我可以使用流解压缩和反序列化文件吗？

Question

我的应用程序使用 Json.Net 序列化一个对象，压缩生成的 JSON，然后将其保存到文件中。此外，应用程序可以从这些文件之一加载对象。这些对象的大小可能为数十 Mb，由于现有代码创建大字符串和字节数组的方式，我担心内存使用情况：-

public void Save(MyClass myObject, string filename)
{
    var json = JsonConvert.SerializeObject(myObject);
    var bytes = Compress(json);
    File.WriteAllBytes(filename, bytes);
}

public MyClass Load(string filename)
{    
    var bytes = File.ReadAllBytes(filename);
    var json = Decompress(bytes);
    var myObject = JsonConvert.DeserializeObject<MyClass>(json);
}

private static byte[] Compress(string s)
{
    var bytes = Encoding.Unicode.GetBytes(s);

    using (var ms = new MemoryStream())
    {
        using (var gs = new GZipStream(ms, CompressionMode.Compress))
        {
            gs.Write(bytes, 0, bytes.Length);
            gs.Close();
            return ms.ToArray();
        }
    }
}

private static string Decompress(byte[] bytes)
{
    using (var msi = new MemoryStream(bytes))
    {
        using (var mso = new MemoryStream())
        {
            using (var gs = new GZipStream(msi, CompressionMode.Decompress))
            {
                gs.CopyTo(mso);
                return Encoding.Unicode.GetString(mso.ToArray());
            }
        }
    } 
}

我想知道是否可以将 Save/Load 方法替换为流？我找到了在 Json.Net 中使用流的示例，但我正在努力弄清楚如何适应额外的压缩内容。

Answer 1

JsonSerializer 具有从JsonTextReader 和StreamWriter 序列化的方法，这两种方法都可以在任何类型的流之上创建，包括GZipStream。使用它们，您可以创建以下扩展方法：

public static partial class JsonExtensions
{
    // Buffer sized as recommended by Bradley Grainger, https://faithlife.codes/blog/2012/06/always-wrap-gzipstream-with-bufferedstream/
    // But anything smaller than 85,000 bytes should be OK, since objects larger than that go on the large object heap.  See:
    // https://docs.microsoft.com/en-us/dotnet/standard/garbage-collection/large-object-heap
    const int BufferSize = 8192;
    // Disable writing of BOM as per https://datatracker.ietf.org/doc/html/rfc8259#section-8.1
    static readonly Encoding DefaultEncoding = new UTF8Encoding(false);

    public static void SerializeToFileCompressed(object value, string path, JsonSerializerSettings settings = null)
    {
        using (var fs = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.Read))
            SerializeCompressed(value, fs, settings);
    }

    public static void SerializeCompressed(object value, Stream stream, JsonSerializerSettings settings = null)
    {
        using (var compressor = new GZipStream(stream, CompressionMode.Compress))
        using (var writer = new StreamWriter(compressor, DefaultEncoding, BufferSize))
        {
            var serializer = JsonSerializer.CreateDefault(settings);
            serializer.Serialize(writer, value);
        }
    }

    public static T DeserializeFromFileCompressed<T>(string path, JsonSerializerSettings settings = null)
    {
        using (var fs = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read))
            return DeserializeCompressed<T>(fs, settings);
    }

    public static T DeserializeCompressed<T>(Stream stream, JsonSerializerSettings settings = null)
    {
        using (var compressor = new GZipStream(stream, CompressionMode.Decompress))
        using (var reader = new StreamReader(compressor))
        using (var jsonReader = new JsonTextReader(reader))
        {
            var serializer = JsonSerializer.CreateDefault(settings);
            return serializer.Deserialize<T>(jsonReader);
        }
    }
}

请参阅 Json.NET 文档中的 Performance Tips: Optimize Memory Usage。

Answer 2

对于那些想知道如何在 uwp 应用程序中使用来自 @dbc 的扩展名的人，我将代码修改为 - 其中 StorageFile 是您有权写入的文件。

public static async void SerializeToFileCompressedAsync(object value, StorageFile file, JsonSerializerSettings settings = null)
{
    using (var stream = await file.OpenStreamForWriteAsync())
        SerializeCompressed(value, stream, settings);
}

public static void SerializeCompressed(object value, Stream stream, JsonSerializerSettings settings = null)
{
    using (var compressor = new GZipStream(stream, CompressionMode.Compress))
    using (var writer = new StreamWriter(compressor))
    {
        var serializer = JsonSerializer.CreateDefault(settings);
        serializer.Serialize(writer, value);
    }
}

public static async Task<T> DeserializeFromFileCompressedAsync<T>(StorageFile file, JsonSerializerSettings settings = null)
{
    using (var stream = await file.OpenStreamForReadAsync())
        return DeserializeCompressed<T>(stream, settings);
}

public static T DeserializeCompressed<T>(Stream stream, JsonSerializerSettings settings = null)
{
    using (var compressor = new GZipStream(stream, CompressionMode.Decompress))
    using (var reader = new StreamReader(compressor))
    using (var jsonReader = new JsonTextReader(reader))
    {
        var serializer = JsonSerializer.CreateDefault(settings);
        return serializer.Deserialize<T>(jsonReader);
    }
}