System.Text.Json 无法访问处置 jsonDocument

Question

有人可以帮我解决这个错误吗？直到现在我都无法解决这个问题。我不知道问题出在哪里。

“无法访问已释放的对象。对象名称：'JsonDocument'”

我刚开始使用“Sytem.Text.Json”，这就是我仍在学习并想知道如何正确使用它的原因。

谢谢。

  public static async Task<JsonElement> ParseJsonData(string api, CancellationToken ct)
    {
        clientHandler = new HttpClientHandler()
        {
            UseProxy = Proxy.IsUseProxy ? true : false,
            Proxy = Proxy.IsUseProxy ? new WebProxy($"{Proxy.ProxyHost}:{Proxy.ProxyPort}") : null,
            //ServerCertificateCustomValidationCallback = (sender, certificate, chain, errors) => { return true; },
            // SslProtocols = SslProtocols.Tls12 | SslProtocols.Tls11 | SslProtocols.Tls
        };
        var uri = new Uri(api, UriKind.Absolute);
        utils.SetConnection(uri);
        client = new HttpClient(clientHandler);
        using (var request = new HttpRequestMessage(HttpMethod.Get, uri))
        {
            AddRequestHeaders(request, uri);
            return await ResponseMessage(request, ct);
        }
    }
    private static async Task<JsonElement> ResponseMessage(HttpRequestMessage request, CancellationToken ct)
    {
        using (var response = await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, ct).ConfigureAwait(false))
        {
            ct.ThrowIfCancellationRequested();
 
            using (var content = response.Content)
            {
                var stream = await content.ReadAsStreamAsync().ConfigureAwait(false);
                var json = await ParseStream(stream, response);

                return json.RootElement;
            }
        }
    }

    private static async Task<JsonDocument> ParseStream(Stream stream, HttpResponseMessage response)
    {
        if (stream == null || stream.CanRead == false)
        {
            return default;
        }

        HttpStatusCode status = response.StatusCode;
        StatusCode.status = status.ToString();
        StatusCode.value = (int)status;

        using (var json = await JsonDocument.ParseAsync(stream).ConfigureAwait(false))
        {
            if (!response.IsSuccessStatusCode)
            {
                throw new ApiException()
                {
                    Content = json.RootElement.ToString(),
                    StatusCode = status.ToString(),
                    value = (int)status,
                };
            }
            return json;
        }
    }

更新：（这是我试过的）

     public static async Task<JsonDocument> ParseJsonData(string api, CancellationToken ct)
        {
            clientHandler = new HttpClientHandler()
            {
                UseProxy = Proxy.IsUseProxy ? true : false,
                Proxy = Proxy.IsUseProxy ? new WebProxy($"{Proxy.ProxyHost}:{Proxy.ProxyPort}") : null,
                ServerCertificateCustomValidationCallback = (sender, certificate, chain, errors) => { return true; }
                // SslProtocols = SslProtocols.Tls12 | SslProtocols.Tls11 | SslProtocols.Tls
            };
            var uri = new Uri(api, UriKind.Absolute);
            utils.SetConnection(uri);
            client = new HttpClient(clientHandler);

            using (var request = new HttpRequestMessage(HttpMethod.Get, uri))
            {
                AddRequestHeaders(request, uri);
                return await ResponseMessage(request, ct);
            }
        }
        private static async Task<JsonDocument> ResponseMessage(HttpRequestMessage request, CancellationToken ct)
        {
            using (var response = await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, ct).ConfigureAwait(false))
            {
                ct.ThrowIfCancellationRequested();
                HttpStatusCode status = response.StatusCode;
                
                using (var content = response.Content)
                {
                    var stream = await content.ReadAsStreamAsync().ConfigureAwait(false);

                    if (stream == null || stream.CanRead == false) { return default; }

                    var options = new JsonDocumentOptions { AllowTrailingCommas = true };
                    var json = await JsonDocument.ParseAsync(stream, options).ConfigureAwait(false);
                    
                    if (!response.IsSuccessStatusCode)
                    {
                        throw new ApiException()
                        {
                            Content = json.RootElement.ToString(),
                            StatusCode = status.ToString(),
                            value = (int)status,
                        };
                    }
                    return json;
                }
            }
        }

   public static async Task<test> GetData(string id, CancellationToken ct)
    {
        string API = $"https://www.test.com/api/videos/{id}";

        using (var root = await MyClientHelper.ParseJsonData(API, ct))
        {
            var json = root.RootElement;

            //here i can access the root and dispose after

            return new test()
            {
                /////
            }
        }
    }

Answer 1

这就是 using 的工作方式。当您离开 using 子句时，该对象将被释放。那是故意的。

所以请考虑您的代码：

using (var json = await JsonDocument.ParseAsync(stream).ConfigureAwait(false))
        {
            if (!response.IsSuccessStatusCode)
            {
                throw new ApiException()
                {
                    Content = json.RootElement.ToString(),
                    StatusCode = status.ToString(),
                    value = (int)status,
                };
            }
            return json; <------ the moment you return it you also dispose it
        }

因此，当您尝试从外部访问它时，您会收到错误消息：

    var json = await ParseStream(stream, response);
    // here your object is already disposed
    return json.RootElement;

解决方案：在存在解析函数之前，return 你的json。 JsonDocument 对象不应在 using 子句之外使用。

作为解决方法，您不应忽略处理对象：https://docs.microsoft.com/en-us/dotnet/api/system.text.json.jsondocument?view=netcore-3.1

Failure to properly dispose this object will result in the memory not being returned to the pool, which will increase GC impact across various parts of the framework.

Answer 2

幸运的是，有 Clone() 方法。所以而不是：

using JsonDocument doc = JsonDocument.Parse(jsonString);
return doc; // or return doc.RootElement;`

你可以这样做：

using JsonDocument doc = JsonDocument.Parse(jsonString);
var root = doc.RootElement.Clone();
return root;

"获取可以在原始 JsonDocument 的生命周期之后安全存储的 JsonElement。" https://docs.microsoft.com/en-us/dotnet/api/system.text.json.jsonelement.clone?view=net-5.0

System.Text.Json 无法访问处置 jsonDocument

System.Text.Json Cannot access a dispose jsonDocument

c#

system.text.json