在ASP.NET Web Api中使用"ExceptionHandler"需要一个完整的示例来处理未处理的异常？

Question

我查看了这个链接 http://www.asp.net/web-api/overview/web-api-routing-and-actions/web-api-global-error-handling.在这个链接中他们提到了这样的

class OopsExceptionHandler : ExceptionHandler
{
    public override void HandleCore(ExceptionHandlerContext context)
    {
        context.Result = new TextPlainErrorResult
        {
            Request = context.ExceptionContext.Request,
            Content = "Oops! Sorry! Something went wrong." +
                      "Please contact support@contoso.com so we can try to fix it."
        };
    }

    private class TextPlainErrorResult : IHttpActionResult
    {
        public HttpRequestMessage Request { get; set; }

        public string Content { get; set; }

        public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
        {
            HttpResponseMessage response = 
                             new HttpResponseMessage(HttpStatusCode.InternalServerError);
            response.Content = new StringContent(Content);
            response.RequestMessage = Request;
            return Task.FromResult(response);
        }
    }
}

我不知道如何在我的Web API操作中调用此类.所以任何人都可以使用这个给我完整的样本ExceptionHandler.

Answer 1

您不需要自己实现IExceptionHandler低级机制.

相反,您可以简单地从ExceptionHandler继承并覆盖Handle方法.

public class MyExceptionHandler: ExceptionHandler
{
  public override void Handle(ExceptionHandlerContext context)
  {
    //TODO: Do what you need to do
    base.Handle(context);
  }
}

ExceptionHandler实现IExceptionHandler并管理基本的核心机制(如异步和应该处理的异常).

像这样使用你的异常处理程序:

config.Services.Replace(typeof(IExceptionHandler), new MyExceptionHandler());

资源

本页介绍了如何实现IExceptionHandler,但是有一些拼写错误,而且代码没有反映最新版本的WebApi.

没有关于System.Web.Http.ExceptionHandling命名空间的文档(关于NuDoq的一点点).

所以.. 使用.NET程序集反编译器查看GitHub上的源代码,我看到了ExceptionHandler实现IExceptionHandler并具有一些虚拟方法的类.

ExceptionHandler看起来像这样:

namespace System.Web.Http.ExceptionHandling
{
    /// <summary>Represents an unhandled exception handler.</summary>
    public abstract class ExceptionHandler: IExceptionHandler
    {
        /// <returns>Returns <see cref="T:System.Threading.Tasks.Task" />.</returns>
        Task IExceptionHandler.HandleAsync(ExceptionHandlerContext context, CancellationToken cancellationToken)
        {
            if (context == null)
            {
                throw new ArgumentNullException("context");
            }
            ExceptionContext arg_14_0 = context.ExceptionContext;
            if (!this.ShouldHandle(context))
            {
                return TaskHelpers.Completed();
            }
            return this.HandleAsync(context, cancellationToken);
        }

        /// <summary>When overridden in a derived class, handles the exception asynchronously.</summary>
        /// <returns>A task representing the asynchronous exception handling operation.</returns>
        /// <param name="context">The exception handler context.</param>
        /// <param name="cancellationToken">The token to monitor for cancellation requests.</param>
        public virtual Task HandleAsync(ExceptionHandlerContext context, CancellationToken cancellationToken)
        {
            this.Handle(context);
            return TaskHelpers.Completed();
        }

        /// <summary>When overridden in a derived class, handles the exception synchronously.</summary>
        /// <param name="context">The exception handler context.</param>
        public virtual void Handle(ExceptionHandlerContext context)
        {
        }

        /// <summary>Determines whether the exception should be handled.</summary>
        /// <returns>true if the exception should be handled; otherwise, false.</returns>
        /// <param name="context">The exception handler context.</param>
        public virtual bool ShouldHandle(ExceptionHandlerContext context)
        {
            if (context == null)
            {
                throw new ArgumentNullException("context");
            }
            ExceptionContext exceptionContext = context.ExceptionContext;
            ExceptionContextCatchBlock catchBlock = exceptionContext.CatchBlock;
            return catchBlock.IsTopLevel;
        }
    }
}

您可以清楚地看到ShouldHandle使用ExceptionContextCatchBlock.IsTopLevel和HandleAsync调用实现Handle:)

我希望这会有所帮助,直到完整的文档显示出来.

Answer 2

在您的WebApi配置中,您需要添加以下行:

config.Services.Replace(typeof (IExceptionHandler), new OopsExceptionHandler());

还要确保已创建实现IExceptionHandler的基本ExceptionHandler类:

public class ExceptionHandler : IExceptionHandler
{
    public virtual Task HandleAsync(ExceptionHandlerContext context, 
                                    CancellationToken cancellationToken)
    {
        if (!ShouldHandle(context))
        {
            return Task.FromResult(0);
        }

        return HandleAsyncCore(context, cancellationToken);
    }

    public virtual Task HandleAsyncCore(ExceptionHandlerContext context, 
                                       CancellationToken cancellationToken)
    {
        HandleCore(context);
        return Task.FromResult(0);
    }

    public virtual void HandleCore(ExceptionHandlerContext context)
    {
    }

    public virtual bool ShouldHandle(ExceptionHandlerContext context)
    {
        return context.CatchBlock.IsTopLevel;
    }
} 

请注意,这只会处理其他地方未处理的异常(例如,通过异常过滤器).