I am trying to understand custom exceptionhandlers but am not getting the hang of it. I tried implementing a custom exception handler like explained in the following pages:
https://www.exceptionnotfound.net/the-asp-net-web-api-exception-handling-pipeline-a-guided-tour/ https://docs.microsoft.com/en-us/aspnet/web-api/overview/error-handling/web-api-global-error-handling
Now my code is:
public class CustomRestErrorHandlerException : ExceptionHandler
{
public void CustomError(String error)
{
var message = new HttpResponseMessage(HttpStatusCode.NoContent)
{
Content = new StringContent("An unknown error occurred saying" + error)
};
throw new HttpResponseException(message);
}
public override void Handle(ExceptionHandlerContext context)
{
if (context.Exception is ArgumentNullException)
{
var result = new HttpResponseMessage(HttpStatusCode.BadRequest)
{
Content = new StringContent(context.Exception.Message),
ReasonPhrase = "ArgumentNullException"
};
context.Result = new ErrorMessageResult(context.Request, result);
}
else if (context.Exception is ArgumentException)
{
var result = new HttpResponseMessage(HttpStatusCode.NoContent)
{
Content = new StringContent(context.Exception.Message),
ReasonPhrase = "Argument is not found"
};
context.Result = new ErrorMessageResult(context.Request, result);
}
else if (context.Exception is ArgumentOutOfRangeException)
{
var result = new HttpResponseMessage(HttpStatusCode.NotImplemented)
{
Content = new StringContent(context.Exception.Message),
ReasonPhrase = "Argument is out of range"
};
context.Result = new ErrorMessageResult(context.Request, result);
}
else
{
CustomError(context.Exception.Message);
}
}
public class ErrorMessageResult : IHttpActionResult
{
private HttpRequestMessage _request;
private HttpResponseMessage _httpResponseMessage;
public ErrorMessageResult(HttpRequestMessage request, HttpResponseMessage httpResponseMessage)
{
_request = request;
_httpResponseMessage = httpResponseMessage;
}
public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
{
return Task.FromResult(_httpResponseMessage);
}
}
}
Then I try to call the exceptionhandler which I obviously do wrong : (this I probably do not understand <<
[Route("api/***/***")]
[HttpGet]
public IHttpActionResult Clear****()
{
try
{
// try clearing
}
catch(Exception e)
{
throw new CustomRestErrorHandlerException(); << error occurs here
}
return this.Ok();
}
As you can see the error occurs because the exception is not an exceptionhandler but I have no idea how to then throw an exception through an custom exception handler since it's explained nowhere.
Can anyone explain this to me with a small example perhaps?
Quote from: https://www.exceptionnotfound.net/the-asp-net-web-api-exception-handling-pipeline-a-guided-tour/ :
"The handler, like the logger, must be registered in the Web API configuration. Note that we can only have one Exception Handler per application."
config.Services.Replace(typeof(IExceptionHandler), new CustomRestErrorHandlerException ());
So add the line above to the WebApiConfig.cs file and then simply throw an exception from the controller:
[Route("api/***/***")]
[HttpGet]
public IHttpActionResult Clear****()
{
// do not use try catch here
//try
//{
// try clearing
//}
//catch(Exception e)
//{
//throw new CustomRestErrorHandlerException(); << error occurs here
//}
throw new Exception();
}
ExceptionHandler 's have to be registered in the Web API configuration. This can be done in the WebApiConfig.cs file as shown below, where config is of type System.Web.Http.HttpConfiguration
.
config.Services.Replace(typeof(IExceptionHandler), new GlobalExceptionHandler());
Once they are registered they are automatically called during unhandled exceptions. To test it out you might want to throw an exception in the action method such as:
[Route("api/***/***")]
[HttpGet]
public IHttpActionResult Clear****()
{
try
{
// try clearing
}
catch(Exception e)
{
throw new ArgumentNullException(); << error occurs here
}
return this.Ok();
}
You can now put a breakpoint in your exception handler and see how the unhandled exception is caught by the global ExceptionHandler.
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