How to Efficiently Parse Large JSON Files as a Stream in Json.NET?

Json.NET streaming for large JSON files

When dealing with very large JSON files containing many identical objects, efficient parsing without overloading memory is crucial. One approach is to parse the file as a stream, reading and processing one object at a time.

Challenges of direct deserialization

Initially, trying to deserialize the object directly using JsonSerializer.Deserialize<myobject>(reader) will fail because the JSON file contains a list of objects, not a single object. While deserializing the objects into a list solved the problem, it resulted in excessive RAM usage since the list retained all deserialized objects.

Stream-based method

To deal with these challenges, a more efficient approach is to parse the file as a stream, reading each object one by one. The following C# code demonstrates this approach:

<code class="language-csharp">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())
    {
        // 当读取器遇到“{”字符时才进行反序列化
        if (reader.TokenType == JsonToken.StartObject)
        {
            o = serializer.Deserialize<myobject>(reader);
            // 处理对象 o，例如将其写入数据库或其他地方
        }
    }
}</code>

In this solution, the stream advances character by character until the reader encounters the opening brace "{" indicating the beginning of the object. Then use the Deserialize method to deserialize the object. Once an object is processed, it is discarded from RAM, allowing the next object to be read without keeping the entire file in memory.

Advantages based on stream parsing

This flow-based approach has significant advantages:

• Efficient memory management: Minimizes memory usage by reading and processing one object at a time.
• Scalability: It can handle very large JSON files without running into memory issues.
• Flexibility: The code can be easily adjusted to handle different object structures by modifying the deserialization logic.

Conclusion

Parse large JSON files as streams in Json.NET, with the ability to efficiently process individual objects without overloading RAM. This approach is especially useful when memory usage is limited.

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