Question

我正在.NETCore（2.2.0）中创建一个需要同时支持XML和JSON的API。对于绝大多数端点，默认情况下它必须以XML响应，但是如果客户端请求，则应遵循“ Accept”标头以返回JSON。工作正常。

一个控制器是一种特殊情况，因为它仅需要支持JSON，并且具有作为字典的响应。对此控制器的请求会产生正确的JSON响应，但是在我的日志中，我看到一个System.NotSupportedException，该异常源自“ Microsoft.AspNetCore.Mvc.Formatters.XmlSerializerOutputFormatter.CreateSerializer”

如果删除操纵OutputFormatters列表顺序的代码，则看不到异常。

在startup.cs中，我的ConfigureServices方法包含以下内容：

services.AddMvc()
    .AddXmlSerializerFormatters();
            services.Configure<MvcOptions>(options =>
            {
                var outputFormatters = options.OutputFormatters;
                var jsonOutputFormatter = outputFormatters.First(f => f is JsonOutputFormatter);
                // Remove JSON output formatter and reappend at end to default to XML
                outputFormatters.Remove(jsonOutputFormatter);
                outputFormatters.Add(jsonOutputFormatter);

                // Allow the client to request other content types (JSON)
                options.RespectBrowserAcceptHeader = true;
            });

可以使用以下控制器再现该错误。

[Route("api/[controller]")]
[Produces("application/json")]
[ApiController]
public class ExampleController : ControllerBase
{
    [HttpGet]
    public IActionResult GetDict()
    {
        return Ok(new Dictionary<int, string>());
    }
}

调用GET / api / Example时会产生以下警告/错误，并且在'Accept'标头为'application / json'或未提供时都会发生。

Microsoft.AspNetCore.Mvc.Formatters.XmlSerializerOutputFormatter:Warning: An error occurred while trying to create an XmlSerializer for the type 'System.Collections.Generic.Dictionary`2[[System.Int32, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[System.String, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]]'.

System.NotSupportedException: The type System.Collections.Generic.Dictionary`2[[System.Int32, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[System.String, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]] is not supported because it implements IDictionary.
   at System.Xml.Serialization.TypeScope.GetDefaultIndexer(Type type, String memberInfo)
   at System.Xml.Serialization.TypeScope.ImportTypeDesc(Type type, MemberInfo memberInfo, Boolean directReference)
   at System.Xml.Serialization.TypeScope.GetTypeDesc(Type type, MemberInfo source, Boolean directReference, Boolean throwOnError)
   at System.Xml.Serialization.ModelScope.GetTypeModel(Type type, Boolean directReference)
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(Type type, XmlRootAttribute root, String defaultNamespace)
   at System.Xml.Serialization.XmlSerializer..ctor(Type type, String defaultNamespace)
   at System.Xml.Serialization.XmlSerializer..ctor(Type type)
   at Microsoft.AspNetCore.Mvc.Formatters.XmlSerializerOutputFormatter.CreateSerializer(Type type)

有没有一种方法可以防止此警告，但默认情况下仍保持所有其他以XML响应的控制器的预期行为？

为什么在序列化为JSON时创建XML序列化器？

0 个答案: