将 JSON 写入流而不在内存中缓冲字符串 [英] Writing JSON to a stream without buffering the string in memory

问题描述

我想通过显式构建文档将 JSON 写入 Stream.例如:

var stream = ...;var writer = new JsonWriter(stream);writer.BeginArray();{writer.BeginObject();{writer.String("foo");writer.Number(1);writer.String("bar");writer.Number(2.3);}writer.EndObject();}writer.EndArray();

这将产生:

<预><代码>[{富":1，酒吧":2.3}]

这种方法的好处是不需要在内存中缓冲任何东西.在我的情况下，我正在向流中写入大量 JSON.诸如这个之类的解决方案涉及在内存中创建所有对象，然后将它们序列化为内存中的大字符串，最后写入这个字符串到流和垃圾收集，可能来自 LOH.我想保持较低的内存使用率，在从另一个文件/DB/etc 流读取数据时写出元素.

这种方法可通过 rapidjson 库在 C++ 中使用.

我已经为此搜索了很多，但没有找到解决方案.

解决方案

原来我需要在 Google 上使用一段时间.

JSON.NET 确实通过其 JsonWriter 支持这一点 类.

我的例子会写成:

Stream stream = ...;使用 (var streamWriter = new StreamWriter(stream))使用 (var writer = new JsonTextWriter(streamWriter)){writer.Formatting = Formatting.Indented;writer.WriteStartArray();{writer.WriteStartObject();{writer.WritePropertyName("foo");writer.WriteValue(1);writer.WritePropertyName("bar");writer.WriteValue(2.3);}writer.WriteEndObject();}writer.WriteEndArray();}

I would like to write JSON to a Stream by building the document up explicitly. For example:

var stream = ...;
var writer = new JsonWriter(stream);

writer.BeginArray();
{
  writer.BeginObject();
  {
    writer.String("foo");
    writer.Number(1);
    writer.String("bar");
    writer.Number(2.3);
  }
  writer.EndObject();
}
writer.EndArray();

This would produce:

[
  {
    "foo": 1,
    "bar": 2.3
  }
]

The benefit of this approach is that nothing needs to be buffered in memory. In my situation, I'm writing quite a lot of JSON to the stream. Solutions such as this one involve creating all your objects in memory, then serialising them to a large string in memory, then finally writing this string to the stream and garbage collecting, probably from the LOH. I want to keep my memory use low, writing out elements while reading data from another file/DB/etc stream.

This kind of approach is available in C++ via the rapidjson library.

I've searched around a fair bit for this and haven't found a solution.

解决方案

Turns out I needed to Google for a bit longer.

JSON.NET does indeed support this via its JsonWriter class.

My example would be written:

Stream stream = ...;

using (var streamWriter = new StreamWriter(stream))
using (var writer = new JsonTextWriter(streamWriter))
{
    writer.Formatting = Formatting.Indented;

    writer.WriteStartArray();
    {
        writer.WriteStartObject();
        {
            writer.WritePropertyName("foo");
            writer.WriteValue(1);
            writer.WritePropertyName("bar");
            writer.WriteValue(2.3);
        }
        writer.WriteEndObject();
    }
    writer.WriteEndArray();
}

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