How Can Json.NET Stream Deserialize Large JSON Files Efficiently to Minimize Memory Usage?

Json.NET streaming deserialization: efficient processing of large JSON files

For huge JSON files containing lots of identical objects, it is crucial to avoid loading the entire file into memory. Json.NET provides a way to deserialize JSON content directly from the stream, significantly reducing memory consumption.

Initial attempts and limitations

Deserializing the object directly in the loop will treat the file as a single object, which will fail due to the presence of the root JSON list. Deserializing JSON into a C# list, while it is possible to read items one by one, still consumes a lot of memory because the list holds all deserialized objects.

Streaming Deserialization

In order to read objects in the stream sequentially, the starting position of each object needs to be identified and deserialized accordingly. This can be achieved by using the reader.TokenType attribute within a loop:

JsonSerializer serializer = new JsonSerializer();
MyObject o;
using (FileStream s = File.Open("bigfile.json", FileMode.Open))
using (StreamReader sr = new StreamReader(s))
using (JsonReader reader = new JsonTextReader(sr))
{
    while (reader.Read())
    {
        if (reader.TokenType == JsonToken.StartObject)
        {
            o = serializer.Deserialize<MyObject>(reader);
            // 处理对象 o
        }
    }
}

This code only deserializes when the reader encounters the beginning of the object ({). Skipping other markers ensures efficient parsing of large files without consuming unnecessary RAM. The // 处理对象 o comment is added to the code to remind readers that the read MyObject object needs to be actually processed after deserialization.

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