to true, the reader can recognize the invalid JSON format and treat each array as a separate content section.

Parsing the Invalid JSON Data

The following C# code demonstrates how to implement this technique:

using (WebClient client = new WebClient())
using (Stream stream = client.OpenRead(stringUrl))
using (StreamReader streamReader = new StreamReader(stream))
using (JsonTextReader reader = new JsonTextReader(streamReader))
{
    reader.SupportMultipleContent = true;

    var serializer = new JsonSerializer();
    while (reader.Read())
    {
        if (reader.TokenType == JsonToken.StartObject)
        {
            Contact c = serializer.Deserialize<Contact>(reader);
            Console.WriteLine(c.FirstName + " " + c.LastName);
        }
    }
}

By accessing each array independently using this method, we can efficiently deserialize the JSON data line by line, effectively overcoming the memory and syntax limitations encountered with standard Json.NET parsing methods.

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