How Can I Parse Large JSON Streams Efficiently with Limited RAM in Json.NET?

Json.NET processing large JSON streams in a memory-constrained environment

Parsing JSON files containing a large number of similar objects is a challenge in a memory-constrained environment. Consider the following scenario:

A huge JSON file contains many JSON objects with the same structure. If each object is a separate file, you can deserialize the objects one by one. However, due to the nested nature of the data, directly deserializing a JSON array of these objects will throw an exception saying an object was expected rather than a list.

Attempting to deserialize the entire JSON file into a list of C# objects successfully avoids the problem of reading the entire JSON file into RAM. However, it introduces a new problem of creating a C# list object that still holds all the data from the JSON file in memory.

To overcome these limitations, a strategy is needed to read objects one at a time. This approach eliminates the need to load the entire JSON string or all data into RAM as a C# object.

Solution

The following code example illustrates this approach:

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())
    {
        // 只在流中存在"{"字符时才反序列化
        if (reader.TokenType == JsonToken.StartObject)
        {
            o = serializer.Deserialize<MyObject>(reader);
            // 对o进行处理
        }
    }
}

This code simulates the initial method of deserializing the object in a loop, but it only deserializes the object when the reader encounters a "{" character in the stream. This approach efficiently processes JSON streams without overusing RAM by skipping to the next object until another starting object marker is found. Note that myobject in the code has been corrected to MyObject, and comments on the processing of the o object have been added to facilitate users to add subsequent operations according to the actual situation.

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