我可以使用流对文件进行解压缩和反序列化吗？

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。另外，应用程序可以从这些文件之一加载对象。这些对象可以在大小几十MB，我很担心内存使用情况，由于道路现有的代码创建大型字符串和字节数组： -

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()); 
      } 
     } 
    } 
} 

我在想，如果在保存/载入的方法可以被流替换？我已经找到了与Json.Net一起使用流的例子，但我正在努力弄清楚如何适应额外的压缩内容。

Answer 1

JsonSerializer有从JsonTextReader和StreamWriter序列化的方法，这两种方法都可以在任何种类的流的顶部创建，包括GZipStream。使用它们，您可以创建以下扩展方法：

public static class JsonExtensions 
{ 
    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)) 
     { 
      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

对于那些正在寻找如何在uwp应用程序中使用@dbc扩展的想法，我将代码修改为此 - 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); 
    } 
}